PLANT DEVELOPMENT INTHE
ABSENCE OF BORON
BY
MARIE P. LÖHNI5
Mededeelingen van de Landbouwboogeocbool
Deel 41 .—• Verhandeling 3
H . V E E N M A N & Z O N E N — W A G E N I N G E N — 1937
V^WW^
PLANT DEVELOPMENT
IN THE ABSENCE OFBORON
Dy A t a r i e P . L ö n n i s
1. SIGNS OF BOEON DEFICIENCY
a. Introduction.
The fact t h a t t h e element boron is essential t o a healthy developm e n t of m a n y plant species has been established b y several authors.
I n plants deprived of boron t h e initial disturbance occurs in t h e
growingpointsof shoots a n droots, whilesubsequently full-grown leaves
become discoloured a n d withered in order from t h e apex downwards.
This sensitiveness t o t h e deficiency of boron has been definitely
established b y means of nutrient solutions for:
Vicia faba ( W A B I N G T O N , 1923. s ' J A C O B , 1927).
Phaaeolus multiflorus (WABINGTON, 1923).
Trifolium i n c a r n a t u m
id.
Linum usitatissimum (SOMMEE a n d L I P M A N , 1926).
Helianthus annuus
id.
Ricinus communis
id.
Sinapis alba
id.
Glycine hispida ( B E E N C H L E Y a n d W A B I N G T O N , 1927).
Cucumis melo
Trifolium minus
Trifolium repens
id.
id.
id.
Trifolium p r a t e n s e ( B E E N C H L E Y a n d W A B I N G T O N , 1927. G I L B E R T a n d
PBMBEE,
1931).
P o l y g o n u m fagopyrum ( B E E N C H L E Y a n d W A B I N G T O N , 1927. SOM-
MEE, 1927).
Nicotiana t a b a c u m (SWANBACK, 1927. MCMXJETBEY, 1929. M E S , 1930).
B e t a vulgaris ( S O M M E E , 1927. BEANDENBTJEG, 1931).
Solanum tuberosum ( J O H N S T O N , 1928. V A N S C H E E V E N , 1934).
Solanum lycopersicum ( J O H N S T O N a n d D O E S , 1929. J O H N S T O N a n d
F I S H E E , 1930).
Citrus ( H A A S a n d K L O T Z , 1931). •
Lactuca sativa (MOHARGTTE a n d C A L F E E , 1932).
Gossypium ( E A T O N , 1932).
Saccharum officinarum (VAND E N H O N E E T , 1932. M A R T I N , 1934).
Fragaria vesca ( H O A G L A N D a n d S N I J D E E , 1933).
Zea mays ( O V E R B E E K , 1934. T A B E E E L T I N G E , 1936).
Vitis finifera ( E A T O N , 1935).
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Brassica napus ( O ' B R I E N a n d D E N N I S , 1935).
Lupinus luteus (VAN G E N N E P , 1936).
Sorghum vulgare (GROSSENBAOKER a n d L I V I N G S T O N , 1936).
Coffea ( S ' J A C O B , 1936).
Ribes r u b r u m ( L Ö H N I S , 1937).
Apium graveolens ( P U R V I S a n d R U P R E C H T , 1937).
Conclusive evidence is lacking for:
Medicago sativa ( B R E N C H L E Y a n d W A R I N G T O N , 1927).
Phaseolus vulgaris ( W A R I N G T O N , 1923. S ' J A C O B , 1927).
F o r some plants conflicting results have been reported b y various
authors. These are:
Pisumsativum ( W A R I N G T O N , 1923.B R E N C H L E Y a n d W A R I N G T O N , 1927.
S ' J A C O B , 1927. W A R I N G T O N , 1933. L Ö H N I S , 1936).
H o r d e u m vulgare ( W A R I N G T O N , 1923. SOMMER a n d L I P M A N , 1926
BRENCHLEY
a n d W A R I N G T O N , 1927. W A R I N G T O N , 1933).
F o r a fewspecies boron isdeemed unessential. These are:
Vicia villosa ( W A R I N G T O N , 1923).
Iberis umbellata ( B R E N C H L E Y a n d W A R I N G T O N , 1927).
Secale cereale ( W A R I N G T O N , 1923. SCHARRER a n d S C H R O P P , 1933).
Triticum vulgare ( M O R R I S , 1931. S C H A R R E R a n d S C H R O P P , 1934).
The present a u t h o r h a sgrown m a n y plant species, with t h eview t o
1° comparing t h e stage of growth in which t h e initial symptoms
of boron deficiency m a ybe noted.
2° investigating whether actually a n y higher plants exist which
m a y reach full development int h eabsence of boron.
All experiments have been carried o u t in culture solution. T h e
nutrient solution ofv a n derCrone, modified according t o B R Y A N (1921)
was used. Traces ofelements according t ot h eformula of SOMMER a n d
1
S O R O K I N (1928) were a d d e d ) . So in t h e complete nutrient solution
boron wassupplied as 0.5 mg boric acid per Utre. Chemically pure
salts were used without a n y further recrystallisation. P l a n t s were
grown in commercial glass j a mjars of 300cc. After use t h e jars were
cleaned inboiling very dilute HCl a n drinsed with water. After repeated
use t h ejars became sowell seasoned t h a t results int h eboron deficient
cultures were very satisfactory. Theplantlets were p u tu p in holes of
t h e paraffined metal lids. Thejars were wrapped u pfirst i n black a n d
t h e n inwhite paper. T h ecultures were kept in a small unheated green
house. Harmful insolation could bekept offb ymuslin curtains. Germination was effected in moist sand a n d as soon as t h e rootlets h a d
M KN0 3 1g; KCl 0,75g; CaS0 4 2H,0 0,2g;MgS04 7H 2 O0,2g; Ca,(POt)2
0,2 g; FeP0 4 0,2g; H3BO? 0,5mg;MnS0 4 1,5mg;Alj(S04)8 0,6 mg;CuS0 4
0,125 mg;K J 0,25mg, 1litre water.
attained the length of a few cm plantlets were put up in the culture
vessels. The water lost in transpiration was replaced daily. According
to the rate of growth the nutrient solution was renewed; in periods
of rapid growth this was doneeverytwoweeks.These conditions allowed of good growth. For nearly all the species put tothetest van der
Crone solution was a very good culture medium; only tomatoes did
not thrive very well and grew better in Zinzadze solution pH5 (1927).
In every experimental series a comparison was made between cultures where the nutrient salts were supplied in distilled water a with,
and bwithout any additional boron and cin tapwater without additionalboron.For the sake of brevity these solutions will be designated as
a distilled water (—B), bdistilled water ( + B ) and ctapwater (—B).
Experiments havebeen put upin duplicate, and all[of them have been
put up repeatedly during succeeding summers.
Thecultureswere kept up till the moment when the first symptoms
of deficiency could be noted in the (—B) series. In the tapwater (—B)
this occurred later than in the distilled water (—B), due to the traces
of boron present in the tapwater. In the tapwater 0.001 mg boron
could be detected in 1\ litre (Method page 19).Therefore the distilled
water (—B) had to be set up later than the tapwater (—B) in order
that a photograph could be made of newly affected plants in both
series. As a matter of fact the stage in which the distilled water ( + B )
series are taken is quite a random one. They might have continued
their development, while by lack of boron the development in the
(—B).sets was brought to a close.
b. Plant speciesfor whichtheessentialnature ofboronhadbeendefinitely established byformer authors.
Severalofthese species have been studied by the present author and
the results invariably corroborated the results of former workers.
Although invariably a similar salt mixture had been used for the
nutrient solutions, the initial deficiency symptoms occurred at different stages of development in the various plant species studied. Fig.
1—7 show the results attained with: sugar beet, Trifolium repens,
Trifolium campestris, Trifolium incarnatum, tomato (Var. William
Copelemd),Nicotiana tobacum (Var. atropurpurea) and Vicia faba. In
the diBtilled water (—B) cultures this must be due to a difference in
the boron content of the seed as well as a difference in need of boron
for development. The differences in development between distilled
water (—B) and tapwater (—B) cultures of a same plant species can
be only accounted for by different boron requirements in the various
specieB studied.
I t appeared to be possible aswellto induce signs of boron deficiency
by growing plants not from seed, but from cuttings.
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The results with cuttings of Ribes rubrum have been reported by
the present author (1937) as follows: In a distilled water (—B) culture
the youngest leaflet was brown and shrivelled and had a black petiole.
Theneighbouring leaveswereedgedwith awide,dry,light brown band
and only a narrow zone in the centre of the leaf was green. One of the
basal leaves of the shoot had rusty brown marginal spots, the other
basal leaves were healthy.
In 1934similarresults wereattained with grapes (Var. Frankentaler).
Cuttings had rooted in a heated green house in winter and were grown
in nutrient solution from February 1stto May 17th.Bythattimeinthe
distilled water (—B) set the lateral roots were very short and stunted
with dark-coloured root tips. The shoot was very short with leaves
turned downward towards the stem. In the youngest leaf the chlorophyll was faded out and only the main nerves were green. The neighbouring leaves had taken on a wine-red or orange colour, the nerves
weregreen. The oldest leaf was ofa very dark green. In tapwater (—B)
the development of the root-system was much better, the numerous
adventive roots however bore astunted appearance. Someofthe leaves
had a narrow wine-red band along the margin. The plants in the
distilled water ( + B ) set were quite healthy. Fig. 8 shows the results.
c. Plant speciesfor whichconclusiveevidencewas lacking.
Medicagosativa. BRENCHLEY and WARINGTON (1927) state: „In all
probability lucerne belongs to this group, as the plants without boron
were poor and showed a distinct tendency to develop a characteristically stunted root system, but conclusive evidence at the flowering
stage was lacking and all plants were severely injured with aphis
infestation."
Accidently it was the lucerne which brought me to the study of
boron deficiency ;with other aimsin view solution culturesin tapwater
with lucerne were carried out in 1932 and again and again injury
occurredintheplantsspreadingfrom the apex downward. Initially the
damage was ascribed to unfavourable conditions in the green house.
Aftertheadditionhowever, oftraces ofelements as applied by SOMMER
and SOROKIN quite another light was thrown on the question.
In fact, after the supply of the elements to the solution, the lateral
buds ofplants withthe affected apices,inwhich development had been
arrested, developed into healthy side shoots, and the root system commenced growth again. Very soon healthy young shoots had taken the
place of the affected parts. When traces of the other elements were
supplied and only boron was left out, the same symptoms occurred
and addition ofboron resulted into new growth. Solucerne apparently
was very sensitive to boron deficiency (fig. 9).
Description of the symptoms. In distilled water (—B) cultures the
symptoms of deficiency occur at a very early stage of development.
The main root and laterals remain very short and stumpy and only
very few leaves are formed which from the outset are deformed and
mottled. In tapwater (—B) cultures the main root and laterals remain
short and stunted. In the shoot theinitial symptoms occurinthe apex;
the youngest leaves develop narrow lamina dotted with yellow spots.
Gradually the injury spreads downward from the apex;initially sound
leaves grow mottled and turn yellow and dry. The side shoots start
growing and bear small mottled leaves;very soon however these side
shoots stagnate in growth. When boron deficiency occurs at a stage
when the lucerne is already fairly well developed, after the growth
of the apex is brought to a stand-still many af the lower leaves may
remain healthy. The lowest leaves however grow appreciably thicker
than normally and the edges growwhite. Apparently secundary symptoms are met with here;as the meristem does not develop any further
no more food stuffs are transported to the apex and the oldest leaves
will be stuffed with carbohydrates.
Phaseolus vulgaris. WAKINGTON (1923) reports the following results
for Dwarf bean (Var. Sutton's Canadian Wonder):For some time all
the plants wererather poor, probably owingto seasonal conditions and
it wasimpossible to note any appreciable difference between the sets,
owingtothegreatlackofuniformity. However after about three weeks'
growth the boron-treated plants ran ahead of the controls, both root
and shoot being better developed though no striking contrast between
the type of the root was apparent. The control plants made very little
growth indeed and eventually all died, yetatfirst theywereeven ofa
better green colour than the treated plants;the latter were decidedly
yellowish, but grew to fair-sized plants, flowered and in some cases
fruited, s'JACOB (1927) could not evoke any symptoms of deficiency
in Phaseolus vulgaris, working with Dwarf bean with a brown skin
(Bruine boon).
I put a white-skinned runner bean (Prinsesseboon) to the test. I t
appeared to be highly sensitive: even before the cotyledones were
shrivelled up the development came to a close! In the distilled water
(—B) set only the pair of primary leaves developed (fig. 10)
Similar results could be recorded for Dwarf bean with brown skin
(Bruine boon). An experiment was run from May 27th to June 15th.
In the distilled water (—B) set plants bore only the pair of primary
leaves; in the tapwater (—B) set one further leaf developed (fig. 11).
When the same experiment however was run from September to the
middle of December the deficiency symptoms in the tapwater (—B)
set occurred at a much later stage;these plants produced four normal
leaveB before the development came to a standstill. In the distilled
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water ( + B ) set however plants had flowered and even fruited in t h e
same period (fig. 12).
The phenomenon t h a t t h e season m a y influence t h e occurrence of
boron-deficiency symptoms h a d been observed by m a n y authors.
W A R I N G T O N (1923), S ' J A C O B (1927), M E S (1930). I n 1933 W A R I N G T O N
has worked out this subject in a more detailed research.
d. Plant species which gave conflicting results as reported by various
authors.
Pisum sativum. W A R I N G T O N (1923) reports t h e pea (Var. Harbinger
a n d Pioneer) to be more or less independent of t h e presence of boron
though some slight beneficial effect is evident from t h e solution of
small quantities of boric acid t o t h e nutrient solution.
B B E N C H L B Y and W A R I N G T O N (1927) grow three varieties of garden
pea to full development in a solution without any additional supply
of boron.
S ' J A C O B (1927) reports a same result for t h e garden pea Var. Wonder
van Amerika.
W A R I N G T O N (1933) is able to induce deficiency symptoms in Sutton's
Harbinger.
LÖKNis (1936) reports t h a t boron is essential for eight varieties of
garden peas.
I n 19331grew the variety Kroonerwt, which gave definite symptoms
of boron deficiency in distilled water (—B) sets as well as in t a p w a t e r
(—B) fig. 13. As it might be conceived t h a t this variety was exceptionably sensitive,in 1934 t h e varieties Kroonerwt, Wonder van Amerika as
used b y S ' J A C O B , Venlosche Witte a n d Delicatesse were mutually compared. I n each jar two plants were grown a n d t h e experiment was
carried out in duplicate. The a m o u n t of water t h a t h a d to be replaced
was recorded. The results calculated per plant are t h e following:
TABLE 1.
BEHAVIOUR OF DIFFERENT VARIETIES OF GARDEN PEAS
Tapwater (-B)
Variety
Venlosche Witte
...
Wonder v. Amerika
Distilled w. (-B)
Dry
weight
Transp.
Dry
weight
0,38 g
0,37 g
0,36 g
0,25 g
104 cc
82 cc
67 cc
72 cc
0,22 g
0,17 g
0,18 g
0.20 g
Dry w.t a p w a t e r D r y w. distilled
Transp.
water
70 ce
57 ce
68 ce
51 ce
0.16 g
0,20 g
0,18 g
0,05 g
I n the t a p w a t e r (—B) set Wonder van Amerika is t h e lowest in d r y
weight a n d only 0.05 g over t h e d r y weight in distilled water (—B).
As far as these figures m a y indicate t h e degree of sensitiveness, Wonder
van Amerika is highly sensitive t o boron deficiency compared with
Krodnerwt.
The difference in r a t e of transpiration in t h et a p w a t e r set between
Wonder van Amerika a n d Kroonerwt is small; so t h e production of a
larger a m o u n t of organic m a t t e r in t h e absence of boron cannot be
explained byahigher intake ofwater, which int a p w a t e r cultures might
involve a higher intake of boron.
Apparently adifference indegree ofsensitiveness toboron deficiency
cannot explain t h eexisting conflicting results.
s'J A C O B h a d t a k e n t h eprecaution ofcoating his culture vessels with
paraffine wax. T h estock solutions however were stored in jena glass
a n d i t is conceivable t h a t traces of boron have been set free b y this
glass. W A R I N G T O N however h a da solution stored in a n uncoated flask
for six weeks analysed spectroscopically a n dno trace of boron could
be detected. Sheherself deems t h einconsistency in herown results in
t h e repeated experiments quite inexplicable.
Hordeum vulgare. W A R I N G T O N reports in 1923t h a t barley makes
approximately o p t i m u m growth int h eabsence ofa n y supply of boron.
I n 1927 B R B N C H L B Y and W A R I K G T O N report barley again as insensitive
to deficiency although t h e y point t o t h e incongruency with results
obtained b y SOMMER a n d L I P M A N in 1926. I n 1933 however W A R I N G -
TON oould report a n absence of t h e ears a n da n a b u n d a n t tillering in
barley grown without a n y supply of boron. Therefore boron appears
here t o be essential for full development. T h e difference in results
obtained in various years cannot be accounted for b y a difference of
content of boron in t h e seed ; in fact plants grown from a few grains,
which h a ddeveloped in a solution without a n ysupply of boron, when
grown without boron did n o t show deficiency symptoms a n y earlier
t h a n plants grown from normally cultivated seed.
I n 1933 I setu pt h e usual experimental groups of barley. The cultures were kept until t h eflowering stage int h e boron-supplied set was
reached. At t h a t m o m e n t t h e distilled water (—B) set showed plants
t h e roots a n dshoots ofwhich h a ddeveloped asprofusely asinthe other
sets. E a r s however could not benoted. They h a d produced m a n y young
tillers (15 in 3plants). I n t h edistilled water ( + B )set 3plants bore in
all 6ears a n d4tillers. I n t h et a p w a t e r (—B) sett h edevelopment was
quite like t h elatter set.
These results agree fully with t h elatter findings of W A R I N G T O N .
Ast h e plants h a d n o t been grown t o full m a t u r i t y , barley was t obe
p u t t o t h e test anew in 1936in order t o find o u t whether t h e grain
would reach m a t u r i t y in t h e t a p w a t e r (—B) set.I n t h e beginning of
May t h e experiment was started a n donJ u n e 23rd the six plants in this
set bore ears. The anthers were studied microscopically :t h e y contained
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sound pollen grains stuffed with starch. Pistils appeared sound as well.
On July 6th however the six ears together had only produced 3 grains
of normal size.Allthe other grains had stopped development at a very
young stage and were not over 3mmhigh.Apparently normal fecundation had occurred and the initial symptoms of boron deficiency
occurred during the development of the young grain.
Inthedistilledwater (—B)seton June 23rd no haulms had developed. The six budding ears varied at that date in length from 0.5 to
4 cm. In the largest ear spikelets could be clearly detected and it bore
long awns;its anthers were atrophied and contained deaf pollen grains
while the pistils appeared normal. Thus a young ear was formed in all
of the plants, but no emergence offlowering parts took place.
e. Plant speciesfor which boronwas reported as unessential.
Vicia villosa (Winter vetch). WARINGTON reports in 1923 that no
difference could be noted between sets of winter vetch when supplied
with or deprived of boron;neither set however flowered.
In 1933 the usual experimental range was put up on April 14th.
The set in distilled water (—B) showed symptoms in a fairly early
stage of development. The lateral roots were short and stumpy. The
upper leaves in the apex of the main and lateral shoots were narrow
and curled up over the upper surface. The neighbouring leaves took
on a yellow shade.At the root neck short sideshoots developed. In the
tapwater (—B)set the injury occurred at a fairly late stage of development. The symptoms in the shoot differed from those usually noted
in as much as the youngest leaves were unaffected, while initially the
5th and 6thleaf downward from the apex took on a reddish hue mostly
in the veins.Later the younger leaves were affected as well.A healthy
root system had developed before stumpy laterals occurred. Fig. 14
shows that in tapwater (—B) the injury occurred at a decidedly later
phase than in other plant species. This low sensitiveness may account
for the absence of injury in the cultures of WARINGTON.
Vicia sativa was put to the test aswell.It didnot differ in behaviour
from the main other species tested and the deficiency symptoms
occurredinafairly youngstageintapwater aswell as in distilled water
(—B).
Iberis umbellata (Candy Tuft). BRENCHXEY and WARINGTON report
in 1927 that Iberis umbellata came to full development in a nutrient
solution devoid of any added boron.
Several experiments were carried out by the present author in
succeeding years, each of them in duplicate. In 1933 the first experiment was set up on April 14th. On May 23rd no difference between
those in distilled water (—B) and tapwater (—B) could be observed;
il
in both sets buds of an inflorescence could be discerned and the vegetative!development was the same; the leaves however in the distilled
water (—B) set were somewhat thicker andturned downward towards
the stem. On July 4th in the distilled water (—B) set the plants had
developed healthy root systems; the inflorescences however were still
inthesamebudding stage and the leaveswere adpresed with the underside to the stem. In an experiment set up on May 3rd the plants in the
distilled water (—B) set had reached the flowering stage on July 23rd
at a much lower level of vegetative development than in the former
experiment. The flowers however withered.
In 1934experiments were set up again on April 14th.In the distilled
water (—B) set no flowers were produced. In the tapwater (—B) set
someinflorescences bloomed quite normally, but bore no seed, while
one inflorescence produced some ripe seed able to germinate. In the
distilled water ( + B ) set ripe seed developed.
In 1935the experiment began on April 9th. Fig. 15dates from July
8th. The plants of the distilled water (—B) set had long slender roots
without any symptoms ofinjury ;noinflorescence however developed.
In the tapwater (—B) and distilled water (+1$) plants reached a similar degree of vegetative development and bore inflorescences in full
bloom. The plants were kept up till the beginning of September. Although all inflorescences had fruited quite evenly all fruit appeared
to be parthenocarp: no seed could be harvested either from distilled
water ( + B ) or from tapwater (—B).
So in 1936 an attempt was made once more to obtain seed in the
tapwater (—B)set. Cultures were set up on May 7th and werein flower
on July 13th in the distilled water (—B) as well as in the other sets.
Fruiting occurred only in the distilled water ( + B ) and tapwater (—B)
sets. From one plant of the latter set ripe, though small, seed were
obtained;the other plant had succombed earlier.
These data provide evidence that Iberis umbellata is much less
sensitive to boron deficiency than the other Dicotyledons studied up
to the present. In distilled water (—B) no injury can be observed in
the root system, although it remains smaller than in the presence of
boron. The traces of boron supplied as impurity by the tapwater
appear to suffice in sustaining the plants up till full development,
including the formation of seed.
Moreover it can be noted, that after early sowing (April 4th, 14th
and 9th) vegetative development is at a higher level at the moment
offlowering than when the seed is sown later (May 23rd and 9th). In
the latter case the inflorescences bloom even in the distilled water
(—J5) set. As it has not been proved experimentally that these discrepancies are due to a difference in the length of day, it can only be
considered as probable.
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B R E N C H L E Y and W A R I N G T O N do not report in which season t h e y
have carried out the experiment with Iberis umbellata. During t h e
period of long days Iberis might be a p t to appear insensitive to boron
deficiency, while even in another season if t h e plants h a d access t o
minute traces of boron t h e y might come to full development as is
shown in the cultures in t a p w a t e r (—B).
Secale cereale. W A R I N G T O N notes full development in rye when no
boron has been added. S C H A R R E R a n d S C H R O P P (1936) grew rye in
culture solution of v a n der Crone without additional boron u p to t h e
flowering stage. I t is n o t stated whether distilled water was used.
I p u t u p an experiment with winter rye in t h e a u t u m n of 1933.
E a c h culture vessel contained 3 plants. On April 27th ears could be
seen in all of t h e cultures. B y May 22th t h e upper p a r t of t h e ears in
t h e distilled water (—B) set were dry a n d withered; although t h e glumes in the lower p a r t were sound no blooming occurred. I n b o t h t h e
other sets all ears were flowering (fig. 16). On J u n e 26th in t h e distilled
water (—B) set all ears were deaf; t h e plants h a d developed some
young green tillers. I n the t a p w a t e r (—B) set all of t h e 6 ears were
evenly beset with ripe grain; no young tillers occurred. The distilled
water ( + B ) set was similar.
I n 1934-'35 seed was grown derived from plants cultivated in t a p water (—B), t h u s developed in the presence of only traces of boron.
I t was compared with t h a t of seed grown in distilled water ( + B ) o r
in the open, where during ripening there was a good supply of boron.
The three sets each in duplicate were p u t u p in distilled water (—B).
Similar phenomena of boron deficiency as observed in 1934 occurred
in all of t h e plants at t h e same moment.
Any influence of origin of seed on the stage of development where
deficiency symptoms occurred could n o t be noted. This agrees well
with the observations m a d e b y W A R I N G T O N for barley.
The content of boron has been estimated (for method see page 19)
in samples of either lot of seed which has been used for sowing; a same
amount was found, viz. 0.3 parts per million on the basis of d r y weight.
Triticum vulgare. Very scanty information was available for t h e behaviour of wheat in t h e absence of boron. M O R R I S (1931), who studied
the injury caused b y an overdose of boron records the occurrence of
a b u n d a n t tillering in a boron free-medium. She however does not conclude t h a t boron is essential. S C H A R R E R and S C H R O P P (1934) could n o t
induce any deficiency symptoms b y growth in a boron free culture
solution, b u t t h e y did not grow t h e plants u p t o the flowering stage.
I n t h e a u t u m n of 1933 I p u t u p winter wheat ^Var. Wilhelmina).
P l a n t s in the three sets developed very well vegetatively and on J u n e
13
6th all plants bore ears. On July 5th in the distilled water (—B) set
however grain was completely lacking, while in the tapwater (•—B) set
andIjhedistilledwater ( + B ) all ears were evenly beset with ripe grain
(fig- H).
In 1934—'35 the experiment was repeated with the aim of getting
a clearer notion about the cause of this absence of fruiting. When the
ears were studied at the time offlowering it could be noted, that in the
distilled water (—B) set quite healthy-looking pistils occurred; the
anthershowever,werequite atrophied and shrivelled up(fig. 18and19).
All of the flowers studied showedthisphenomenon, while in the tapwater (—B) as well as in the distilled water ( + B ) set all anthers had
developed normally and bore good pollen (fig. 20).
This absence of pollen might be the actual cause or one ofthe causes
which induced infertility. On a"very small scale it was tried whether
pollinationwith normalpollen might inducefruiting inplants deprived
of boron. 12 plants were pollinated and all together 12 grains were
formed. The growth ofthese grains however wasveryslight:theymerely reached a length of 3 mm.
Apparently pistilsgrowninamediumfree of boron may be functionally sound. For full development of the young grain however boron
appears te be essential.
In 1936it wastried whether full grown grain would beformed, when
plants which up till the moment of flowering had been supplied with
boron were at that moment removed to a boron-free medium. In
controlplants suppliedwithboron uptillthe endsound grains occurred
evenly all over the ear. In the cultures deprived of boron in the last
period however in 6ears studied full grown grain occurred quite densely in the lower third part of the ear, in the middle part the grain occurred more sparsely and the top part bore hardly any grain.
Here again for abundant fruiting boron appears to be essential.
I n 1934 grain ripened in the tapwater (—B) culture was compared
with»grain supplied with boron during its growth. The plants from the
seedlofdifferent origin were allgrown in culture solution prepared with
distilled water without boron. Deficiency symptoms in the different
sets occurred at the same stage of development, viz. atrophy of the
anthers. Asin rye the origin ofthe seed bore no influence on the occurrence of the deficiency symptoms. Here again an equal content of
boron was detected in the samples of each lot of seed, viz. 0.3 parts
per million on the basis of dry weight.
Avena sativa. No information was available on the development of
•oats in the absence of boron.
In 1933the cultures of oats had been put up rather late and plants
«ould not be grown to full maturity. On July 24th in all of the sets
3
3
14
the vegetative growth of roots and shoots was profuse and all plants
bore well-shot healthy ears (fig. 21).
In 1935 the experiment was repeated at an earlier date in order to
attainfull maturity in the grain. On June 18th all plants were healthy
andflowering.Theflowerswereinvestigated and onfirst view no difference could be noted between the ( + ) and (—) sets: allflowers appeared to contain well-developed anthers and pistils. When however the
anthers after a clearing in chloral hydrate were stained with iodine a
striking difference could be noted. While the pollen grains in the anthersfromtapwater(—B)anddistilledwater(+B) sets were invariably
stuffed with starch grains (fig 22, 1), the anthers of the distilled water
(—B) set either contained none but empty pollen grains (fig. 22, 2)
or a mixture of empty and sound ones (fig. 23),taken asafact that the
starchcontent actuallyindicatesahealthydevelopment (fig. 24and25).
Apparently theinitialsymptoms ofboron deficiency occurred during
the development ofthe pollen grain, at the timethe anther had already
reached its full size. The occurrence of starch grains is conceived as
the result of the presence of living protoplasm in the pollen grain;
there is no reason to suppose any direct influence of the presence of
boron on the carbohydrate metabolism.
On July 8th in the distilled water (—B) set none but very poorly
developed grain occurred;their length onlyreached 2mm. In the other•
cultures healthy milkripe grain of 1cmlength had developed.
When in 1936 the experiments were repeated the anthers in the
distilled water (—B)set contained chiefly a mixture ofsound and deaf
pollen grains. In 4 culture vessels devoid of boron the grain produced
had not developed over a length of 2 or 3mm, while in the other sets
sound pollen grains and grain of 1cmlength was produced. These results arein accordance with those obtained in 1935.
Allium cepa. As the Gramineaeappeartodiffer verymuchin behaviour from the main Dicotyledons studied, it was deemed worth while
to study aMonocotyledon ofanother family. The onion (Var. Bijnsburger)was chosen.
In 1935the seed was sown on June 5th. OnJuly 19thin the distilled
water (—B) set the plants bore short stumpy roots and withered leaf
tips. The dry weight per plant was 0.04 g, a very low value. On the
same date the tapwater (—B) plants did not show any characteristic
symptoms;they had however kept behind in development compared
withthe distilledwater ( + B ) set(fig. 26).OnAugust 23rdyoung onions
had formed in tapwater (—B) as well as in the distilled water (+B)
set. In the former set the bulbs were smaller; when cut open no macroscopic symptoms of injury could be detected.
I t appears that Allium cepa when deprived of boron shows the defi-
15
ciencjr symptoms at a very early stage of development. When however
tracei of boron are present it may proceed in development but at a
slowpace.
In |1936 seed bulbs were put to the test in cultures. Three bulbs
(Var. Mijnsburger) were put up in each set, approximatelythe same
weight in each. In every set however one had succombed before
full development was attained:the longstalks and heavyflower heads
had made them very top-heavy and accidents occurred. The experiment wasrun from April 14thto July 28th.The results arereported in
extenso as uniformity was not attained.
Initial weight
of bulb
g
97
94
94
86
97
84
Description of cultures
Distilled water (-B).
One head with healthy flowers. 9 fruits have set, b u t keep
back in' development and bear none b u t deaf seed. Two sound
young bulbs formed. Roots stunted (Fig. 27).
One head with flower buds mainly withered. No fruit or seed.
One sound young bulb. Boots stunted.
T a pwater (-B).
A head with flower buds mainly withered, only a few healthy
flowers. A head quite withered. One young bulb sound, one
rotting. Boots short a n d stunted (Fig. 27).
One head With flower buds withered. Three non-flowering
shoots. Four sound young bulbs. All roots stunted.
Distilled water ( + B ) .
One head bearing a profusion of healthy flowers. 35 ripe and
8 unripe fruit. Sound young bulb. Long roots (Fig. 27).
One head flowering profusely. Nearly every flower has fruited
and formed sound seed. A head flowering profusely, b u t stalk
h a d broken before fruiting occurred. Sound young bulbs. Many
long roots.
It appearsthat for theformation ofsoundroots,ofanormal amount
of flowers, and of any seed the boron presumably stored in the bulbs
does riot suffice nor do traces derived from the tapwater.
f. Discussion.
BRBNCHLEY and WARINGTON (1927) put the question whether any
higher plants which can reach full development in the absence of
boron exist and answer it in the following words: „It can be shown in
the present investigation that a sharp distinction can be drawn between plants for which boron is essential and those for which it is
beneficial only. The possibility however is not precluded that if a still
lower concentration could be achieved the latter class might merge
into tke former, the difference between the two classes proving to be
3
16
simply a matter of degree in their boron requirements." WARINGTON
herself contributed (1933) to the weakening of this distinction by
proving peas and barley to be sensitive to boron deficiency.
In the experiments carried out by me where I put all plant species,
deemed so far as insensitive to boron deficiency, to the test, I did not
meet with any species that could come to perfect development in the
absolute absence of boron.
As far as it has been tried experimentally, boron is an essential
element for all Angiosperms.
There is however an immense distance between Allium cepa, which
produces in the absence only 40 mg of dry weight, the lowest figure
found as far as the experimental plants have been weighed, and for
instance oats, where a healthy plant is produced, flowering and
bearing a dense mass of healthy roots, which only was kept from attainment of a still more profuse development by the small size of the
vessels used. Apparently among the Gramineae species occur which
areableto synthetisisetheirvegetative matterinthe absence of boron,
which in the main is impossible for Dicotyledons. The one exception
notedisIberisumbellata. In the distilledwater (—B)setoftheseplants
the root system although small never showed the characteristic
deficiency symptoms, on the contrary roots were as long and slender
as in the sets provided with boron. As for flowering it is again Iberis
umbellata, which may produce flowers in the total absence of boron
although generally the flower buds wither before maturity. Among
Cruciferae Brassica napus (Swedes) and Sinapis alba, however, are
known to be sensitive and in cultures of musterd grown by J. J. Lehr
in van der Crone solution prepared with distilled water (—B) I could
notice,that the development wasvery slightindeed. Sothe exceptional
behaviour ofIberis umbellata cannot be ascribed to its taxonomie
position.
When the tapwater (—B) cultures are mutually compared various
plant species attain different stages of development in the presence
of mere traces of boron. It is presumed the growth stagnation in the
distilled water (—B) cultures sets in when the boron stored in the seed
has been used up.The difference in development between plants grown
in tapwater (—B) and distilled water (—B) may indicate the boron
requirement ofthat species.
In a part of the experiments plants of the various sets were dried
and weighedat the stage ofoccurrence of initial symptoms. In Table2
the results are given.
The last column indicates the difference in weight between tapwater and distilled water sets and thus might indicate in which
degree boron was required. It is however hardly to be expected that in
comparing various plant species with widely varying habitats these
3
17
TABUS 2.
DBY WEIGHT AT THE INITIAL DEFICIENCY STAGE CALCULATED
PER PLANT
Yield in (-B) cultures
Species
Distilled water
Trifolium repens
Trifolium inoarnatum
Tobacco (var. a t r o p u r p u r e a ) .
Tobacco (var. Amersfoortea)
0,04 g
0,05 g
0,06 g
0,085 g
0,09 g
0,12 g
0,134 g
0,57 g
0,8 g
Tapwater - distilled w.
0,68 g
0,2
g
0,245 g
0,23 g
0,13 g
0,295 g
0,34 g
0,71 g
figures will have meaning. Moreover the size of the shoot developed
with the store of boron in the seed plays its part in the amount of
organic matter synthetisied together with the traces of boron from the
tapwater.
So a comparison of the figures may be no less an indicator of the
boron requirement of the plants studied.
Phaseolus vulgaris and sugar beet appear to stagnate in growth in
a.very early stage of development. So these plants aredeemedto have
a high boron requirement. For sugar beets this seems to agree with the
fact that in agricultural practice sugar beets are known to suffer from
a deficiency in boron: the heart-rot diseaseiscaused by boron deficiency as has been proven by BRANDENBURG (1931).
Viciavillosaontheother handreachesthe highest stageof vegetative
development among the Dicotyledons studied. Its symptoms of
deficiency however differ from those occurring in other Dicotyledons.
I n tine main the budding leaves bear the initial symptoms and are
badjy shaped. In Vicia villosa however the earliest symptoms occur in
initially welldeveloped healthy leaves.It looks asif boron ishere more
easily translocated than in other plants and is removed from the older
leaves to the meristematic parts.
l a the tapwater (—B) set Iberis umbellata has produced ripe seed
and is thus in behaviour very like the cereals studied.
The group of cereals agree so well in behaviour mutually that they
will be discussed together.
Zea mais isthe first plant for which it has been proven that boron is
beneficial (MAZE 1919). Any visible injury due to its absence however
was not detected. OVERBEEK (1934) describes symptoms of deficiency,
viz. white stripes in the leaves; the root system is normal although
somewhat smaller than in controls. TABER ELTINGE (1936) describes
3
18
the roots as brown and brittle. In experiments carried out by J. J.
Lehr (unpublished) I noted in distilled water (—B) cultures the white
stripes asdescribed by OVERBEEK and the existence ofperfectly sound
roots. GROSSENBAOKEB and LIVINGSTON (1936)describesimilar symptoms for Sorghum, viz. white stripes in the leaves and subsequently
almost white leaves. VAN DEN HONERT (1932) has studied sugar cane
and reports the occurrence ofwhite spots in the leaves, an extravagant
tillering, and stagnation of growth. MARTIN (1934) corroborates these
findings.
Maize, Sorghum and sugar cane are instances of the very large
Gramineae,whichbuildupexceedinglylargeamounts oforganic matter
at a very quick rate. Deficiency of an essential nutritional element
may be expected to occur in an earlier stage of development than in
slower growing plants. They are the only Gramineae where deficiency
symptoms occur inthe foliage. The only phenomenon inthe vegetative
part in other cereals is a tillering after the ear growth has stagnated.
The initial symptoms all occur in the ear.
In the distilled water (—B) cultures barley develops no ears. Rye
develops earsthe top part ofwhich develops withered glumes;over the
wholeoftheear noflowering occurs.Wheat produces earswith healthy
glumes;the anthers are atrophied and no grain develops. Oats produce
pollen grain whichis chiefly empty and the grain stagnates in development.
In the tapwater (—B) cultures barley bears hardly any grain. For
the other cereals there is no difference with the distilled ( + B ) sets
and they all produce healthy grain.
In the absence ofboron the highest vegetative and generative stages
are reached by Gramineae. This plant family as a whole holds a very
exceptional position when sensitiveness to boron deficiency is studied.
Allium cepa however, studied as a representative of another Monocotylidonous family appeared tobeinneedofboronat averylowstage
of development. With traces of boron it attained a fairly high development.
No clear distinction between Dicotyledons and Monocotyledons
with respect to boron requirements can be drawn.
A further investigation of the anatomy of the deficiency symptoms
in barley, rye, wheat and oats is on hand.
2.THEBORONCONTENTINPLANTMATTER
a. Estimations.
The great difference in the boron requirements of plant species
studied so far might be due to a constantly occurring difference in
content of boron among these species. The estimation of the content
19
of boron in plant material was therefore t a k e n u p . A preliminary notice
wasipublished in 1936 (a).
Tile analytical micro-method of B E R T B A N D and AGTJLHON X) (1914)
wasfollowed, b y means of which amounts of 0.1, 0.05, 0.01, 0.005,
0.001 a n d 0.0005 m g B can be estimated. The method is reliable for
these amounts. A serious drawback however is t h a t t h e intervals v a r y
so much in absolute value. An a t t e m p t to introduce smaller intervals
did n o t meet with success. The great advantage of t h e method is t h a t
it is BOvery sensitive for the low values, more sensitive t h a n a n y other
method existing. So small samples will suffice even for material with
a very slight content of boron.
The content of boron of t h e t a p w a t e r was estimated : in 2.5 Liter
0.001 m g boron could be detected.
All estimations were carried out on samples of 3 g d r y m a t t e r . The
determinations were always made in duplicate ;when checking was not
satisfactory the estimations were replicated. Generally however t h e
checking was good.
P l a n t material from different species a n d from various origin was
studied. P l a n t s were always cut a t soillevel in t h e early flowering stage
in order to exclude any influence of t h e occurrence of seed on t h e
résulte. The air d r y material was ground finely a n d t h e n dried to cons t a n t weight a t 105°.
I n Table 3 the amounts estimated in 1933 are presented. The d r y
weight is deemed t h e better basis for t h e calculation of t h e boron
content as t h e ash content of p l a n t m a t t e r is highly influenced b y soil
conditions.
Among t h e Dicotyledons the correlation between t h e behaviour in
boron-free solution a n d the a m o u n t of boron detected is slight. Contrar y t o w h a t might be expected Iberis umbellata with 16.7 p a r t s per
1
) Small tubes containing 2cc and marked a t 1,5 cc are manufactured. After
addition of Na 2 C0 3 a 3 g sample is ashed a t dull red heat in a porcelain dish.
The content of the dish is taken u p with 5 cc phosphoric acid and removed
t o a distilling flask. The residue is washed with 20 cc of methyl alcohol into the
flask. The content of the flask is distilled off into a crucible which has been
provided with 6drops of n. Na a CO s . Another 10cc of methylalcohol are distilled
off a n d t h e content of t h e crucible is evaporated t o dryness on a water b a t h .
4 drops of 10 n. HCl are added to the residue a n d t h e solution is washed ivith
distilled water into a 2 cc tube u p to the mark. A narrow stripe of curcuma
paper is slipped into t h e t u b e . After some 4 hours a t 30° when boron is present
the upper edge of the curcuma paper will have t a k e n on an orange red colour.
The length of this seam indicates the amount present, when it is compared
with standard tubes. These standards are provided with 5 drops of n. NajCO s ,
4 drops of 10 n. HCl and a range is prepared containing 0,1, 0,05, 0,01, 0,005,
0,001 and 0,0005 mg B as boric acid in distilled water. All tubes are filled u p
t o t h e m a r k a n d provided with a curcuma paper. By comparing with these
standards the estimation is carried out.
3
3
20
T A B L E 3.
BORON CONTENT I N VARIOUS PLANT SPECIES
Shoot
in 3 g dry w.
Plant species
Seed
parts per
million B
gash
indry
w.
in ash
0,1
0,295
33,3
339
0,1
0,434
33,3
145
mg B
in 3 g dry w.
mg B
0,04
g ash
0,113
parts per
million B
in dry
w.
in ash
13
354
(Lucerne)
(Swede)
0,075
(Mangold)
Pisum sativum
v a r . Mansholt
Pluherwt
v a r . Gele langstroo
....
Vicia sativa ( V e t c h ) . . .
(Field bean)
(Sugar-beet)
Trifolium r e p e n s
( W h i t e clover)
Solanum lycopersicum
( T o m a t o Ailsa Oraig)
25
0,07
0,07
0,03
0,01
0,07
0,05
0,07
0,06
0,06
0,307
0,326
0,398
0,339
0,456
0,358
0,409
0,35
0,581
23,3
23,3
10
3,3
23,3
16,7
23,3
20
20
228
139
75
29
156
139
169
171
103
0,06
0,561
20
0,06
0,05
0,05
0,619
0,631
0,422
20
16,7
16,7
0,005
0,01
0,006
0,01
0,005
0,117
1,7
3,3
2
3,3
1,7
43
0,01
0,134
3,3
75
0,01
0,231
3,3
43
107
0,04
0,129
97
79
118
0,01
0,12
0,03
0,155
10
194
128
0,05
0,155
17
323
11
0,009
0,132
3
68
16
0,007
33
0,09
0,129
48
31
25
0,001
0,063
0,3
15
27
7
17
13
19
19
0,002
0,081
0,7
25
0,001
0,001
0,061
0,105
0,3
0,3
16
9
13
3,3
310
83
(Candy tuft)
0,05
0,03
(Hairy Vetch)
Phaseolus vulgaris
D w a r f b e a n {brown
skin)
(spotted shin)
Trifolium i n c a r n a t u m
(Scarlet Clover)
Nicotiana tabacum . . .
Trifolium pratense . . .
( R e d clover)
Triticum vulgare
(Wheat)
Hordeum vulgare . . . .
(Barley)
S e c a l e céréale ( R y e ) . . .
Avena sativa (Oats)...
0,05
0,01
0,008
0,03
0,01
0,01
0,017
0,01
0,007
0,007
0,01
0,007
0,006
0,002
0,005
0,004
0,004
0,003
17
10
0,391
0,75
0,643
0,3
0,147
0,229
0,407
0,222
0,281
0,297
0,309
0,208
0,157
17
3,3
2,7
10
3,3
3,3
5,7
3,3
2,3
2,3
3,3
2,3
2
0,7
1,7
1,3
1,3
1
2,3
30
310
21
3
million dry matter ishigh and dwarf bean with 3.3 islow in content.
The coreals studied however are all lowinboron.
In asfarasseveral crops ofone species have been analysed, these
had gfown onvarious fields, andmoreover, varieties were different:
sothe differences incontent, sometimes very material, might be owing
to various causes. The largest differences were noted inpeas.
In order toinvestigate these points more fully, further experiments
were carried outin 1934. The same 4varieties ofpeas which in 1933
had been grown on various fields were grown now inthe experimental
field ofthe Laboratory for Mycology in Wageningen, aheavy clay soil.
The crops were estimated astothecontent of boron andtheresults
compared with thoseof1933are presented in Table4.
TABLE 4.
BORON CONTENT I N V A R I E T I E S OF PISUM SATIVUM
Variety
1933. Various fields
1934. One field.
23,3
23,3
10
3,3
19,3
19,3
12,3
3,3
Mansholt Schokker
I t appears that thevarieties follow thesame order asin 1933,although the highest values are slightly lower. Apparently the varieties
mask here any influence on the boron content asexercised by the soil.
The varieties ofSchokker andPlukerwt, equally high in content of
boron have been compared astotheir behaviour innutrient solutions;
for this purpose a similar kind of experiment is set up ashas been
carried outwith four varieties of garden pea (page 8).The results are
taken upinTable5.
TABLH 5.
DEVELOPMENT OF V A R I E T I E S OF PISUM SATIVUM I N N U T R I E N T
SOLUTIONS
Tapwater (-B)
Variety
Schokker
Plukerwt
Distilled water(-B)
Dry
weight
Transp.
Dry
weight
0,62 g
0,42 g
138 cc
100 cc
0,32 g
0,30 g
Transp.
72 cc
49 cc
Dry w. in tapwater—
dryw. indist.w.
0,30 g
0,12 g
3 gseed
mgB
number
0,005
0,01
8
13
When the size ofthe seed is taken into account, both varieties store
about equal amounts inthe seed and asmight beexpected they have
synthetisied in distilled water (—B) cultures about equal amountsof
organic matter. The greater amount ofmatter built upbySchokkeras
3
22
compared with Plukerwt in the tapwater (—B) cultures agrees well
with the stronger transpiration of the latter. In fact as the result of a
greater transport of water more boron may have been taken up from
the tapwater.
In order to study the influence of differences in soil on the content
of boron, in a same variety of wheat (Wilhelmina) grown on 6 different
fields and in a same variety of oats (Zegehaver)grown on 7fields, the
contentofboronwasestimated and theresults arepresented in Table 6.
T A B L E 6.
BORON CONTENTOFAGIVENVARIETYONVARIOUSFIELDS
Bin3gdryw.
0,009 mg
0,007 mg
0,006 mg
0,005 mg
0,004 mg
0,003 mg
parts p.million
in dryweight
Ashin3 g
dryweight
Wheat
(Wilhelmina)
3
2,3
2
1,7
1,3
1,0
0,295 g
0,183 g
0,211 g
0,244 g
0,262 g
0,161 g
parts p. million
onash
30
38
28
20
15
19
Oats (Zegehaver)
0,009 mg
0,006 mg
0,005 mg
0,005 mg
0,005 mg
0,005 mg
0,004 mg
2
3
1,7
1,7
1,7
1,7
1,3
0,325 g
0,221 g
0,230 g
0,246 g
0,183 g
27
27
22
20
27
—
—
0,221 g
18
The differences are appreciable, but still the highest content is low
compared with Dicotyledons.
Apparently Gramineae cannot take in a high store of boron.
b. Discussion.
How do the amounts presented agree with amounts found by other
workers?
Estimations of the amount of boron in plant matter are few. Recently however several investigations on this subject have been published. The amounts published will be discussed only as far as the
authors have analysed material from the same plant species as studied
by me and all will be recalculated as parts per million on the basis
of dry weight.
J A Y ( 1 8 9 5 ) , who analysed agreatvarietyofplant speciesand detected
23
boron in all material studied, states': „The plants which absorb the
leapt boric acid are Gramineae (wheat, barley, rice, rye); the amount
of boric acid estimated in the ash of these plants did not surpass 0.5 g
per kg (90 parts per million B)."
ÀGTTLHON (1910) whose method I have followed has analysed many
plant species, mostly trees. Only grain of wheat and oats can be compared with my estimations. He detected in wheat 15 and in oats 19.
These amount are over 50times as high as mine.
BRANDENBURG (1931) analysed according to the method of WILCOX
thefoliage ofsugarbeets. Hereports 46.SCHARRERand SCHROPP (1935)
have detected in the foliage of sugar beets grown in culture solutions
provided with boron 33 and 28. My estimations reached only 20, but
the plants analysed were grown in a field where heart-rot occurred,
thus on soil low in available boron.
BERTRAND, who after detecting boron in many plant specieswas the
firs* (1912) to point to the significance for agricultural practice of a
sufficient supply ofboron,hasvery recently taken up the subject again
(1936) and has analysed many agricultural plants. Allthe plant material studied was grown in the same garden so under the same soil
conditions.
In Table 7hisfigures are presented and compared with the amounts
found by me.
TABMS7.
PARTS PER MILLIOM BORON ON THE BASIS OF DRY WEIGHT
FOUND BY: BERTRAND AND DE WAAL AND BY LÖHNIS
Variety
Bertrand and de Waal
2,3
3,1
3,3
Trifolium incarnatum . . .
21,6
36,2
43
49,2
69,9
75,6
Löhnis
2,0,7
1,7
2,3, 2,3, 2,3, 3,3, 3, 2,3, 2,
1,7, 1,3, 1
23,3, 10, 3,3
3,3
17, 3,3, 2,7
33
10
20
When the figures in this table are studied it is very striking that the
amounts found in the cereals are very low and agree very closely with
thosefound byme.Forthe otherplant species BERTRANDand DE WAAL
find higher, sometimes much higher, values than I found. I t seems
probable that these plants were cultivated in soil very high in content
of boron. While the value in other plants increased the content of the
Gramineae remained low.
3
24
These data substantiate strongly the hypothesis that the exceptional
behaviour of Gramineae in a medium free of boron is due to a very
low content of boron in normal conditions.
Estimations of the boron content in the plant material of other species does not indicate their relative needs of boron. It is necessary to
grow the plants with known supplies of boron as has been done by
BRANDENBURG for sugar beets (1932).
3 . THE DISTRIBUTION OF BORON IN THE PLANTS
a. The content of youngand offull grownplant parts.
The fact that the initial symptoms of boron deficiency occur in the
meristematic parts ofthe plants giveriseto the question howthe boron
is distributed in the plants.
In 1934 the content of young and of full grown plant parts were
compared by the present author. Lucerne and tomato, both plants
with many lateral shoots, were used for the experiment. Young side
shoots (leaves and stems together), full grown leaves and full grown
stems of lucerne were dried and analysed separately. For tomato the
young shoots were separated from the full grown parts (leaves and
stems together). Table 8 gives the results.
T A B L E 8.
CONTENTOFBORONINYOUNGANDFULLG R O W NPARTS
p a r t s per million on
Plant parts
per 3g dry w.
dry weight
ash
Lucerne
young shoots
full grown leaves
full grown stems
412
260
221
0,1 mg
0,1 mg
0,05 m g
Tomato
young shoots
full grown shoots
young shoots
full grown shoots
0,06 mg
0,05 m g
0,05 mg
0,09 mg
20
16,7
16,7
30
152
78
104
154
A higher content of boron in the young parts was expected; the
experimental data however do not agree with this expectation. For
lucerne the only difference in value was found in the full grown stems
which are lower in content than young or old leaves. The results of
both sets of tomato lack uniformity.
25
The distribution in the cereals was studied as well. Just before the
flowering stage the ears were separated from the haulms and foliage.
The content of boron was estimated.
T A B L B 0.
D I S T B I B U T I O N OF B O R O N ON T H E BASIS O F D R Y W E I G H T I N
CEREALS
Ears
Haulms and foliage
Species
per 3 g
Barley . . .
Oats
Wheat . . .
0,01 m g
0,004 m g
0,007 m g
parts per mill.
3,3
1,3
2,3
per 3 g
0,002 mg
0,004 mg
0,006 mg
p a r t s per mill.
0,7
1,3
2
In oats and wheat none orhardly any difference occurred; in barley
however the ears were relatively high in content.
b. The content ofpollen grain of wheat.
In 193Ö it was observed that the anthers of wheat and the pollen
grain of oats were injured in the absence of boron. So itseemed worth
whileto analyse the pollen separately.
In collecting the pollen I followed the advice of Dr. H. Uittien and
proceeded in the following way.Haulmsofwheat onthevergeofblooming were cut and put up in wide low basins filled with water. The
haulms were lain nearly horizontally with ears erected in order that
the pollen could be shed on glass plates lain out along the sides of the
basins.Aftertwosunny days,any draught intheroom being prevented,
a fair amount ofpollen could be collected. It was dried and stored. The
samples of the pollen were not large enough to bedealt withinduplicate. Estimationsin duplicate however weremadein samples of glumes
of the same weight as the pollen.
TABLE
10.
CONTENT O F B O R O N I N P A R T S O F T H E F L O W E R O F W H E A T
CALCULATED ON T H E BASIS O F D R Y W E I G H T
p a r t of flower
actual boron
p a r t s per mill
Var. Juliana. I n 2,87 g
Pollen .
Glumes
0,03 m g
0,005 mg
10,4
1,7
Var. Vilmorin 27. I n 1,36 g
Pollen
Glumes
0,03 m g
0,0075 mg
22
5,5
3
26
The results show quite clearly that in wheat the pollen is materially
higher in content of boron than the further parts of the flower.
It was not possible to carry out a similar experiment with oats as
here only a very sparse shedding of the pollen can be induced.
c. Discussion.
In 1936 MCLEAN and HUGHES published an investigation on this
subject. They grew Vicia faba and Gossypium herbaceum in sand
supplied with a nutrient solution relatively highin boron and conclude
from their analytical data that the highest percentage per unit of dry
weight isin the leaves, increasing rapidly with the age of the leaf.
The petioles and the apices were approximately equal in percentage
content and had approximately double the stem concentration. The
roots had much the lowest concentration, only 0.07 ofthat ofthe stem.
These data explain the figures presented in Table 8 (page 24). By
separating the whole of the young shoots from the full grown parts no
higher content of the former sample was to be expected and the lower
contentofthe full grown stems agreeswellwiththefindings of MCLEAN
and HUGHES.
The deficiency symptoms of boron are very different from those
induced by a deficiency of most other elements. Generally the initial
injury causedby a deficiency occursinthe olderleavesand the growing
points are the last regions to show damage.
This difference in symptoms might be caused by a difference in the
rate of translocation between the main nutritive elements and boron.
The type ofrecovery in boron-starved plants seems to confirm the idea
that slowness of translocation is concerned. When these are supplied
withborondormantbudsatthe root neck develop and the injured parts
die off. The findings of MCLEAN and HUGHES who detected a higher
content of boron in older leaves point to a similar conclusion.
So it is possible that the fact of the occurrence of the initial injury
in the meristem is due to this slowtranslocation.Itistruethat MCLEAN
and HUGHES find a higher content of boron in the apex than in the
stem, but compared with the upper leaves it is lower. This does not
point to an especially high content.
These data however do not interfere with the finding of the high
content ofboroninthe pollen ofthe wheat. I t isevident that deficiency
symptoms willbemost severeinthose plant parts whichinthe presence
of boron are highest in content. So the absence of boron will involve
the non-formation of pollen grain which phenomenon again causes
an atrophy ofthe anthers.
In this connection the findings of SCHMUCKER (1934) are very interesting, who has noted that the pollen of a tropical Nymphaea will
only germinate in experimental conditions when boron is supplied.
27
I n the ash of the pistil fluid he could detect 1 per cent of B 2 0 8 . He
studiedthe pollenofmany plant species and observed that in many of
th£m boron was essential for the germination and for a normal growth
ofithe pollen tube.
Jtisquiteconceivableitwillbethe study of pollen which may elucidatethe veryfundamental part boronplaysinthe biochemical processes.
4 . THE BOLE OF BORON IN THE MINEBAL NtTTEITION
a. The influence of boronand calcium onplant development.
BBENCHLEY and WABINGTON proved definitely in 1927 that boron
cannot bereplaced by any other element. They suggest however: „that
boron might act indirectly by influencing the intake or utilization of
other nutritive elements that are needed in larger proportions.In that
case the characteristic symptoms of boron deficiency would occur if
the element in question were absent even in the presence of boron in
the. culture solution." They put Vicia faba to the test in a set of modified „Rothamsted solutions", where one of the elements had been
omitted. In the absence ofany oftheelements,calciumexcepted, plants
made a good initial development. When calcium however was omitted,
the plants turned black and died very rapidly. With a very low supply
of calcium and no boron injury in the tips and whithering of the stems
occurred at an early stage of development; if boron was supplied the
plants developed fairly well and only black edges at the leaves could
be observed. This might imply a toxicity of the food solution, neutralized by the presence of calcium. To test this hypothesis the bean
plants were grown in solutions of individual food salts in the concentrationasusedinthe,,Rothamstedsolution''withandwithoutasupply of boron. All of the salts appeared to have a toxic action except
CaSO«. When this salt was supplied: „growth was better and more
rapid at first than in the complete nutrient solution and signs of boron
deficiency set in several days earlier than in the latter case. It was
only later when the absence of other food salts made itself felt, that
theoalciumplantsfellbehind the complete nutrient set in development,
but to the end those with boron were strikingly good, and those without showed all the signs of boron deficiency most markedly. The final
conclusion deduced from these experiments was: calcium is necessary
to counteract the harmful action of the other food salts and without
boron the calcium isnot fully utilized.
In 1933 the present author tested whether the same results would
be obtained when Medicago sativa was used as experimental plant.
The „Rothamsted solution" x)wasusedandtheexperimentlasted from
l
) K N 0 3 1g; K H 2 P 0 4 0,6 g; NaCl 0,5 g; C a S 0 4 0,5 g; M g S O 4 0 , 5 g ; F e C l 8
0,p4 g; distilled water 1000 g.
3
3
28
May 23rd to June 22nd. Germination was effected in moist sand and
the following experimental set was put up in duplicate:
1. distilled water; 2. + 0,5 parts per million H 3 BO a ; 3. + 0,05%
CaS0 4 ; 4. + 0,5p.p.m.H 3 B0 3 + 0,05%CaS0 4 ; 5.Complete Rothamsted solution (containing 0,005% CaS0 4 )no boron; 6. id. + 0,5p.p.m.
H 3 B0 3 ; 7. id. (containing 0,05% CaS0 4 ) no boron; 8.id + 0,5 p.p.m.
H 3 B0 3 .
The variations in content of CaS0 4 in the complete solutions were
set up becauseit had been noted that the lower content was sometimes
more favourable. Fig. 28 where 1—6 are presented show the results.
In 1and 2,both cultures without boron, the growth wasvery poor and
only four chlorotic leaves had developed. In 3 end 4where calcium
was present the development ofthe shoots and roots was much better;
3 showed signs of boron deficiency after two weeks but in 4 where
calcium and boron had been supplied, the development after a month
wasquite ashealthy and profuse asinthe complete nutrient solution 6.
In the complete solution without boron 5 signs of deficiency occurred
at the same moment asin 3.
Apparently the phenomena noted in Vicia faba could be perfectly
reproduced in lucerne.
It appeared however thattheseresultsneededanother interpretation.
As I was well acquainted with the signs of nitrogen deficiency in
lucerne and had often observed that not morethan 3or4leaves would
developinthe absence ofnitrogen, the profuse development when only
calcium and boron had been supplied, pointed to the availability of
nitrogen from accidental source. Doubtlessly the good growth had to
be explained by some stray infection with Bact. radicicola. In fact I
had not noted any nodules on the roots of these plants, but an overgrowth of parenchyma had occurred on the taproot which might have
masked small nodules. At all events the experiment needed repeating
under sterile conditions.
In 1934the germination waseffected in a petri dish ontapwater agar
and the plantlets were put up in sterilised culture vessels containing
similar culture solutions as in 1933 (all in the low concentration of
CaS0 4 ). Nofurther precautions for preventing the infection with Bact.
radicicola were taken; the results show that by this method a stray
infection could be prevented. The experiment was run from May 28th
to June 16th. Fig. 29 shows the results. There is no difference in the
development of the shoot in the + calcium set (3 and 4) andthe sets
without calcium (1and 2).Theroot system howeverisbetter developed
in the presence of calcium than in the absence and the development is
lowest when both calcium and boron are lacking. Both elements seem
to be essential for growth. The development of 4{-\- Ga + B)falls here
very far behind the development in the complete culture medium with
29
börott supplied (5). It is quite evident that the striking growth in the
-r C* + B set in 1933 is to be ascribed to an assimilation of nitrogen
due to Bact. radicicola. I did not succeed as yet in reproducing the
profuse growthby meansofinoculation ofasterile culture. Doubtlessly
it can be done but after one failure time was lacking.
In 1936 a similar experiment was run, while sterile conditions were
kept up till the end. Lucerne was cultivated in large test tubes (20 cm
high).The solutions used were: 1. 0,005% CaS0 4 + B ; 2. + 0,005%
CaSOa; 3. -f CaCl2 equimolar with 1; 4. + B ; 5. distilled water, 6.
+ 0,05% K H 2 P 0 4 (the concentration as supplied in the complete
solution).
Fig. 30showstheresults which agree very well with those of former
experiments. In all of the test tubes hardly any growth of the shoots
occurred. The growth ofthe roots was by far the best in + Ca + B (1)
and least in no Cano B (5). 2and 3both provided solely with calcium
show about the same length of root with stubby laterals, due to the
lack of boron. When calcium was lacking and boron supplied (4) the
length growth was slight. The last tube with K H 2 P 0 4 shows the toxic
nature of the one salt solution.
Both calcium and boron appear to be essential for the growth of
the root system. When both elements are lacking growth is poorer
than in the absence ofone of them.
Further tests were made, whether similar results would be obtained
in the case of non-leguminous plants. Solanum lycopersicum was
chosen,asNIGHTINGALE and al. (1931)had described anapicalinjury in
calcium-starved plants, which seemed to bear a great resemblance to
signB of boron deficiency. The plants were grown in the Rothamsted
solution. When CaS0 4 was omitted from the nutrient solution, in
fact plants were affected in much the same way as when boron was
lacking. In both cases the growth in the apex came to a standstill and
the small leaves took on a greyish or violet hue. The older initially
normalleaves grew brittle,the petioles as wellasthe individual leaflets
turned downward and the leavestook on a yellowish shade.In calciumdeficient cultures the lateral roots however developed better than in
theboron-deficient solutions.Whenbothcalciumandboronwere absent
the damage in shoots and roots occurred at a still earlier stage
of development. Apparently as deficiency of calcium and of boron
affect the same parts ofthe plant, symptoms increase in severity when
both are lacking. Fig. 31 shows the results.
Moreover tomato plantlets have been grown in solutions of the individual food salts in distilled water, viz. in 0,05% CaS0 4 and H 3 B0 3
0,5 parts per million. The experiment was run from May 29th till
Jude 23rd. Asis shown on Fig. 32a andb the development ofthe shoot
is very slight in all of the cultures. The roots however develop better
3
3
30
in t h e absence of calcium t h a n in t h e absence of boron. The developm e n t ispoorer when b o t h elements are lacking.
The results obtained with t o m a t o agree very well with those obtained with lucerne.
b. Discussion.
Apical injury caused b y calcium starvation is described for orange
tree ( R E E D a n d H A A S 1923), Vicia faba ( B R E N C H L E Y a n d W A R I N G T O N
1927), t o m a t o (NIGHTINGALE a n d al. 1931), tobacco {MCMTXRTREY
1933), p o t a t o (VAN S C H R E V E N 1934 6). Nightingale a n d al. could
detect int o m a t o plants showing apical s y m p t o m s ofcalcium starvation
a n appreciable a m o u n t of calcium in t h e older leaves. MCMTTRTREY
describes in tobacco with apical injury after supply of calcium as t y p e
of recovery t h e development of suckers. B o t h phenomena point a t a
slow translocation of calcium.
The present author could observe t h a t deficiency of calcium caused
a similar t y p e of apical injury in t o m a t o as t h a t due t o lack of boron.
The young roots of lucerne a n d t o m a t o answered with poor growth
in t h e absence of either calcium or boron. The t y p e of recovery in t h e
shoot wasvery similar for calcium or boron.
B o t h boron a n dcalcium appear t o beessential forgrowth. According
to SOMMER a n d S O R O K I N (1929) in t h e absence of calcium t h e normal
course of mitotic division isinterfered with.
Slow translocation is probably associated with lack of calcium just
as with lack of boron.
The fact t h a t t h e lack of either element affects t h e p l a n t in m u c h
the same w a ymakes i t evident t h a t t h e absence ofb o t h will aggravate
t h e injury.
I t is suggested t h a t t h e t y p e of injury m a y be understood on this
basis a n dt h a t there isnoneed t o suppose a n yspecialinfluence of boron
on t h e intake of calcium.
I t issuperfluous t o mention t h a t under field conditions t h e presence
of calcium might influence t h e availibility of boron. This problem
however hast o be attacked with t h e methods oft h e soil scientist.
5. A POSSIBLE SOURCE OF BORON
I n which form is boron available t o t h e plant?
B R E N C H L E Y a n d W A R I N G T O N (1927) succeeded in growing healthy
plantsinmediawhereboron wassupplied asso-called insoluble borates.
Tourmaline constitutes a p a r t of m a n y sands. About 10per cent of
this mineral consists of B 2 0 3 . The boron in this mineral is considered
as insoluble, t h u s unavailable for living organisma.
31
BATON (1935) in a study on boron injury reports that plants grown
experimentally in a finely powdered tourmaline mineral did not develop any symptoms of boron injury.
Professor EDELMAN invited me to test the effect oftourmaline when
supplied as the only source af boron.
Phaseolusvulgaris(Runnerbean)was used as one of the experimental plants and 0,013°/0 finely ground tourmaline was added to the
nutrient solution prepared with distilled water. The experiment was
setup on June 18th. On July 3rd the plants without boron had stagnated in growth after the production ofapair ofprimary leaves.Fig. 33
shows the results attained on August 1st. The plant provided with
tourmaline bore several buds and one pod, its root system was sound
and no signs of boron deficiency could be detected.
In asameway0,025%oftourmaline was added to the nutrient solution of tomatoes. Here again tourmaline satisfied the boron requirements of the test plants and these plants were as well developed as
plants supplied with boric acid.
These experiments are not meant to prove that tourmaline can be a
source of boron under field conditions. They merely prove that plants
may be a highly sensitive indicator of traces of boron, traces supplied
here by a mineral considered insoluble.
6. SUMMARY
Medicagosativa wasfound to behighlysensitive to boron deficiency.
Phaseolus vulgaris in the varieties tested (a runner bean and a
dwarf bean) appeared highly sensitive.
8 varieties tested of Pisum sativum were sensitive to boron deficiency. Wonder van Amerika previously reported as insensitive, showed
deficiency symptoms at an earlier stage of development than the other
varieties. The rate of transpiration in boron-free solutions prepared
withitapwater did not correlate with the amount of organic matter
synthetisied. So the boron requirements of the varieties tested was
different.
Iberis umbellata when set up in early spring produced no flowers
in the total absence of boron; when tested later the plants flowered.
In solutions without supply ofboron and prepared with tapwater some
ripeseedswereproduced. In the total absence ofboron the root system
though small, did not show any injury.
Vicia villosa in tapwater cultures deprived of boron reached a fairly
highvegetativedevelopment. The initial injury occurred in full grown
leaves.
Hordeum vulgare did not shoot its ears in distilled water cultures
deprived of boron. In tapwater cultures without supply of boron ears
and haulms were well developed, but hardly any grain was produced.
3
3
32
Seeale céréale in the total absence of boron developed ears the tops
of which bore withered glumes;over the whole of the ear no flowering
occurred. In tapwater cultures without supply of boron healthy grain
was produced.
Triticum vulgare in distilled water cultures deprived of boron produced atrophied anthers and no grain developed. In tapwater without
the supply of boron the development was normal.
Avena sativa produced in the total absence of boron full grown anthers;the pollengrainshoweverwerechiefly empty. The grain stagnated in development. In tapwater cultures without any boron added
the development was normal.
Alliumceparequiredboron at anearlystageofdevelopment. For the
production ofhealthyflowers and seed from bulbs boron was essential.
TheCerealshave alowcontent ofboroninthe plant andinthe grain.
Soil conditions may influence the amount, but even the highest values
attained are comparatively low.
Among the Dicotyledons the correlation between the behaviour of
various plant speciesin boron-free solutions and the amount of boron
detected in the plant matter is slight.
Young shoots of Medicago sativa and Solanum lycopersicum were
no higher in contentthan the older parts. Full grown stems of lucerne
were lowest in boron content.
The ears at the moment offlowering of Triticum and Avena had the
same content of boron asthe haulms with the foliage. In Hordeum the
content of the ears was higher than of the other parts.
The pollen grain ofwheat had a materially higher content of boron
than the total plant.
Calciumdeficiencycausesthesametype ofinjury asboron deficiency.
The fact that the lack of either element affects the plant in much
the same way makes it evident that the absence of both elements will
aggravate the injury.
Tourmaline may provide a plant with boron when no other source
of boron is present.
7 . CONCLUSIONS
As far as it has been tried experimentally, boron is an essential
element for all Angiosperms.
The constantly occurringlowcontent ofboroninCerealswhen grown
under field conditions explains the profuse development of these plant
species when grown in a culture medium devoid of boron.
The high content of boron in the pollen grain of wheat explains the
occurrence of deficiency symptoms merely in the anthers.
There is no need to suppose any,special influence of boron on the
intake of calcium by the plant.
33
ACKNOWLEDGMENTS
Thanks are due to Professor J. HTTDIGfor providing the opportunity
of carrying out this research in the Laboratorium voor Landbouwsohaikunde and in his private Laboratory.
To Professor A. H. BLAATTW for letting me dispose of the conveniences of the Laboratorium voor Plantenphysiologisch Onderzoek
in collecting the pollen.
To Professor H. M. QTTANJEBfor the opportunity of growing plants
in the experimental field of the Laboratorium voor Mycologie.
To Professor J. A. HONING for the fact that the microphotos could
be made in the Laboratorium voor Erfelijkheidsleer.
To Ir. J. D. KOESLAG for the supply of plant matter from field
crops.
Special thanks are expressed to Miss Maud Williams for her helpfulness in correcting and improving the English in this paper.
Wageningen, June 1937.
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Mc H A B G U E , J . S. and CALFEE, R. K., 1933. Further evidence t h a t boron is
essential for t h e growth of Lettuce. Plant Phys., 8,p . 305.
Mc LBAN, R. C. and H U G H E S , W. L., 1936. The q u a n t i t a t i v e distribution of
Ie ' boron inVicia faba a n dGossypium herbaceum. Ann. Appl. Biol., 23,p . 231.
MCMUBTBEY, J . E „ 1929. Theeffect of boron deficiency on t h e growth ofTobaoco plants in aerated and unaerated solution. J . Agric. Res.,38,p . 371.
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Dapt; of Agric. Techn. Bull. 340.
M E S , M.G., 1930. Fisiologiese siektesimptome v a nT a b a k . Diss. Utrecht.
M E S , M.G., 1930. Physiological disease symptoms of Tobacco. P h y t o p . Ztschr.
2, p . 593.
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3
3
36
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WABINGTON, K., 1933. The influence of length of day on the response of plants
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E X P L A N A T I O N OF P L A T E S
Alii plants photographed have been grown in nutrient solutions prepared
either with tapwater or with distilled water and with or without a supply of
borOn. The individual t r e a t m e n t is printed under t h e figures.
Fig.
.,
,,
,,
,,
„
,,
,,
,,
,,
,,
,,
,,
,.
,,
,,
,,
,,
,,
„
,,
,',
,,
.,
„
,,
,,
„
,,
,,
,,
,,
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
Beta vulgaris. Sugar beet.
Trifolium repens.
Trifolium campestris.
Trifolium incarnatum.
Lycopersicum esculentum. Var. William Gopelcmd.
Nicotiana t a b a c u m . Var. atropurpurea.
Vicia faba. Field bean.
Grape grown from cuttings Var. Frankenthaler.
Medicago sativa. Var. Provencer lucerne.
Phaseolus vulgaris. Runner bean. Var. Prinsesseboon.
Phaseolus vulgaris. Dwarf bean. Var. Bruine boon.
Grown from May 27th to J u n e 15th.
12. I d . grown from September t o middle of December.
13. Pisum sativum. Var. Kroonerwt.
14. Vicia villosa. Winter Vetch.
15. Iberis umbellata. Candy tuft. Grown from April 9th to J u l y 8th.
16. Secale cereale. Winter Rye in flowering stage.
17. Triticum vulgare. Winter wheat. Var. Wilhelmina.
18. Pistil and stamens of wheat cultivated in the absence of boron.
Magn. 6 x .
19. Id. stamens. Magn. 6 x .
20. Pistil and stamens of wheat cultivated in the presence of boron.
Magn. 6 x .
2 1 . Avena sativa.
22. Stamens of oats cleared with chloral hydrate and stained with iodine.
1 t a k e n from plant supplied with boron, 2 grown in the absence
of boron. Magn. 13 X.
23. Stamen from oats grown in the absence of boron. Treatment as 22.
Magn. 13 x .
24. Pollen grain from oats suplied with boron. Treatment as 22. Magn.
160 x .
25. I d . from oats grown in the absence of boron. Magn. 150 x .
26. Allium cepa. Var. Rijnsburger. Plants grown from seed.
27. Id. Plants grown from bulbs.
28. Lucerne, 1—4 grown in one salt solutions and 5 and 6 in Rothamsted
nutrient solution. No sterilisation of nutrient medium.
29. Lucerne, 1-4 grown in one salt solutions and 5inRothamsted nutrient
solution. Sterilisation of nutrient medium.
30. Lucerne grown in one salt solutions under sterile conditions.
31. Tomato plants grown in Rothamsted nutrient solution in the presence
and in the absence of calcium and boron.
32a and b . Tomato plants grown in one salt cultures in the presence or
absence of calcium and boron.
33. Phaseolus vulgaris. To the culture on the right 0,01% tourmaline has
been added.
CONTENTS
page
1. Signs of boron deficiency.
a. Introduction
3
b. Plant species for which the essential nature of boron had
been definitely established by former authors
5
c. Plant species for which conclusive evidence was lacking . 6
d. Plant species which gave conflicting results as reported by
various authors
8
e. Plant species for which boron wasreported asunessential . 10
ƒ. Discussion
11
2. The boron content in plant matter.
a. Estimations
b. Discussion
3. The distribution of boron in the plant.
a. The content of various plant parts
b. The content of pollen grain of wheat
c. Discussion
4. The role of boron in the mineral nutrition.
a. The influence of boron and calcium on plant development
6. Discussion
5. A possible source of boron
18
22
24
25
26
27
30
30
6. Summary
31
7\Conclusions
32
Acknowledgments
Literature cited
Explanation of plates
33
34
37
Fig. 1
Tapw.— B
Dist.w.—B
Dist.w.+ B
?r
Fig. 2
Tapw. — B
water
Dist.w. —B
;
Dist.w.+ B
——— —
Fig. 3
Tapw.— B
Dist.w.— B
Dist.w. + B
Fig. 4
Tapw. — B
Dist.w. — B
Dist.w. + B
Ort HB
Fig. 5
Tapw. — B
Dist.w. — B
Dist.w. + B
Fig. 6
Tapw.
—B
Dist.w.
—B
Dist.w.
+B
Fig. 7
Fig. 8
Tapw. Dist.w.
—B — B
Distw.
+B
Dist.w.— B
Dist.w. + B
Fig. 9
Tapw.— B
Dist.w.— B
Dist.w. + B
Fig. 10
Tapw.
—B
Dist.w.
— B.
Dist.w.
+B
tó^H
Fig. 11
Tapw.
—B
Dist.w.
—B
Dist.w.
+B
Fig. 12
Tapw.
Dist.w.
Dist.w.
—B
—B
+B
water
Fig. 13
Tapw.
—B
Dist.w.
—B
Dist.w.
+B
Fig. 14
Tapw. — B
Dist.w. — B
Dist.w. + B
Fig. 15
Tapw
—B
Fig. 16
Dist.w. + B
Dist.w. — B
Fig. 18
Dist.w.— B
Dist.w. + B
F i g . 18
F i g . 19
Dist.w. — B
F i g . 20
Dist.w. — B
Dist.w. +1
F i g . 21
Tapw.
—B
Dist.w. Dist.w.
—B
+ B
Fig. 22
Fig. 24
Dist.w.
Dist.w.
+B
—B
Dist.w. + B
Fig. 23
Fig. 25
i
I
Q ©
w ™
Dist.w.—B
Dist.w.—B
Fig. 26
Tapw. — B
Dist.w. — B
Dist.w. + B
Fig. 27
Tapw.
—B
Dist.w.
—B
Dist.w.
+B
1933
Fig. 28
2
I
— Ca
—Ca
—8
+B
3
4
+Ca
5
+Ca
—'B + B
Roth.
—B
6
Sol.
+B
Fig. 29
I
2
3
4
J
— Ca
— Ca
+ Ca
+B
+ Ca
+B
Roth. Sol.
— B
— B
+B
CxS ChS -JXCÎ S
:;. i
KP
Fig. 30
1
2
Ca(S04)2 Ca(S04)2
H3B03
+ Ca.+B
y
CaCl,
_Ca+B
d
5
H 8 B0 3
Dist.w.
+ t o _ B
6
KH 2 PO,
_Ca _ B
Fig. 31
iFig. 32a
+ Ca + B
Fig. 32b
-Ca — B
-Ca + B
-Ca — B
Fig. 33
Dist.w.
—B
Dist. w.
+B
Dist.w.
Tourmaline