STUDIES IN SEEDS AND FRUITS
STUDIES IN
SEEDS AND FRUITS
An Investigation with the balance
X BY
Hf B? GUPPY, M.B., F.R.S.E.
'The old is still the true." AUSTIN DOBSON.
LONDON
WILLIAMS AND NORGATE
14 HENRIETTA STREET, COVENT GARDEN, W.C.
1912
I DEDICATE THIS BOOK TO THOSE WHO
SO KINDLY APPRECIATED MY PREVIOUS
WORK AMONGST THE PLANTS. IN
GRATITUDE I HERE GIVE
THEM OF MY BEST
PREFACE
IN the preparation of this work my indebtedness lay in many
directions. The circumstances of my life enabled me to
devote all my time to it, a very important condition for
extensive original investigation. Then, in connection with
West Indian plants, with which these pages are principally
concerned, there was always in my hand Grisebach's Flora
of the British West Indian Islands, the only accessible
general work on the plants of those regions. Most of the
German botanical works consulted were in English dress ;
but amongst the exceptions was Nobbe's Handbuch der
Samenkunde, a work essential for me to be familiar with,
and I am deeply indebted to my wife for her assistance in
mastering its contents.
Then, again, as I rambled about on the coasts and in the
inland woods of the West Indian Islands, or sat quietly
working in my study at home, or lay in my cabin during
the voyages to and fro across the Atlantic, ideas came floating
through my mind which often took solid form and developed
into lines of investigation before unsuspected. Some of them
may have been echoes of my reading. For instance, from a
recent re-perusal of Professor F. W. Oliver's address to the
Botanical Section of the British Association in 1906, I find
that I have unwittingly supplied answers to more than one
of his suggestive queries. But there are other ideas that
cannot be explained in this fashion, and they also have
solidified and stand out boldly in the following pages. Amongst
the sources to which I owe much, they are not the least.
viii STUDIES IN SEEDS AND FRUITS
Whilst arranging the results of my observations, the difficulty
of establishing a nexus between them soon became apparent,
One thing led to another in an irregular manner, the new line
of inquiry being often determined by some accidental indication,
or by some inconsistency in the results of experiments. Per-
ceiving that it would not be conducive to method to follow
the order of inception of the several inquiries, I devised the
plan of arranging the materials to be now described. The
shrinking and swelling processes of seeds were first discussed
until the question of permeability or impermeability was
raised so frequently that the matter had to be dealt with
before further progress could be made. In its turn, the
subject of permeable and impermeable seeds was treated on
its own ground until the question of their hygroscopicity
demanded investigation. So also the matters relating to the
proportional weight of parts of fruits, and to the connection
between the seed-number and the fruit-weight, were discussed
until the disturbing influences of the abortion of ovules and
the failure of seeds became so obvious that an inquiry into
their nature was necessitated.
Amongst the other difficult questions that presented them-
selves in this inquiry was that relating to the unit of weight
most suitable for seeds and fruits. It was soon found, how-
ever, that the grain was by far the most fitting for my purpose,
and it was accordingly adopted. The grain is not only one
of the most ancient and one of the most extensively employed
units of weight for small objects (such as precious stones),
but it is Nature's primitive suggestion. Seeds of small size
are in use as weights in the East at the present day ; and
other persons besides myself must have been at times so
circumstanced that they had to extemporise a balance and
employ grains of rice as weights. This choice has enabled me
to avoid the multiplicity of terms inseparable from most
systems. Whether it happens that 60,000 grains go to weigh
down a green coco-nut, or that 6000 Juncus seeds go to
weigh down a grain, no other term of weight need be used.
PREFACE
IX
Though in a few instances the grains have been converted
into grammes, the use of percentages in stating the results
in the great majority of cases will enable the reader to be
largely independent of the unit of weight employed.
My original plan was to include in this volume the results
of my observations on the distribution of seeds by currents in
the West Indian region, and through the agency of the Gulf
Stream drift. However, this idea has been abandoned for at
least two reasons. In the first place, such materials would have
greatly added to the size of a book already large ; and, in the
second place, since the subject was concerned with quite
another matter, it could very well be treated in a separate
volume. Though much of the work done in this direction
has been put into shape, it has been decided to defer its
publication ; and in the meantime I hope to considerably add
to my facts relating to the occurrence of West Indian seed-drift
on the Atlantic shores of Europe. This is the continuation of
a study commenced by me in the Pacific about thirty years
ago, and taken up from time to time in different parts of the
tropics, many of the results being given in my book on Plant-
Dispersal (1906), and in various papers enumerated in the list
given on page xiii of that work.
I would take this opportunity to ask any reader who is inter-
ested in the occurrence of West Indian seeds on the west coast
of Europe or on the neighbouring islands to communicate
with me. Having studied the question during four winters in
the home of the drift, in different parts of the West Indies, I
wish to make as complete as possible the materials relating to
this side of the Atlantic. These seeds are frequently stranded
on the beaches of Europe, between the North Cape and the
Straits of Gibraltar. Residents on the west coasts of Scandi-
navia, Scotland, Ireland, England (south-west), France, Spain,
and Portugal, and on the off-lying island groups, must often
come upon these stranded seeds. The great majority of the
seeds thus picked up do not come into the hands of any
person who has studied the subject. Some of those who read
x STUDIES IN SEEDS AND FRUITS
these pages may be in a position to assist me in this inquiry,
either by taking up the search themselves, or by lending me,
for purposes of specific determination, any seeds in their
possession, or by supplying information concerning collections
of these seeds in the hands of private persons or in museums,
or in giving me references to any literature (whether in the
press or in scientific publications) dealing with the matter.
Any materials left in my possession would subsequently, with
the donor's permission, be distributed amongst the large
museums.
H. B. GUPPY, M.B.
" ROSARIO," SALCOMBE,
SOUTH DEVON, January 31, 1912.
CONTENTS
CHAP. PAGE
1. THE HISTORY OF THE INVESTIGATION .... I
2. THE THREE CONDITIONS OF THE SEED . . . 1 8
3. THE IMPERMEABILITY OF SEEDS AND ITS SIGNIFICANCE . 56
4. PERMEABLE AND IMPERMEABLE SEEDS .... 69
5. THE GROUPING OF SEEDS ACCORDING TO THEIR PERMEA-
BILITY OR IMPERMEABILITY ..... QO
6. ADDITIONAL EVIDENCE ON THE CONTRAST IN BEHAVIOUR
BETWEEN PERMEABLE AND IMPERMEABLE SEEDS . 114
7. HYGROSCOPICITY ........ 147
8. A LAST WORD ON THE HYGROSCOPICITY OF SEEDS . l8o
9. THE REGIME OF THE SHRINKING AND SWELLING SEED . 187
10. THE FATE OF SEEDS AS INDICATED BY THE BALANCE . 225
11. A CLUE TO THE HOMOLOG1ES OF FRUITS . . . 24!
12. THE HOMOLOGIES OF FRUITS AS REVEALED IN THE DRYING
PROCESS ......... 258
13. THE DEHISCENCE OF FRUITS ...... 273
14. THE PROPORTION OF PARTS IN FRUITS .... 293
15. THE RELATION BETWEEN THE NUMBER OF SEEDS AND THE
WEIGHT AND SIZE OF THE FRUIT . 330
xi
xii STUDIES IN SEEDS AND FRUITS
CHAP.
1 6. THE ABORTION OF OVULES AND THE FAILURE OF SEEDS
17. SEED-COLORATION .......
1 8. THE WEIGHT OF THE EMBRYO ....
19. THE REST-PERIOD OF SEEDS .
20. THE COSMIC ADAPTATION OF THE SEED .
APPENDIX . . . . . . . .
INDEX
STUDIES IN
SEEDS AND FRUITS
CHAPTER I
THE HISTORY OF THE INVESTIGATION
THIS investigation commenced as a study of the rest-period
of seeds ; but its course has often been determined by small
indications, the balance and the oven, aided by a sharp knife
and a pocket-lens, being the only means of research employed.
From the beginning it was for me a leap in the dark, since A leap in the
although investigators far abler than myself have written on ar '
the subject, there was little that seemed to offer a clue. Need-
ing some firm ground to stand upon with reference to fruit-
maturation and as regards the behaviour of the ripening seed,
and of the seed entering the rest-period, I turned to the most
authoritative works at my disposal, those of Goebel and Pfeffer.
From the pages of the Organography of Plants I learned that
the biology of the ripening fruit has hitherto scarcely received
attention (English edition, 1900-5, ii. 570-571) ; and when
consulting the Physiology of Plants with reference to the assump-
tion of impermeability by many seeds when they enter the
rest-period, I learned that the means by which the power of
resistance to drying is gained and the changes which cause its
loss are quite unknown (English edition, 1903, ii. 253).
I suppose the reason why many have not ventured in this
field is that there seemed no near prospect of obtaining tangible
and serviceable results. It has in truth been for me like an
Suggested
by previous
studies of
vivipary in
the Pacific.
The first
clue.
2 STUDIES IN SEEDS AND FRUITS
exploring voyage in a little-known ocean where the lead rarely
reaches the ocean's floor and " two thousand fathoms and no
bottom" is a frequent record. Just as during my sojourn in
the Pacific, the study of seed-buoyancy led me finally to discuss
the history of the whole flora of those islands, so this work has
been developed by slow degrees from my original observations
on the vivipary of plants in that region. The possibility of
all seeds being able to germinate on the plant presented itself
to me whilst observing on the Hawaiian lava-plains the be-
haviour of the seeds of Gullandina bonducella in the green
pod ; and this led me to the study of the rest-period of seeds.
But at first, to employ another simile, it was like a plunge
into the depths of a primeval forest. My path branched off
in a hundred different ways, tracks crossing and re-crossing
and often leaving me in some tangled jungle. Instead of
simplicity I found complexity, my inquiries taking me in all
kinds of unexpected directions, the difficulty lying in the choice
and in knowing when to retrace my steps. However, ulti-
mately I emerged from the forest at a place far distant from
where 1 entered, and have now the story of my experiences
to tell.
Perhaps I shall best explain the discursive character of this
work and the variety of subjects handled, if I state briefly the
various stages of my investigations. When observing the
maturation and germination of the seeds of Guilandina bondu-
cella in 1897 in Hawaii (Observations of a Naturalist in the
Pacific^ ii. 191), I noted that in germinating these stone-like
seeds assumed again the appearance of immaturity. The soft,
moist seed from the green unopened pod and the soft, swollen
seed on the eve of germination were both of them two or
three times the size of the normal resting seed, and might at
first sight be mistaken for each other. Surely, I argued, it
would be possible, in the case of the seeds of this and other
leguminous plants, by subjecting the pod on the plant to
humid conditions, to dispense with the rest-period
warm,
altogether, and to bring about the germination on the plant of
THE HISTORY OF THE INVESTIGATION 3
the large, soft, seemingly immature seeds before the drying and
shrinking process that ushers in the rest-period begins.
However, nearly ten years passed by before I saw my way
to attacking the problem that first presented itself almost as
in a dream during my sojourn in Hawaii. Here again it was
from the same plant (Guilandina bonducelld] that I obtained
my clue. Whilst observing in December 1906 this plant in
immature fruit on the beach of St Croix (Danish West Indies),
it occurred to me that there was at least one indirect way of
approaching the problem other than by carrying out an experi-
ment more visionary than practicable in its nature. So I
placed a number of the soft unripe seeds in wet sand, believing
that under such moist conditions they would not go through
the usual shrinking and hardening process. The experiment
was completed at Black River, Jamaica ; and after five weeks
I found that the seeds had retained their original size and
consistence. The shrinking process had thus been deferred ;
whilst in the case of seeds gathered at the same time and
allowed to dry in the air the seed had been reduced by shrink-
ing to about a third of its original weight.
Just at this time, whilst studying the floating seed-drift of
the Black River, I noticed that the shrinking process was con-
sistently shirked by some of the river-side plants, the seeds, The mdica-
after falling into the water, rapidly passing on into the germin- seed^drift
ating state whilst still afloat. They were hot viviparous plants, Jamaica,
but possessed seeds with soft coverings which would not pro-
tect the embryo against injurious desiccation, the result being
that unless the fallen seed found itself in moist conditions and
germinated quickly, its chance of reproducing the plant was
gone. Perhaps the most interesting of these plants were
Crudya spicata and Moronobea coccinea, the one leguminous,
the other guttiferous. The first is known as the Kakoon
(Cacoon) tree, from the resemblance of its seeds to those of
Entada scandens, a plant bearing the same name. The second
is the Hog-gum tree.
It was, however, an observation on the seeds of Abrus
Other
indications.
Working
hypotheses.
4 STUDIES IN SEEDS AND FRUITS
precatorius that gave direction and method to my inquiries.
Noticing that the large, soft, unripe seeds of the green un-
opened pod were three times the size and double the weight of
the normally contracted hard seeds of the dehiscing pod, I
found that a large, soft, unripe seed weighing 3 grains lost i^-
grains of water when drying and entering the resting state.
This, I argued, would be the water that the resting seed would
take up when swelling for germination ; and it thus appeared
that in preparing for germination, a seed was merely resuming
its original unripe condition. But it was to the phenomena of
the shrinking process that my opportunities at first restricted
my attention during the early part of 1907 in Jamaica. Ob-
servations on the seeds of Ctesalpinia sepiaria, Canavalia ensl-
formis, C. gladiata^ and C. obtusifolia, led me to distinguish a
critical period in the shrinking process which roughly coincided
with the shrivelling of the cord or funicle, and the severing of
the biological connection.
When the soft, unripe, though full-sized seed was detached
before the cord began to shrivel, it lost 70 or 75 per cent, of
its weight in the drying and shrinking process ; but if the
detachment was effected after the cord had commenced to
wither, but before any drying of the seed was evident, then
the subsequent loss of weight was only about 50 per cent.
The result in the first case was a shrivelled seed ; in the second
case a normal resting seed. Now I assumed that the difference
between the two losses in the drying stage, viz. 20 or 25 per
cent., represented the water retained by the resting seed for
the support of the embryo, and I termed it "the water of
inclusion." In forming this inference I was also influenced by
the results of simultaneous observations on the seeds of other
plants, such as those of the Bastard Tamarind (Pithecolobium
filicifolium) ; but I need not here particularise them further.
My attention became then directed more especially to the
observation of the shrinkage of the soft, unripe, or uncontracted
seeds of two leguminous climbers, Entada scandens and
Mucuna urens, very favourable opportunities being afforded
THE HISTORY OF THE INVESTIGATION 5
at Moneague in the interior of Jamaica. In March 1907
I there studied the maturation of the seed on the living plant
and collected material which not only gave me employment
at the time, but has occupied me at various intervals ever
since. The results then obtained gave support to the theory
of shrinkage above noted, and when I returned to England in
May I adopted the water-of-inclusion theory.
I then set to work to procure the germination of seeds of
Entada, Mucuna, Canavalia, Abrus, etc., which had assumed
the typical resting state after being gathered in the moist, soft
condition, with their funicles beginning to shrivel ; and the
results confirmed the view suggested by the earlier observa-
tions that the resting seed in preparing for germination takes
up the water lost in the previous shrinking stage. In other
words, the swollen seed on the eve of germination resumed /
its condition of before the rest-period. The work was then
continued on these lines, guided more by opportunities than
by method. It was then argued that if the water absorbed for
germination is the water previously lost in the drying process,
it does not necessarily involve germination, meaning thereby
the commencing growth of the embryo. It was held that if
the above view was correct a swollen seed dried when on the
eve of germination ought to return to its original resting
weight and ought to retain its germinative powers. Both Therecipro-
these inferences were established by the results of several germination,
experiments discussed in the next chapter ; and I finally
adopted " the reciprocal theory," as it was termed, which is to
the effect that the water taken up for germination is the water
lost in the previous shrinkage process.
The theory of germination thus held good ; but it was
very different when one came to confirm by experiment the
water-of-inclusion view, which was really a theory concerned
with the embryo's life in the resting seed. It is there
suggested, as already pointed out, that some of the water The water of
which the shrivelled seed has lost through being prematurely se ed. es ms
detached is retained in the normally contracted resting seed
6 STUDIES IN SEEDS AND FRUITS
for the benefit of the embryo. From this point of view the
water-contents of seeds might be thus characterised :
A. The water lost in the normal shrinking process )
j j r r 5 P er cent -
and regained for germination . . . j
B. The water which the seed shrinking excessively )
loses and the seed shrinking normally retains j
C. The water which the normal resting seed loses 1
in the oven in addition to the water A and B j
Waterless residue . . . . . 15
100
Whilst A would be the water of germination, B would be the
water of inclusion or the water of the rest-period, and C would
be the water of combination, only to be driven off by exposure
to a temperature of 100 C.
It follows from the above view that all resting seeds
should possess impervious coats which would secure the
retention of the water of inclusion for the use of the embryo,
and that the result of puncturing the resting seed or baring it
of its coats would be a considerable loss of weight. It is also
implied that the abnormally shrunken seed would lose less
water in the oven than the normal resting seed.
To make a long story short, I may remark that all the
implications failed when put to the test. Many seeds proved
to have pervious coats. They, as a rule, preserved the same
weight when deprived of the protection of their coats by
baring or puncturing. Lastly, the abnormally shrunken seeds
lost about as much water in the oven as the normal resting
seed.
So my hypothesis, relating to a special supply of water for
the use of the embryo in the resting seed, collapsed. But
whilst putting it to the proof I had accumulated a large
number of results of experiments which are utilised in other
connections in the next chapter, and I chanced upon other
suggestive lines of inquiry. After determining the water-
percentage of seeds in the oven, I used to throw away the
sample. But on one occasion a sample of the broken-up
THE HISTORY OF THE INVESTIGATION 7
seeds of Guilandina bonducella was unintentionally left over-
night in the pan of the balance. Out of curiosity I noticed its
weight and found that it was 2 per cent, heavier than when
originally placed in the oven. In other words, a sample of
100 grains, which had been reduced in weight by exposure to A clue to a
a temperature of 100 C. to 92 grains, on the following morning
weighed 102 grains. This result was startling, and quite a
new road of investigation was opened up, occupying much of
my time for three years and supplying materials for several
of the chapters of this work. Under the stimulus of this
discovery I made at the time a few speculative comments in
my notebook, which proved to be the starting point of a theory
of cosmic adaptation to which Chapter XX is devoted. Here
again the seeds of Guilandina bonducella have been a source
of inspiration, and I soon got to realise that I owed much to
these interesting seeds.
But in the meanwhile my horizon had been greatly Thewiden-
extended. With the old theory gone it was evident that I ^or&l^of
could no longer treat the seed independently of the fruit, and the inquiry,
that I could no longer ignore the facts that the seed had
coverings, that the embryo in the resting seed was in all stages
of development, and that the reserve of food within the seed
presented great variations in amount as well as in disposition.
The investigation promised to branch out in a multitude of
ways, provokingly divergent in their direction. However, I
continued the method of following indications and was soon
hard at work again with the balance and the oven.
Since the seed-coats had played a variety of parts in the
experiments, one of the first of the new inquiries begun was
concerned with the seed-coat relation, meaning thereby its The seed-
relative weight as part of the entire seed. Great variety in coat relatlon -
this respect soon displayed itself. At the same time I began
to compare the seed-coat relation of the resting seed with that
of the soft, unripe seed and of the seed swollen for germina-
tion. Now commenced the separate treatment of the coats
and kernel in the oven experiments, when I was surprised to
8 STUDIES IN SEEDS AND FRUITS
find that the water-percentage for the coats was often greater
than for the kernel. Before long it was realised that materials
were gathering for a complete statement, as far as the indica-
tions of the balance and the oven went, of the part played by
On the way water in the economy of the seed from its immaturity through
lis rest-period to the germinating stage. I was in fact on my
way to the construction of the seed's regime in passing from
and swelling the unripe to the resting state and thence on to the germinating
seed. ,. .
condition.
Whilst engaged in this inquiry I took advantage of my
oven-experiments for the determination of the water-contents
of seeds to investigate further the curious fact that certain
seeds after being subjected in a broken condition to a
temperature of 100 C., being thus deprived of their free
water, not only regained all the lost water from the air, but in
a few days were markedly heavier than in the entire state.
This was found to be common with leguminous seeds
possessing impervious coverings. The unexpected results of
an experiment on the seeds of Entada scandens, which belong
to this type, threw fresh light on the matter. Separate
samples of the coats and kernel were subjected to the oven-
test, when the first experienced a loss of weight of about 15
per cent., and the second of about 10 per cent. They were
then left exposed for five days on a table, together with
samples of the coats and kernel which had not been heated.
It was then found that in all cases, whether with the heated
or unheated materials, the samples were considerably heavier
than before the experiment, the weight of the coats in both
cases being increased 2 or 3 per cent., and that of the kernels
3 to 5 per cent. There was, therefore, an inherent tendency
in both the coats and the kernel when separated from each
other to increase their weight by absorbing water from the air,
a tendency unimpaired by a previous loss of all the free water
through exposure to a temperature of 100 C. In other
words, the seed in the broken condition held more water than
in the entire state, and whether or not exposed to the heat-test,
THE HISTORY OF THE INVESTIGATION 9
the ultimate result was the same. Such was the commence-
ment of a long series of experiments which has extended off
and on over three years. In some of the early experiments I
tested the capacity for resorption possessed after heating by
leaves, wood, slices of fruits, etc., and also by hydrated
minerals, such as opal and chlorite.
Another line of inquiry first taken up at this time was
the determination of the relative weight of the embryo in other lines
albuminous seeds. An investigation somewhat crudely begun ln ^ mry -
soon branched off in many directions, the seeds of palms
figuring largely in the results. Almost at the commencement
of my work I had started experiments on the effect of time on
the weight of seeds. They were carefully weighed and placed
in paper packets, the intention being to extend the experiments
over years. At this time I was feeling my way in many small
inquiries, striking out blindly very often in my efforts to
obtain further clues. Thus I took with me to Jamaica in the
winter 1907-8 several seeds with the object of determining
their changes of weight under different climatic conditions, the
result being given in Chapter VII.
These investigations began in October 1906, and during
the first twelve months I mainly ignored the fruit ; but not
altogether, since during the summer I had been periodically The author's
observing some capsules of Scilla nutans to ascertain the no^directed
effect of cutting a window in the walls of the young fruit to the fruit,
on the maturation of the seeds. The experiment was not
deterrent and the changes not important. In a word, the
seeds of the Bluebell had behaved like those of a Gymno-
sperm. About the same time Lubimenko was carrying out
a similar series of experiments on leguminous pods.
Now began some observations on the dehiscence and
drying of the capsules of Iris Pseudacorus and of jEsculus
Hippocastanum (Horse-chestnut). I experimented with the
idea that dehiscence was the result of drying, a notion that
guided many subsequent experiments, though a year passed
before my error was discovered.
io STUDIES IN SEEDS AND FRUITS
The winter 1907-8 spent in Jamaica was chiefly occupied
in working as opportunity offered on the lines before indicated.
I repeated several of the experiments made in England on
the resorption of water from the air by seeds in the broken
My work in condition, so as to be assured that it was a capacity uncon-
Jamaica. ne cted with climatic causes. At this time I began my
observations on the Coco-nut (Cocos nucifera)^ ascertaining
the proportional weight of all the parts the husk, the shell,
the albumen, and the embryo and also determining their
water-contents.
The maturation and drying of the fruits of numerous
other plants also occupied my attention, such as those of
Anona^ Bauhinia, Citrus decumana (Shaddock), Datura, Entada,
Ipomcea^ Mahogany (Swietenia\ Sapota, etc. I was surprised
to find that the ripe capsule, the ripe legume, and the ripe
berry often lost much the same amount of water when
allowed to dry spontaneously, fleshy drupes like those of
Prunus (tested in England) behaving in the same fashion.
Then I reflected that fleshy fruits (drupes and berries)
corresponded to the full-grown living legume and capsule
in the moist, unopened condition, and that if we wish to
find the correlative of these dehiscent fruits in the dry,
opened state, we must look for it in the shrivelled currant
and the dried-up apple. This raised the whole question of
special adaptation in connection with seed dispersal. It was
argued that if we can discern no evidence of adaptation in
the shrivelled berry as regards seed distribution, we should
look for none in the drying capsule and pod, and that the
apparent display of method in the last-named is purely
accidental.
To enter more into the details of my work during my
second winter in Jamaica would be to anticipate much that
will be found in the succeeding chapters. I may, however,
say that one branch of inquiry which was more fully
developed was the hygroscopic behaviour of seeds, and
that my study of the maturation of the fruits of Momordica
THE HISTORY OF THE INVESTIGATION n
furnished me with some new ideas on the subject of the
sequence in the genesis of the berry and capsule, two types
of fruits often associated. With the observations on
Momordica my active work in Jamaica came to an end.
However, whilst spending the last few days on the summit
of Mount Diavolo, rambling in the forests and increasing
my seed materials for future work in England, the theory
of cosmic adaptation before alluded to was further elaborated.
During the spring and summer of 1908 I was occupied
in extending my observations on the rest-period of seeds, My work in
on the swelling antecedent to germination, on the relative ngan '
weight of the embryo in albuminous seeds, and on various
other subjects. In May I began a series of observations
on the fruiting and seeding of the Ivy (Hedera Helix\ which
have been extended to the spring of 1911. The result has
been to establish the growth of the embryo within the seed
throughout the winter months, and the not infrequent
germination on the plant (vivipary) in the spring. Here
much assistance has been received from collections of fruits
made at intervals during a winter by my sister, Mrs H.
Mortimer. In the late summer and early autumn my
systematic observations on the maturation, dehiscence, and
drying of fruits were resumed. The fruits included those
of Iris fcetidissima^ Quercus Robur (Oak), Arum maculatum^
Tamus communis^ and several other plants. In most cases
the inquiry was continued during the next two or three
years, the final result in the instance of the Oak being to
establish a slight but normal tendency to vivipary or germina-
tion on the tree.
Perhaps the most important outcome of these observations A clue to the
was the clue to the homology of fruits supplied by my observa-
tion of the shrinkage of seeds within the moist berry of
Berberis. This afforded a clue for the comparison of fruits
in their various stages, which was subsequently strengthened
by data supplied by the seeds of Arum^ Tamus, and Passiflora,
and ultimately enabled me to trace the homologies in the
12 STUDIES IN SEEDS AND FRUITS
ripening and drying stages of different types of fruits, such
as the legume, the capsule, and the berry, by fixing on a
stage common to all. The result was to further undermine
the prevailing notion of special adaptation to seed dispersal,
and to show that the mechanism of a dehiscing capsule or
legume, however adaptive it may appear, does not count for
more in nature than the shrivelling of a berry.
The winter 1908-9 was spent again in the West Indies,
A sojourn in mainly in Grenada and Tobago, but including a sojourn
Tobago*,' and f two or three weeks in Trinidad. It was at Port of Spain
Tnmdad. t h at j ma d e the acquaintance of Mr Hart, the late super-
tendent of the Botanic Gardens, and I was indebted to the
courtesy of Mr Evans, temporarily in charge, for the
opportunity of obtaining an abundant supply of ripe palm
fruits of different kinds. Mr Broadway of the Botanic
Station in Tobago kindly gave me valuable information
respecting Grenada, and subsequently assisted me by reply-
ing by letter to numerous queries I had put to him. To
Mr Anstead of the Botanic Station in Grenada I was very
deeply indebted for, so to speak, giving me the run of the
gardens and for other aid. The fruits and seeds of palms
occupied much of my attention in Grenada ; but I made
also several special studies, including one of the fruits of
Barringtonia speciosa (an introduced plant). It was in Tobago
that I made my first acquaintance with the " Twist Coco-nut,"
where the kernel lies loose within the hard shell.
But one of the most important lines taken up during
this winter was the study of the connection between monili-
form legumes and the abortion of ovules, which opened up
an interesting field of inquiry. The pods of Erythrina
corallodendron supplied me with my first clue. This raised
the question of the influence of the abortion of ovules and
of the failure of young seeds on the form, size, and weight
of the fruit ; and in this connection I made an extensive
series of observations on the pods of Albizzia Lebbek y Entada
polystachya, and Leuctena glauca. As often happened in other
THE HISTORY OF THE INVESTIGATION 13
cases, this led to another inquiry into the relation between
the number of seeds and the size and weight of the fruit,
which ultimately supplied me with materials for a special
chapter.
Whilst in Grenada I spent some weeks at the Grand Etang
in the mountainous interior of the island. My attention here
was occupied with many things in the surrounding forests ;
but I was particularly interested in studying the habit of
growth and the maturation of the fruit and seeds of Diocka
reflexa^ a leguminous climber, the seeds of which are amongst
those stranded by the Gulf Stream on the western shores of
Europe. The method of preparation of the seed for its
Trans-Atlantic voyage and the opportunities it possessed of
starting on its way were points of special interest for me.
To give an idea of my mode of work in the West Indies My work-
I will describe my work-room at St George's, Grenada. . . .
Hanging from nails on the walls to dry were the ripe fruits
of Cassia fistula^ Entada polystachya, and Hura crepitans (the
Sandbox tree). On the window sill exposed to the sun were
the opening fruits of Ravena/a madagascariensls^ displaying the
beautiful blue arils of the seeds and completing the process
of dehiscence which they had commenced on the tree. On
the sill of another window were the large square fruits of
Earrlngtonla speciosa in various stages of drying, all of which,
together with the fruits above mentioned, were methodically
weighed from time to time. On the table where I wrote were
placed at one end my balance and at the other end my copper
oven for the determination of the water-contents of seeds and
fruits. Close beside me lay a saucer containing the seeds of
Diocka reflexa from the green pod, which were silently illustrat-
ing the coloration process of leguminous seeds. In other
saucers around me lay a variety of seeds, all of them either
under observation or destined for future experiment, such as
the seeds of Barringtonia, Entada^ Enter oloblum^ Monstera, and
El<eis.
In a large press were two extensive series of pods of
In England,
1909-1910.
The Turks
Islands.
i 4 STUDIES IN SEEDS AND FRUITS
Albizxia Lebbek and Leuc<ena glauca^ arranged according to the
number of seeds, and from which I obtained my principal
material for investigating the relation between the number of
seeds and the size and weight of the fruit. In the same press
were two small paper trays containing the bared seeds of
C<esalpinia Sappan, Erythrina corallodendron^ and El<eis guineemis,
which, having been exposed to a temperature of 212 F. for
two hours, were now regaining from the air the moisture lost
in the oven. But perhaps the most interesting things around
me were a number of seeds of Earringtonia speciosa which had
been cut up with the hope of discovering the missing coty-
ledons. Lying about the room were many West Indian
fruits, such as those of Saccoglottis amazonica, Carapa guianensis^
and Mauritia settgera^ all from Trinidad ; whilst a box under
the table contained my collection of seed-drift from the
Trinidad and Tobago beaches, much of which had been
brought down by the Orinoco from the interior of the neigh-
bouring continent.
In the spring of 1909 I brought back to England abundant
material for further research in the various lines already
instituted. During the summer the observations on the
abortion of ovules and the failure of young seeds were con-
tinued, and I began to pay systematic attention to the
coloration of seeds, a subject about which many notes had
been previously made. At the same time I was arranging my
notes and working out the general results, during which many
" lacunae " presented themselves ; and it was with the filling
up of these gaps, together with the working up of results, that
most of the following twelve months were occupied. I may
add that large seed-collections were at my disposal for this
purpose.
At the close of 1910 I went to Turks Islands, which form
geographically the southernmost portion of the Bahamas, and
remained there three months. This locality was selected as
the most suitable one in the West Indies for the study of
oceanic seed-drift, or, in other words, for observing the dispersal
THE HISTORY OF THE INVESTIGATION 15
of seeds by currents, a subject which I had been following up
in various parts of the world since it first attracted my attention
amongst the coral islets of the Solomon Islands in the early
eighties, and one which I had constantly kept in view during
my previous three winters in the West Indies. I had made
collections in Jamaica, Tobago, and Trinidad, the large
quantities of Orinoco drift washed up on the southern beaches
of Trinidad proving full of interest. So I took up my abode
in Grand Turk, and from there visited all the cays of the
group, making a special study of the littoral plants and
especially investigating the abundant stranded seed-drift,
hardly any of which belongs to plants that have established
themselves in those islands, or in fact in the Bahamian region
generally.
Whilst at Grand Turk I was fortunate enough to meet
Dr Millspaugh, who was just completing the botanical survey The
of the Bahamian flora which Dr Britton, himself, and other su^eyofthe
botanists from the United States had been six years engaged Bahamas b y
_ ni i T i j iri i i i botanists of
in. The lurks Islands are the farthest south, and it might the United
Q, ,
have appeared as if I had come in to spoil the finish of a great *" u6S *
undertaking. However, our special interests lay far apart,
and I could not for a moment lay claim to a fraction of the
intimate knowledge possessed by Dr Millspaugh of the plants
of this region. I was the astonished spectator of the applica-
tion of his great experience to the flora of the little island of
Grand Turk. All the knowledge of years acquired through
the length and breadth of the Bahamas was brought to bear
within the narrow limits of the flora of this small island. It
was a lesson that I shall not readily forget. Dr Millspaugh
very kindly lent me the manuscript of the Flora of the
Bahamas by Dr Britton and himself ; and in return I gave
him a collection of seed-drift obtained from the beaches of the
group, which is now lodged in the Field Museum of Natural
History, Chicago. When the American botanists publish
their work they will enrich their science with the most complete
account of a flora hitherto made in the West Indian region.
o
1 6 STUDIES IN SEEDS AND FRUITS
This brings to an end my record of work and travel.
During the preparation of this book many other " lacunae," as
well as new lines of inquiry, have presented themselves. The
first I have been compelled to largely ignore, whilst the new
openings for investigation have been promptly blocked up.
But little has been said of my study of the rest-period of seeds
in this account of my work. As a matter of fact, however, it
has formed the pivot of my inquiries from the beginning to
the end. It started me on my work, and it is towards the
clearing up of the problem concerned in its mystery that many
lines of my inquiries now converge.
The work- Looking back at all the data collected in this investigation,
ing-up of my j am puzzled to account for their bulk. So often on returning
materials. r
home from my excursions it seemed that I had only made one
or two observations worth recording during the day. Yet
much of the work has been done by the seeds and fruits them-
selves, whilst I have stood by to register results. Whilst I
was engaged in weighing, or in some experiment, a score of
seeds and fruits were silently at work around me. Amongst
my seeds I have led a busy life, but no one has been so busy
as the seed itself. The labour came when all the results had
to be sifted, tabulated, and digested. The arrangement of the
materials indeed occupied a good deal of serious thought and
extended over a considerable time. It proved very difficult to
avoid two dangers : the first that of going over old ground ; the
second the assuming in an argument in an early part of the
work what could only be demonstrated in a later page. Ac-
cordingly I finally hit upon the method of first dealing with
the shrinking and swelling of seeds until the question of the
permeability or impermeability of their coats blocked the way
and demanded a response. This enabled me to open up the
whole matter of these qualities in seeds, and to establish a
nexus in the general arrangement of the work.
A serious And now for a serious word in concluding this chapter.
wor -The plan of sending forth treatises without a trace of the
personality of the worker is to me repellent. Knowledge in
THE HISTORY OF THE INVESTIGATION 17
itself has but few attractions for me. That knowledge which
brings one into touch with the life around one and enables the
observer and the observed to tell their common story is the
only thing that charms. I should feel no interest in inquiries
that led one to the confines of habitable space and left one
looking out on a dreary, cold, grey universe of nothingness. I
would instead get quickly home to my cosy terrestrial sur-
roundings and revel in thoughts that were comforting and
consoling.
Yet the fancy must always play a part if we wish to profit
by and to make a real advance in any investigation. It would
be easy to sustain the view that mere digging for facts is like
digging into the ground. Under such conditions one does
not see much beyond the length of one's nose. It is doubtful
whether the progress of knowledge thus effected resolves itself
into much more than the splitting up of phenomena, or into a
process of differentiation that can only end in a relative zero.
On the other hand, if at times we leave the solid ground of
fact and rise into the air on the wings of fancy, we can at all
events greatly extend our range of mental vision, and can
mark down points for investigation which never would have
come under our notice whilst adopting the mole's method of
inquiry. It is the man in the air that gives the directions, and
the man on the ground that does the work. By limiting our
field of inquiry and excluding the play of fancy we are groping
about as blindly as an army without its air-men. The dreamers
figure in my mind as the leaders of the world.
CHAPTER II
THE THREE CONDITIONS OF THE SEED
The three WE are all familiar with the three conditions presented by the
of theseed. ^ ar g e j so ^ t pre-resting seed, the contracted, hard resting seed,
and the soft, swollen seed on the eve of germination. Yet
to each of them we are apt to apply an epithet which is never
altogether true and rarely altogether wrong. Thus we often
speak of the pre-resting seed as immature, of the resting seed
as mature, and of the swelling seed as germinating. In these
connections it is necessary to remember that, as a rule, the
embryo is fully developed in the soft, swollen pre-resting
seed, and is quite ready, as shown in a later page, to proceed
with germination, should the shrinking process be averted.
If, then, the embryo is " mature " in the pre-resting seed,
such an epithet can have no distinctive value for the
resting seed.
So again, when we speak of the germinating seed, we have
to decide whether we mean the swollen seed on the eve of
germination, or whether we refer to the seed with the tip of
the radicle already protruding through the coats. Botanists,
like Nobbe, Pfeffer, Jost, and others, lay stress on the fact
that absorption of water by the resting seed is not actual
germination, but merely a preparation for that process ;
whilst gardeners are familiar with the circumstance that seeds
may swell up and not germinate. Strictly speaking, the
germinating condition with the radicular tip showing is a
fourth stage. It is a stage of growth and activity within the
18
seed, and cannot be compared with the three previous stages
(characterised by a passive vitality), which may be fitly
termed the shrinking, resting, and swelling stages. The
germinating stage may never be reached, since the absorption
of water that brings about the swelling of the resting seed is
more a mechanical than a vital process, and may or may not
terminate in the growth of the embryo, which is the essential
feature of germination.
The shrinking stage is characterised by loss of water, the The shrink-
swelling stage by absorption of water, and the intervening swelling
resting stage by a suspension, more or less complete, of the
drying process and by a greater or less state of passivity on the with water-
part of the embryo. It is with these three stages that we are water-gain.
now concerned, that of germination not coming within the
field of our inquiry. The shrinking of the pre-resting seed
and the swelling of the resting seed are the two processes to
be now discussed. It is the shrinking process that ushers in
the rest-period, and it is the swelling process that prepares the
seed for germination. In the first case there is water-loss, in
the second, water-gain ; and it may safely be assumed that as
a general rule we are here concerned mainly with these pro-
cesses, the proofs of which are discussed later on in this
chapter.
Here the balance becomes the instrument of investiga- Method of
tion ; and it is to the changes in weight in the different
processes that appeal is chiefly made. We deal at first
with the entire seed, the independent behaviour of seed-
coats and kernel being separately discussed in Chapter IX.
The weight of the resting seed is taken as one, whilst the
maximum weights of the pre-resting seed before shrinkage
begins and of the swollen seed on the eve of germination
are expressed in ratios. Thus, to take one of the very
largest of leguminous seeds, that of Entada scandens : a seed
which weighed 1004 grains in the soft, swollen condition
weighed 408 grains in the contracted resting state ; and sub-
sequently, when on the eve of germination, it increased
20 STUDIES IN SEEDS AND FRUITS
its weight to 1012 grains by water-absorption. We thus
get the result :
Large, soft, pre- Restine seed Swollen seed on eve
resting seed. of germination.
1004 grains. 408 grains. 1012 grains,
which expressed in ratios becomes :
Shrinking ratio. Resting seed. Swelling ratio.
2-46 I 2-48
Modes of The ideal method of carrying out such observations would
fhe^hrinking naturally be, as was done in the instance just given, to note
and swelling the shrinkage and swelling of a single seed, that is, to take its
maximum weight in the green fruit, to weigh it again after
prolonged air-drying, and to weigh it once more when on the
eve of germination. This involves the separation of the pre-
resting seed from the parent plant ; and although one can
choose the time when the cord or funicle is beginning to
shrivel and the vital connections are being severed, still it is
open to the objection that a seed thus detached does not dry
under normal conditions. However, checks can often be
found by comparing the state of the coats of a resting seed
thus produced with that of a typical resting seed ; whilst any
marked divergence from the average can be detected by a
comparison of the swelling ratios of the two seeds. With
seeds typically impermeable, a resting seed thus artificially
obtained often lacks the impermeability of the outer coverings ;
and its shrinkage, as indicated by the change in weight, is not
so great as with the seed that has properly contracted on the
plant.
On the other hand, typical permeable seeds when dried
under these conditions frequently shrink too much. Never-
theless, normal results were at times obtained, some of which
are mentioned below ; whilst the behaviour of the imperfectly
shrunken seeds has offered a fruitful field of investigation.
But there is another plan, and that is by comparing the
average shrinkage of a number of detached pre-resting seeds
with the average swelling of a number of resting seeds prepar-
THE THREE CONDITIONS OF THE SEED 21
ing for germination. This method is more practicable and has
been frequently employed, and, although open to the same
objection as regards the premature separation of the seeds from
the parent plant, it is easy, by the use of normal seeds as a
check, to exclude those where the shrinkage has been irregular.
A third method employed at times, especially for the
shrinkage, has been to compare the average weight of a
number of full-sized pre-resting seeds or of seeds swollen for
germination with the average weight of a resting seed. This
is exposed to the objection that seeds vary much in weight, an
objection losing some of its force if a large number of seeds
are used.
With reference to the determination of the maximum
weight of the swelling seed, it would appear difficult to
ascertain where simple absorption ends and germination, or
active growth within the seed, begins. In practice, however,
this difficulty does not often arise, and it can usually be met
by frequently weighing the swelling seed up to the beginning
of germination, an approximate estimate being alone expected.
By way of opening the subject I will first deal with my observations
experiments on single seeds or sets of seeds, where the history shrinking
has been followed for each seed from its soft, swollen pre- and swelling
, , . . , . ratios of
resting condition through the rest-period on to the swelling single seeds
T i . or sets of
stage terminating in germination, i possess such a continuous seeds in( ji.
series of observations for the seeds of four leguminous and one cate that the
, . ... water lost in
malvaceous species. As given m the tables subjoined, these shrinking is
data afford an early indication of a principle which will figure swelling for
prominently in subsequent pages, that the water lost in shrink- S ermmatlon -
ing is regained in swelling for germination. Thus, if a full-
sized pre-resting seed weighing 100 grains shrinks to 40 grains
during its drying, and after a rest-period of some months
regains its original weight of 100 grains when swelling for
germination, we have data directly indicating such a principle.
There is much in these tables that will be elucidated as the
work proceeds ; but I may here point out that the behaviour
of the imperfectly shrunken seeds of Guilandina bonducella there
22 STUDIES IN SEEDS AND FRUITS
noted lends a double support to this view, since it indicates
that if less than the normal amount of water is lost in the
shrinking process, less is also required in swelling for germina-
tion. In Table A the histories of single seeds, and in Table
B the history of a group of seeds, are followed in all three
stages, the pre-resting, the resting, and the swollen stage
preparatory for germination.
A. SHOWING THE WEIGHTS OF THE SAME SEED IN ITS UNRIPE OR
PRE-RESTING CONDITION, IN ITS RESTING STAGE, AND ON THE EVE
OF GERMINATION.
Name of plant.
Weight in grains.
Shrinking and swell-
ing ratios.
Duration of the
resting stage.
Entada scandens A
:: - I
Dioclea reflexa
Poinciana regia
Unripe. Resting. Swollen.
969 371 930
1004 408 1012
954 380 985
239 in 212
24-3 ID'S 25-3
Shr. Rest. Sw.
2'6z 2*51
2*46 2*48
2-51 2-59
2-15 1-91
2-31 2-41
3 months.
4
3^
a*
4i ..
B. SHOWING THE TOTAL WEIGHTS OF A NUMBER OF SEEDS OF
THE SAME SPECIES IN THE SAME THREE STAGES.
Guilandina bonducella (4
seeds).
Thespesia populnea ( 1 1
seeds).
416*0 i76'o 449*0
607 34-9 62-7
2-37 I 2-55
(3-20 I 3-08)
1 74 i i '80
4^ months.
4
The same
reciprocal
relation be-
tween the
shrinking
and swelling
processes is
established
by independ-
ent observa-
tions on a
number of
seeds.
Note. All the seeds in these experiments germinated. Those of Guilandina bonducella
did not complete the shrinking process, becoming permeable but "germinable" seeds.
The ratios obtained independently for the normal impermeable seeds are in this case
given in brackets.
The general indications afforded by observing individual
seeds from the pre-resting stage to germination are confirmed
and extended by the large amount of additional data given in
the two tables subjoined. In Table A are arranged all my
results on the shrinking and swelling ratios of seeds belong-
ing to about ninety-six species, of which all but those in the
supplementary list of palm seeds, etc., belong to the present
discussion. They have for the most part been obtained
THE THREE CONDITIONS OF THE SEED 23
independently from different seeds or sets of seeds of the
same species, since the opportunities of making a successful
series of observations on individual seeds were rare. In
Table B will be found a number of swelling ratios for other
seeds as determined by the data supplied by Hoffmann and
Nobbe. As supplementing my own results they are extremely
valuable, since they supply some of the conspicuous deficiencies
in Table A, and enable one to extend the field of inquiry in
a tentative fashion over a large portion of the seed-bearing
plant-world. It should of course be remembered that even
with the best of observers and the best of conditions such
results can only be approximations ; and it must not be
forgotten that we are concerned here not merely with one
process, but with all those changes concerned with the transition
from the pre-resting stage to the eve of the germinating
condition. The results as a whole are to be regarded here
as supporting the general contention, based on the study of
individual seeds, that the seed in swelling for germination is
as a rule returning to the pre-resting or so-called unripe
condition, that it gains in swelling what it lost in shrinking,
and that the relation of the swelling to the shrinking seed is
mainly reciprocal, the resting stage figuring as an interruption
in the embryo's development in response to the pressure of
external conditions.
Before discussing these data, one may remark that there
is little that is novel in the enunciation of this principle.
Gardeners must often act on the tacit assumption of its reality,
and scientific investigators have gone far to establish it. In
O o
our case it is particularly necessary to possess a clear conception
of the mutual relation of the shrinking and swelling processes,
since without the establishment of some preliminary general
principle we should be unable to study with profit the
mechanism of these processes as exhibited in the separate
behaviour of the seed's coats and its kernel (see Chapter IX).
This principle was so fully expected and accepted by Dr Dr Nobbe's
Nobbe that he was satisfied with only a few experiments proof>
24 STUDIES IN SEEDS AND FRUITS
for its demonstration. In his Handbuch der Samenkunde,
published in 1876, he shows that in the case of the seeds of
the Common Bean (Faba vulgaris} the water lost in the shrink-
ing process was gained back in the swelling stage. In the act
of swelling, he says, the original volume of the " fresh " (or
pre-resting) seed is restored (p. 71). Two of these fresh seeds
were allowed to go through the shrinking process, the minimum
size being reached in about ten days. Measurements were
taken ; and it was ultimately found that one of the shrunken
seeds when placed in water regained its original dimensions in
about four days, whilst the other kept in a chamber saturated
with water-vapour regained but little of its original size after
five weeks.
TABLE A. SHRINKING AND SWELLING RATIOS OF SEEDS (GUPPY).
Note, The ratios represent the relation in weight between the resting seed and the
pre-resting and swelling seeds, the resting seed being taken as i. Thus if a seed weighed
25 grains before shrinking, 10 grains when resting, and 24 grains when swollen for
germination, its formula would be 2*5 i 2*4, the shrinking ratio being indicated on
the left, and the swelling ratio on the right.
Average
weight
Permeable,
Family.
OI 3.
resting
Ratios.
impermeable,
or variable.
seed in
grains.
Abrus precatorius .
Leguminosae
'S
Shr. Sw.
2-15 2-25
Variable.
Acacia Farnesiana .
>)
2'0
2'13 2'00
j |
Adenanthera pavonina
ii
47
2-42
Impermeable.
^Esculus Hippocastanum
(Horse-chestnut) .
Hippocastaneae
130-0
2-17
Permeable.
Albizzia Lebbek
Leguminosae
2 '3
2-27
Variable.
Allium ursinum
Liliaceae
O'l
2 '00
Permeable.
Andira inermis
Leguminosae
25-0
2 '09
Anona muricata
Anonaceae
6-0
I -40 I "43
,, palustris
99
4-0
*"45
9 9
Aquilegia (species) .
Arenaria peploides .
Ranunculaceae
Caryophyllaceae
o'O3
0-25
1-62
I'8 S
Variable.
Artocarpus incisa (Bread
fruit) .
Artocarpeae
45'
2 '22
Permeable.
Arum maculatum
Aroideae
'5
I-6 3
9 9
Barringtonia speciosa
Myrtaceae
380^0
278
99
Bauhinia sp. . .
Leguminosae
4-0
2'10 2'2O
Variable.
Berberis sp.
Berberideae
0'12
I'92
Permeable.
Bignonia sp. .
Bignoniaceae
5'
2'30
99
THE THREE CONDITIONS OF THE SEED 25
TABLE A. continued.
Average
weight
Permeable,
Family.
01 a
resting
seed in
Ratios.
impermeable,
or variable.
grains.
Caesalpinia sepiaria .
Leguminosae
4'S
Shr. Sw.
2 '25 2 '20
Variable.
,, Sappan .
I0'0
2'10 2'24
Cajanus indicus
3-0
2'4O 2'IO
Permeable.
Calliandra Saman .
4-0
2-50
Variable.
Canavalia ensiformis .\
24*0
2*30 2*00
Permeable.
,, gladiata .
47 -o
2 '60 2'OO
Variable.
, , obtusifolia
I2'0
2*44 2*54
,9
,, sp. . ...
i8'o
i "94
9 9
Canna indica .
Cannaceae
2 7
i '47 1*50
9 ,
Cardiospermum grandi-
florum .
Sapindacere
3-0
170
Permeable.
Cassia fistula .
Leguminosae
4-0
276 2*52
Variable.
,, grandis
,,
9-0
I'll
99
,, marginata
,,
IO'O
2'10
J(
Chrysophyllum Cainito .
Sapotaceae
I2'0
i '45
Permeable.
Citrus decumana (Shad-
dock) ....
Aurantiaceae
4'5
i '65 i '60
99
Crinum sp. .
Liliaceae
50*0
2*35
9 9
Datura Stramonium
Solanaceae
0*14
1-50
Dioclea reflexa
Leguminosae
90*0
i '90 i '80
Impermeable.
i) i)
ti
lOO'O
2 '2O 2IO
Permeable.
Entada polystachya .
,,
6-6
2'22 2'29
t)
,, ,,
,,
S'
2-S2
Impermeable.
,, scandens
11
400 'o
2-5I 2'47
99
Enterolobium cyclocarpum
,,
17-0
Variable.
Erythrina corallodendron
3' 2
2'l6
99
,, indica
,,
13-0
2'49
,, velutina .
,,
7'5
2*40
Faba vulgaris(Broad Bean)
,,
33 '<>
2-30 I'95
Permeable.
Gossypium hirsutum
Malvaceae
1*0
I -80
t)
Guilandina bonduc .
Leguminosae
50 'o
2'47
Impermeable.
, , bonducella
,,
40*0
3'2o 3 '08
,,
,, melanosperma
,,
42 - o
2 '43
99
,, (species of) .
,,
6o'o
2-52
99
Hedera Helix .
Araliaceae
0-4
2'OO 2'12
Permeable.
Hibiscus elatus
Malvaceae
'S
2'OO
,,
,, esculentus .
,,
0-8
170
,,
,, Sabdarifa .
,,
0-4
I '90
99
Hura crepitans . .
Euphorbiaceee
20 '0
2'29 2'10
99
Ipomrea pes-caprae .
Convolvulaceae
3'0
3'20 2'45
Impermeable.
,, tuba .
ii
5*0
3*30 2*60
99
,, tuberosa .
ii
25-0
2-40 2-45
Variable.
Iris foetidissima
Irideaj
075
3-40
Permeable.
,, Pseudacorus .
,,
072
2' 50 2'OO
M
Leucsena glauca
Leguminosae
0-8
2*84 2 '62
Impermeable.
Lonicera Periclymenum
(Honeysuckle)
Caprifoliaceae
0*07
172
Permeable.
Luffa acutangula
Cucurbitaceae
I'O
177
99
Momordica Charantia
ii
3-0
I'SO
26 STUDIES IN SEEDS AND FRUITS
TABLE A. continued.
Average
weight
Permeable,
Family.
ot a
restinc
Ratios.
impermeable,
or variable.
seed in
grains.
Monstera pertusa
Aroideae
0-8
Shr. Sw.
2-44 i
Permeable.
Montrichardia arborescens
35 -o
2*40 i
!>
Mucuna urens .
Leguminosae
90 - o
i '80 i 2*05
Impermeable.
Opuntia Tuna .
Cacteae
I'O
1*90 i
Permeable.
Phaseolus multiflorus
(Scarlet-runner) .
Leguminosae
i8'o
2*50 i 1*98
)(
Phaseolus vulgaris (French
Bean) ....
I2'0
i 1*84
>
* Pisum sativum (Pea)
,,
6-0
2*80 i 1*91
Pithecolobium filicifolium
n
13-0
1-58 I
,,
Poinciana regia
,,
IO'O
2-31 I 2-37
Variable.
Primula veris (Primrose) .
Primulaceae
0'012
2-36 I
Permeable.
Pyrus Malus (Apple)
Rosaceae
o'4o
1*90 I
,,
Quercus Robur (Oak)
Cupuliferas
25-0
2^50 i
ii
Ravenala madagascariensis
Musaceae
S'
I '60 I
Ribes grossularia (Goose-
berry) ....
Ribesiaceae
0*09
I '63 I
ti
Ricinus communis (Castor
Oil) . . .
Euphorbiaceae
3 '5
I 1-33
,,
Scilla nutans .
Liliaceae
O'l
i "60 i
Stellaiia Holostea .
Caryophyllaceae
0-45
I'82 I 2'10
)>
Swietenia Mahogani
Meliaceae
37
3-78 I
>
Tamarindus indica .
Leguminosae
20 'o
I 2-15
ii
Tamus communis
Dioscorideae
0-25
175 I
M
Theobroma Cacao (Cocoa)
Buttneriaceae
20 'o
1-37 I
,,
Thespesia populnea .
Malvaceae
3'
1-87 I 1-82
Variable.
Ulex europaeus
Leguminosae
O'll
2*30 I
Impermeable.
Vicia sativa
it
0-31
2*26 I
Permeable.
,, sepium .
o'3S
I '90 I
Variable.
Vigna luteola .
0*70
2-45 I 2-7
Impermeable.
SUPPLEMENTARY LIST (see Note 20 of Appendix).
Prunus communis (Sloe) .
Rosaceae
I "00
89 /
The question
Acrocomia lasiospatha
Palmaceae
30*0
'47
of perme-
Areca Catechu
,,
40 'o
72
ability does
Cocos nucifera (Coco-nut)
,,
4600 'o
89
not here
,, plumosa
,,
6-0
'59
arise. In
Hyophorbe Verschafftii .
,,
5'
'IS
all cases the
Mauritia setigera
,,
300-0
75
seed proper
Oreodoxa regia
,,
5'
' 2 3
is here re-
Sparganium ramosum
Pandanaceae
o'o6
2 '00
ferred to.
* See Note i of Appendix. The seeds were abnormally shrivelled. As with Faba
vulgaris (Broad Bean) and Phaseolus multiflorus (Scarlet-runner), the seeds of Pisum
sativum (Pea) shrink excessively if detached from the pod. It is therefore not possible
to get good results in these cases.
THE THREE CONDITIONS OF THE SEED 27
TABLE B. SWELLING RATIOS OF SEEDS (HOFFMANN AND NOBBE).
Swelling ratios of seeds adapted from the results obtained by Hoffmann and Nobbe,
and given in the latter's Handbuch der Samenkunde, p. 119, etc. (The weight of the
resting seed is here taken as i , as in the previous table. )
Hoff-
mann.
Nobbe.
Page refer-
ences, etc.
Triticum vulgare (Wheat)
Gramineae
'455
1*600
p. 119.
Hordeum vulgare (Barley)
482
...
Secale cereale (Rye)
'577
lt
Avena saliva (Oats) .
598
()
Zea Mays (Maize) . . y
440
1*398
Panicum miliaceum (Millet)
250
t
Fagopyrum esculentum (Buck
Polygonaceae
'460
Ervum lens (Lentils)
Leguminosae
t v v
'934
j}
Pisum sativum (Peas)
2*068
/(a) 1*960)
pp. II 9 , 122.
Phaseolus sp. \
(Weisse Bohnen, White Beans) /
,,
i '921
...
P. multiflorus?
Phaseolus vulgaris .
1 (a) 2*175 I
pp. 119, 123,
124.
Faba vulgaris (Broad Beans)
2*040
2*570
pp. 109, 119.
Vicia, Lathyrus (Velches)
'754
p. 119.
Medicago sp. sp. (Lucern)
1*560
'i'*8 7 8
p. 120.
Trifolium repens (White Clover)
2*267
i "890
n
,, pratense (Red Clover)
2*175
2*053
I)
Papaver sp. sp. (Mohn, Poppy)
Papaveraceoe
1*910
P. somniferum,
etc.
Brassica Napus varieties (Raps)
Cruciferas
1*510
1*483
pp. 80, 96, 1 20,
418,431.
Raphanus sativus chinensis (Oel-
rettig)
,,
1*080
i '595
pp. 36, I2O.
Camelina sp. sp. (Leindotter,
Cameline)
,,
1*600
pp. 120, 359.
Cannabis saliva (Hemp) .
Cannabineae
i '439
pp. 90, 1 2O.
Helianthus annuus (Sunflower)
Compositae
1*565
pp. 120, 518.
(Weisse Rube) .
1*625
1*518
p. 120.
(Zuckerriibe) .
2*205
,,
Pinus austriaca
Coniferae
7*358
!
Note. According to Siewert, quoted on p. 120, the Lupines (Lupimts) have a
swelling ratio of 2*00 to 2*30.
With regard to Table B, it is to be observed that the
original swelling results were stated as percentages of the
weight of the resting seed. These have been converted into
the ratios employed for my own results in Table A, where the
shrinking and swelling processes are combined in one simple
formula, the resting seed being taken as i. To have treated
28 STUDIES IN SEEDS AND FRUITS
the swelling process as a thing apart would have been to
ignore its all-important reciprocal relation to the shrinking
process. This conversion is easy. Thus, whilst Nobbe states
the swelling capacity of Wheat at 60 per cent., and Hoffmann
puts that of Broad Bean (Faba vulgaris) at 104 per cent., I
should state them as 1-60 and 2-04 respectively, the resting
seed being I-QO.
Value of the Although there is a distinction to be drawn, as will be
Tables A subsequently pointed out, between the water required for
and B. germination and the water necessary to saturate a seed, seeds
under ordinary swelling experiments are apt to strike a rough
average of their own by germinating, so that such experiments
frequently prove to be germination experiments, in which one
has to fix a somewhat arbitrary limit indicating where swelling
ends and germination begins. This was in fact an almost
invariable rule in my own experiments ; but by placing the
seed in its earliest swelling stage in damp moss, excessive
estimates were probably avoided. I do not gather that either
Hoffmann or Nobbe attached much weight to the distinction
between the swelling needed for germination and the swelling
involved in saturation. Indeed, the latter expressly states
(pp. 119, 1 20) that the kernels require as a rule to be
thoroughly soaked before germination begins. In his care-
fully guarded recorded experiments the seeds were either
immersed in water or kept moist by pouring water over them,
methods that seem likely to produce excessive estimates. Yet,
except in the case of Faba vu/garis, his results as a rule come
near to those obtained by Hoffmann for the same species ; and
in spite of the difference in our methods my estimates for
Pisum sativum (Pea), Phaseolus vulgaris (French Bean), and
Phaseolus multiflorus (Scarlet-runner), are not far separated from
those of Nobbe. This will be seen in the comparison made
in Note I of the Appendix. As I have said before, the seeds
assert themselves in ordinary experiments, and, disregarding
divergent conditions, strike out a rough average result for all.
For these reasons, therefore, we may, I think, claim that the
THE THREE CONDITIONS OF THE SEED 29
results given in Tables A and B for the swelling ratios are
fairly representative of the relative values of the swelling
processes which precede germination in a state of nature.
It will have been inferred that if the seed in swelling for In the recip-
germination takes up the water lost in shrinking, the processes acterofthe
must be essentially mechanical in their nature. That the
swelling of a seed is essentially a mechanical process was processes is
i i- 7 i i T-V XT i i r T.1 involved their
established by Dr Nobbe in a variety or experiments. Thus, essentially
he found that Clover seeds swelled with much the same
readiness in ordinary pure water as in water that had been
previously either oxygenated, or carbonated, or chlorinated
(pp. 1 02, 103) ; whilst he showed that the absorbing capacity
is largely independent of the retention of the germinating
powers, since seeds of Lady's-fmgers (Anthyllis vulneraria\ with
a low germinative value (8 per cent.), swelled almost as freely
as seeds of which nearly all (86 per cent.) were able to ger-
minate (p. 1 14). The swelling of a seed, as he asserts
on p. 101, is merely a mechanical process preparatory for
germination.
In the course of my own observations with the balance,
there presented themselves a number of other proofs of the
mechanical and reciprocal character of the shrinking and
swelling processes. These are merely summarised or illustrated
in the remarks immediately following, references being there
made to where a detailed treatment of the points raised will
be found.
That the increase in weight of a seed in preparing for Additional
germination is essentially due to absorption of water is mechanical 6
indicated: nature of the
swelling
(1) By the fact that when a seed on the eve of germination process.
is dried in air at the ordinary temperature it returns
approximately to its original weight as a resting
seed ;
(2) By the circumstance that the weight-relations between
the kernel and its coats and between the embryo (in
albuminous seeds) and the other parts of the seed
First, that a
seed on the
eve of ger-
mination
returns ap-
proximately
to its original
weight.
3 o STUDIES IN SEEDS AND FRUITS
are much the same in the seed that has been dried
after swelling for germination as they are in the
resting seed ;
(3) In the fitness of the embryo in many pre-resting seeds
to pass on at once to germination without the
intervention of the resting stage.
The results of a number of experiments on leguminous
seeds indicate that when a seed on the eve of germination is
dried under ordinary air conditions it returns approximately to
its original weight. In illustration there are given below five
examples selected from the table in Note 2A of the Appendix,
where numerous other results, all pointing to the same
conclusion, will be found, together with a discussion of the
general nature of such experiments. All the results refer to
seeds that subsequently germinated.
EXAMPLES OF THE EFFECT OF DRYING UNDER ORDINARY AIR CONDI-
TIONS ON LEGUMINOUS SEEDS THAT ARE READY TO GERMINATE
(taken from Note 2 of the Appendix).
Weight in grains.
Permeable
Gain ( + )
or
Swollen
or
impermeable.
Resting
for
After
loss ( - )
seed.
germi-
drying.
nation.
Guilandina bonducella .
Impermeable
33'35
97'3
35'35
+ 6 'o per cent.
Entada scandens .
312-50
728-00
318-70
+ 2-0
Poinciana regia .
Variable
870
19-50
8-70
'
Phaseolus vulgaris
(French Bean) .
Permeable
n's
24 '60
13*35
- i'i ,,
Faba vulgaris (Broad
Bean) . . .
>
41 50
86-30
40*60
-2'Z
Note. A plant with both permeable and impermeable seeds is characterised as
' ' variable. "
Although these samples support the view of the mechanical
nature of the swelling process, they present curious divergencies
in their behaviour when dried ; and the same may be said
of the other results incorporated in the table in Note 2A. It
appears, therefore, that as compared with their weight in the
THE THREE CONDITIONS OF THE SEED 31
resting state some seeds on being dried in air after reaching
the point of germination are heavier, others are lighter, and
others remain unchanged. Various disturbing causes that
would be likely to come into play in the course of the experi-
ment here suggest themselves ; but they can usually be
eliminated ; and, as shown in Note 2 A, none can account
for the great contrast in the behaviour of the seeds of
Guilandina bonducella and Faba vulgaris, where in the one
case there is a gain of about 6 per cent., and in the other a
loss of 2 per cent.
However, as will be seen in the table, as well as in the
illustrations given above, these marked differences are displayed
by two distinct types of seeds, the impermeable as represented
by Guilandina bonducella^ and the permeable as exemplified by
Faba vulgaris. A good deal of this contrast, therefore, lies
behind the distinction between permeable and impermeable
seeds ; and its significance will become evident only after a
detailed consideration of those two types of seeds.
The second additional proof that the swelling of a seed for Second, that
germination is essentially concerned with absorption of water relation! of
might seem to be included in the first ; but there we were c ats, kernel,
albumen, and
concerned with the seed in its entirety, whilst here we are embryo are
dealing with its parts. The proof lies in showing that the same in the
absolute weight of parts that obtains in the resting seed is in !fte r swell-
the main preserved in the seed that has been dried after swelling in r for & er -
r r- MI i-ji_i minationas
tor germination, .bour illustrations supplied by leguminous they are in
seeds are here given ; but for full details on this subject se ed reS
reference must be made to Note 3 of the Appendix. I am
here giving the results of observations on single seeds, and
these are compared with the average weights of the parts in
resting seeds of about the same size. The parts of the swollen
seed were separated in the wet state and allowed to dry in an
ordinary room. The small changes in weight that actually
occur have a significance which is alluded to in a later page ;
but they are not such as to materially affect, the general
conclusion to be drawn from the comparisons. The first two
32 STUDIES IN SEEDS AND FRUITS
seeds are exalbuminous, and here one is concerned only with
the coats and the kernel. The last two are albuminous, and
we have, therefore, in their cases to distinguish between the
albumen and the embryo.
COMPARISON OF THE WEIGHTS OF THE COATS, KERNEL, AND EMBRYO
(IN TWO CASES) IN RESTING LEGUMINOUS SEEDS, AND IN THE SAME
SEEDS WHEN DRIED AFTER SWELLING FOR GERMINATION.
Resting seed
average.
Swollen
seed.
Dried
swollen seed.
Mucuna urens (exalbu- / coats
minous) . . . \ kernel
237 grains
6 4'4 ,,
34 -2 grains
136*1
23 'i grains
66-9
88-1
i7'3
9'
Faba vulgaris, Broad / coats
Bean (exalbuminous) \kernel
5-6
34'4 ,,
40-0 ,,
II-2
68-8
5'7
33'3 >,
8o'o ,,
39'
Poinciana regia (albu- f^men
minous) . . -\ embryo
4'95 >.
2'35 ,.
27 ,
9'43 ,
7-36
6-21
4'6o ,,
2-90 ,,
2'5 >.
lO'OO ,,
23*00 ,,
lO'OO ,,
c ouT gi " at ^ (alb "1^ Smen
^ embryo
^84 ,,
5^9 n
l'*7 .
5 '9 >i
1270 ,,
2-80 ,,
270
5-65
i'23
9-80
21-40
9-58
Third, that
the embryo
in many pre-
resting seeds
is able to
pass on at
once to ger-
mination.
Nature often supplies evidence of the readiness of seeds to
"jump " the rest-period, the shrinking and swelling processes
being then dispensed with. This is what we would expect if
the shrinking of the soft pre-resting seed and the swelling of
the hardened resting seed are essentially concerned with the
loss and absorption of water. But in thus appealing to the
potential vivipary of seeds we do so only in a very general
sense, since numerous other influences may come into play.
Though typically the resting stage represents a complete
interruption in the embryo's development, this is not always
so. A treatment of this complicated subject will be found
in a later chapter ; and it is there shown that in the case of
THE THREE CONDITIONS OF THE SEED 33
the seeds of plants like Arenana peploides, Vitia septum. Iris
PseudacortiSy etc., which under normal circumstances enter into
the typical resting state, it is possible, by keeping the soft,
uncontracted pre-resting seed in warm, moist conditions, to
induce germination, thus dispensing altogether with the
shrinking and resting stages.
Before making further reference to the ratios for the Neither the
shrinking and swelling of seeds, it should be pointed out
that as a rule neither the full-grown, uncontracted pre-resting
seeds nor the resting seeds swollen and ready for germination for germina-
f . T i i 11 i tionarein
are in a state or saturation. Both markedly increase their a state of
weight when placed in water. The distinction between the saturatlon -
amount of water required for germination and the larger
amount needed for saturation is dealt with in a later page
of this chapter. Here I will more particularly allude to
the behaviour of the soft pre-resting seed in this respect.
According to the principle that the swelling seed gains what
the shrinking seed loses, we should infer that the behaviour
of the large pre-resting seed and of the swollen seed on the
eve of germination would be the same. This proves to be
the case.
When in Jamaica, I found that full-sized soft seeds from
the moist green pods of Guilandina bonducella gained about
20 per cent, in weight when placed in water ; whilst, in the
failures of my germination experiments, when the seeds were
kept in wet moss, the weight of the swollen seed was often
correspondingly in excess of the normal weight for germination.
So in England with seeds of Fab a vu/garis (Broad Bean) and
Phaseolus multiflorus (Scarlet-runner), I obtained similar results.
Here, full-grown soft seeds from the green pod, that is to say,
seeds that had not yet begun to shrink, added at least 10 per
cent, to their weight after lying in water for half a day. Then,
again, resting seeds of Faba vulgaris, that under ordinary con-
ditions would have germinated when their weight had increased
by 90 or 100 per cent., did not germinate at all when allowed
to remain in water, but kept adding to their weight by
3
34 STUDIES IN SEEDS AND FRUITS
absorbing more water, until they had reached their saturation
point of about 120 per cent.
A closer con- We are now in a position to consider more closely the
thSrinking shrinking and swelling ratios before tabulated. There are
and swelling dealt with in these tables the results of observations on the
seeds of more than 100 plants, four-fifths of which, as given
in Table A, are from my own observations, whilst the rest, as
included in Table B, are from the observations of Hoffmann
and Nobbe. They belong to 38 families and comprise about
80 genera, of which rather over one-third are leguminous.
In three or four cases only, viz. Pisum sativum, Faba vu/garis,
Phaseolus vulgaris^ and perhaps P. multiflorus^ are the same plants
referred to in both tables.
In the list containing my own results, seeds alone are dealt
with, seed-like indehiscent fruits being excluded ; but in Table
B we find also the " grains " of Cereals and a few seed-like
indehiscent fruits, such as those of Buckwheat ; but 1 do not
apprehend that the swelling ratios will be very materially
affected. Dr Nobbe himself did not regard this disturbing
cause as concerning the validity of his comparison (p. 112);
and from my own observations on fruits to be subsequently
discussed 1 would infer that, at all events with the grains of
Cereals, which comprise most of the seed-like fruits in Table
B, the effect of the coverings would be rather to lessen than
to increase the contrast which evidently exists between the
swelling capacities of the seeds of Cereals and the seeds of
other plants.
The views of Dr Nobbe sums up very briefly the results obtained by
Hoffmann and himself concerning the swelling capacities of
seeds (p. 120). Leguminous seeds, he infers, possess the
highest capacity for absorbing water, whilst the lowest is
possessed by oily and resinous seeds and by the grains of
Cereals. This inference receives a general support from the
results in Table A, and it will be sufficient at present to take
the two extreme cases in illustration, the seeds of Ricinus
communis absorbing one-third of their weight of water before
THE THREE CONDITIONS OF THE SEED 35
germination, whilst those of the leguminous Guilandina
bonducella treble their weight. But this cannot take us very-
far. A host of questions present themselves as we run
our eyes down the lists ; and when we endeavour to answer
them off-hand, a long vista of undetermined influences
opens up. It would be easy to discover differences and
to formulate distinctions ; but they would have little or no
meaning now ; and it would be futile at present to base
any general contrast, such as between families or between
genera, on these data. (As already remarked, indehiscent
fruits of the type found in palms and in genera like
Prunus and Sparganium do not come within the limits
of this discussion, but are referred to in Note 20 of the
Appendix.)
We have yet to appreciate the value and to estimate the The diffi-
significance of such distinctions. Behind the varying behaviour subject^ the
of the shrinking and the swelling seed lie the seed's life-
history and the cumulative effect of a multitude of inter-
relations as between the seed and the embryo, between the
kernel and its coverings, between the coverings and the
fruit, and, through the fruit, between the seed and the
parent and between the plant and its environment. It is,
therefore, obvious that we can only with some security ignore
the past when we have reason to believe that the seeds
are akin in their history ; and that is why it will be wise at
present to mainly confine our discussion of principles to the
Leguminosae. But even here it will soon be evident that
the risks increase as the affinities grow less, and the safest
road will often lie in the study of the varying behaviour of
seeds of the same species.
Proceeding on these lines, we will inquire into the constancy The con-
of these ratios in the same species, a necessary preliminary sinking the
consideration, since such estimates would lose much of their and swelling
. r , . ratios in the
value tor comparative purposes it the normal range is great, same species.
But few of the " shrinking " results admit of being stated
in this fashion, as it was my wont in most cases to weigh
3 6 STUDIES IN SEEDS AND FRUITS
a number of seeds together. Only the very large seeds
were treated individually ; and I here give the shrinking
ratios for three full-sized pre-resting seeds of Entada scandens
(all of which subsequently germinated), the weight of the
resting seed being taken as i. They were 2-46, 2-51,
and 2-62.
My method of determining the swelling ratios was better
fitted for ascertaining their range in seeds of the same species,
and the sample of results given in the table below is sufficient
to bring out their relative constancy.
Species.
Family.
Number
of seeds
Range of
the swelling
Average
tested.
ratios.
Adenanthera pavonina
Leguminosse
10
2'3O 2 '60
2-42
Cassia grandis
5
2 '04 2 '22
2-13
Entada scandens
12
2*21 2'59
2-42
Faba vulgaris (Broad Bean)
4
i '95 2 '08
2'OI
Guilandina bonducella
10
2'8o 3*26
3'08
Mucuna urens
ii
I'93 2-12
2-0 5
Poinciana regia
13
2-24 2'44
2-32
Canna indica .
Cannacese
8
I'43 I '5
1-48
shrinking
and swelling 1
ratios in
different
species.
The great The next point to notice is the great contrast which the
between the see ds of different plants display in their combined shrink-
ing and swelling capacity. Relatively to their weight some
seeds shrink and swell three or four times as much as
others. We have seen that as a general rule the water lost
in the shrinking is regained in the swelling, the one counter-
balancing the other, so that it .would be legitimate to
estimate the missing ratio where only one value has been
found. It will, however, be more convenient at first in
dealing with the great range of the capacities to speak only
of the swelling ratio, remembering of course its reciprocal
character.
In the tables the swelling capacity is stated as a ratio of
the weight of the resting seed taken as i, the reason being
that the swelling is only one-half of a reciprocal process which
is centred in the resting seed. To avoid, therefore, the in-
THE THREE CONDITIONS OF THE SEED 37
convenience of stating the values of the shrinking and
swelling in different terms, a simple reciprocal ratio was
invented, as described in a previous page. Thus, to take the
seeds of Canna indica, where the pre-resting seed loses 66
per cent, of its weight in entering the resting stage, and where
the resting seed adds 50 per cent, to its weight in swelling for
germination, the use of percentages for the two results would
be clumsy and inconvenient. But stated in. this manner :
Pre-resting seed. Resting seed. Swelling seed.
1-5 i-o 1-5
we at once get a clear view of the problem.
Now, however, when we are dealing particularly with the The employ-
swelling capacity, the usual method of stating the increase as c^ntageffn"
a percentage of the weight of the resting seed will be adopted. de >i"Jf[| oleIy
The conversion of the ratio into a percentage is simple enough, swelling
the swelling ratio of 1*5 for the seeds of Canna indica being
equivalent to an increase of weight of 50 per cent. We see
accordingly that with many Leguminosae, where the seed
swollen for germination is more than double the weight of
the resting seed, the increase amounts to more than 100 per
cent. Thus with Abrus precatorius, where the swelling ratio,
taking the resting seed as i, is 2*05, the actual increase in
weight is 105 per cent.
Looking at the extremes of the range of the swelling The range of
capacity of seeds in general, we find amongst the hundred capacity/"!)
and odd plants in the tables two groups that we can handle as r . e P/t"
sented by
fairly well, one where the absorbing capacity is not over extreme
60 per cent., the other where it is at least twice as much,
reaching 120 per cent, and over. In the first or "minimum"
group are to be included a number of plants in Table B,
such as all the Cereals, species of the cruciferous genera
Brassica and Camelina, Cannabis sativa, Pinus austriaca, and
one or two others, together with several in Table A of the
genera Anona, Canna, Citrus, Datura, Ricinus, Theobroma (Cacao),
etc., belonging in both cases to a variety of families, but,
38 STUDIES IN SEEDS AND FRUITS
if we except the species of Pithecolobium, in no instance to the
Leguminosae.
On the other hand, of the seeds of plants to be placed
in the " maximum " group, where the increase of weight is
1 20 per cent, or more, quite two-thirds are leguminous ; and
of these we may cite Adenanthera pavonina, Canavalia obtusifolia.
Cassia fistula, and species of Entada, Enterolobium, Erythrina,
Guilandina, Leuc<ena, Poinciana, etc. Belonging to a variety
of other families are the seeds of Barringtonia speciosa, Bignonia,
Ipomcea pes-capr<e. Primula, Swietenia (Mahogany), etc., which
are for the most part placed here provisionally, since only
occasionally, as with the species of Ipomcea, has the germinative
capacity been tested for individual seeds of which the shrink-
ing has been observed. Several of these probably belong
to a type of seeds where the shrinking of detached seeds
under experiment is considerably in excess of what takes
place in nature. If we were able to interrogate nature
more closely, we should probably find that the " maximum "
group would be almost entirely leguminous, thus justifying
the original view of Nobbe, which is referred to a few
pages back.
(6) by indi- We can now turn from the range of extreme groups to
specks. that of different species. Here we can -cite as extreme cases :
(a) On the " minimum " side, the seeds of Ricinus communis,
which require to absorb only 33 per cent, of their
weight in order to germinate, and the grains of
Millet (Panicum mi/iaceum), which only increase their
weight by 25 per cent, when swelling by water-
absorption ;
(b] On the " maximum " side, the different leguminous
seeds that increase their weight from 150 to rather
over 200 per cent, in taking up water for germina-
tion, such as Canavalia obtusifolia, Entada scandens,
Guilandina bonducella, and Leuc<ena glauca.
There is this much to be said concerning all cases where
the amount of water absorbed for germination is very small,
THE THREE CONDITIONS OF THE SEED 39
let us say below 20 per cent, of the weight of the resting seed,
that such seeds are on the borderland of vivipary, where they
dispense with shrinking and swelling altogether. This con-
sideration links itself with some curious reflections that are
dealt with subsequently. It is possible that we may have here
an explanation of the very low swelling capacity ascribed by
Hoffmann to a species of Raphanus (Oetrettig), viz. 8 per cent.,
which is equivalent to a swelling ratio of i'o8.
However, the ground will have to be cleared in many The causes
directions before we can expect to discover the significance of variation^
such contrasts in the swelling capacities as presented in the tables. the Celling
A tentative use of the method of exclusion may perhaps assist
us in getting into the right road ; and we will now endeavour
to ascertain if there is any connection between these contrasts
and certain conspicuous differences in the seeds. In the first
place, there is the distinction in size. This can be at once dis- (a) Distinc-
, 1 . .... , , . . tions in size
missed, since the ordinary variation in the swelling capacity and weight.
becomes almost a negligible quantity when we reflect on the
great differences in size and weight between seeds. Thus the
difference in weight between a seed of Primula verts (y^th of a
grain) and a seed of Entada scandens (400 grains) is as between
i and 40,000 ; yet the difference in their swelling ratios would
only be as between 2-3 and 2-5.
Then, again, it is possible that the distinction between
albuminous and exalbuminous seeds may supply a clue to the
variation in swelling. Exalbuminous seeds are most character-
istic of the Leguminosae ; but plants of the same family with
albuminous seeds are fairly represented in the tables. The (6) Albumin-
albuminous leguminous seeds there included have the embryo albuminous
more or less fully developed, the large, flat cotyledons being seeds -
nearly as long and as broad as the kernel. We are therefore
employing seeds where the resting period has been imposed at
much the same stage of development of the embryo. It will
be seen from the comparison made below that such differences
do not explain the great variation in the swelling capacity dis-
played by seeds of leguminous plants.
STUDIES IN SEEDS AND FRUITS
(c) Differ-
proportional
COMPARISON OF THE SWELLING CAPACITIES OF ALBUMINOUS AND EX-
ALBUMINOUS SEEDS OF SPECIES OF LEGUMINOS^E, THE RESTING
SEED BEING TAKEN AS i.
Albuminous.
Exalbuminous.
Bauhinia sp.
2 '20
Csesalpinia sepiaria
. 2 '20
Cassia fistula
2-S2
Erythrina indica
2 '49
,, grandis .
Z'll
Tamarindus indica
2-1 S
,, marginata
2'10
Abrus precatorius
. 2-05
Poinciana regia .
2'37
Entada polystachya
. 2-29
Since the proportional weight of the seed-coats vanes
greatly between different species, a subject discussed in
Chapter IX, it is possible that this may determine the varia-
tion in the swelling capacity. A cursory reference to the
results there tabulated will make it apparent that this is not
the case. This is sufficiently indicated by the comparison
made below, from which it is to be inferred that in leguminous
seeds with similar swelling capacities, the coverings may con-
stitute as little as 24 per cent., and as much as 61 per cent, of
the entire weight.
COMPARISON BETWEEN THE SWELLING CAPACITIES OF THE SEEDS OF
FOUR LEGUMINOUS PLANTS AND THEIR SEED-COAT RATIOS.
Swelling ratio.
Seed-coat ratio,
the weight of entire
seed taken as 100.
Acacia Farnesiana .
2'0
60-8
Bauhinia sp. .
Csesalpinia sepiaria .
Mucuna urens .
2 '2
2*0
6 1 '4
26-3
A noticeable feature in Table A is the small shrinking
o
(d) The seeds ratio of the seeds of moist or pulpy indehiscent fruits of the
of berries and i T t r ,
legumes. berry type. 1 was rarely successtul in getting them to
germinate ; but in the successful cases of Anona muncata (the
Soursop) and of Citrus decumana (the Shaddock), it will be seen
that the swelling ratio is similarly small, and no doubt this rule
THE THREE CONDITIONS OF THE SEED 41
generally applies. That there is a real distinction between the
seeds of berries and pods in this respect is shown in the
comparison made below ; but it will not be possible here to do
more than allude to it in passing. It will be futile to attempt
to discuss it until the relations between fruits and seeds have
been studied, a subject treated with detail in a subsequent
chapter.
COMPARISON OF THE SHRINKING AND SWELLING RATIOS (THE RESTING
SEED BEING TAKEN AS i) OF THE SEEDS OF BERRIES OR BERRY-
LIKE FRUITS WITH THOSE OF THE SEEDS OF LEGUMES.
Berries.
Legumes.
Anona muricata (Soursop)
Shr. Sw.
i '40 i i '43
Abrus precatorius .
Shr.
2-15
Sw.
2*05
,, palustris
i -45 i
Bauhinia sp. .
2'IO
2'2O
Arum maculatum .
1*63 i
Csesalpinia sepiaria .
2-25
2'2O
Citrus decumana (Shad-
Entada scandens
2-51
2'47
dock) .
1*65 i i '60
Faba vulgaris (Broac
Lonicera Periclymenum
Bean) .
2*30
2 '00
(Honeysuckle)
1 '72 i
Guilandina bonducella
3-20
3 '08
Ribes grossularia (Goose-
Phaseolus multifloru
berry) ....
i'63 i
(Scarlet-runner) .
i '90
Tamus communis .
175 i
Ulex europseus
2*30
Theobroma Cacao (Cocoa)
1-37 i
Vicia sativa
2-26
Chrysophyllum Cainito
(Star Apple)
1-45 i
Only very moist baccate fruits are here named, the seeds
of relatively dry berries losing rather more in the shrinking
process, such as those of Hedera Helix (Ivy) and Berberis, where
the shrinking ratios are 2*00 and 1*92 respectively. Bearing
this in mind, it would appear from the foregoing comparison
that whilst the seed of a moist berry when the fruit dries up
loses on the average about a third of its weight, the unripe
seed of the leguminous green pod during the shrinking pro-
cess loses as a rule rather more, and sometimes much more
than half its weight on entering the resting state.
Yet considerations such as these do not carry us very far There is
in dealing with the problem of the varying swelling ratios of "
distinc-
seeds, since it is apparent from Table B that there are whole tion j s T^ 1 not
groups of plants with dry-looking fruits, such as the Cereals
42 STUDIES IN SEEDS AND FRUITS
and the Cruciferae, where the seeds possess swelling ratios quite
as low as those of baccate fruits, and to these groups may be
added often plants with capsular fruits. There would, there-
fore, seem to be some common influence that brings not only
the seed of the berry, but the seed of the cruciferous pod, of
the capsule, and of dry-looking indehiscent fruits, into contrast
with the seed of the legume.
An appeal to We will now appeal to the varying behaviour of seeds
deviations in within the limits of a species, with the hope of discerning in
tn ei r differences some clue to the origin of the greater contrasts
seeds of the between the seeds of plants that stand apart from each other.
same species. . - , . ... _ .
We have before seen that the ordinary range or the swelling
ratios in the same plant is small ; and inquiry has led me to
believe that we shall not profit much by the study of small
differences. At times, however, there are deviations that lie
quite outside the usual range of the swelling ratios. The
cases of excessive swelling, which are probably just as apt to
occur in nature as they are in our experiments, are often readily
explained by the unusual prolongation of the swelling period
in normal seeds, which allows the seed to take up more water
than is actually needed. Both permeable and impermeable
seeds are liable at times to absorb much more freely than is
usual. Under such conditions germination usually fails ; but
occasionally it takes place, and we obtain swelling ratios far
in excess of the average. Then, again, we have cases of
excessive swelling, also ending at times in germination, where
there has been abnormal shrinking in the drying of the moist
pre-resting seed ; and since the exceptional loss of water has
to be made up in the preparation for germination, accord-
ing to the compensatory relation between the shrinking and
swelling processes before established, we find this expressed
in the increase of the swelling ratio. In these cases we are
concerned only with permeable seeds, as will be explained in
a later page.
On the other hand, we have instances of swelling ratios con-
siderably below the average and equally outside the ordinary
THE THREE CONDITIONS OF THE SEED 43
range. This happens in the case of impermeable seeds where
the shrinking process has been incomplete, and considerably
less water is required for germination than in the instance of
the typical resting seed.
I will first take those cases of excessive swelling displayed First, to the
L i j 1-111- -i i 1 j excessive
at times by normal seeds, and will begin with permeable seeds, swelling
to which indeed earlier investigators seem to have mainly con- ^meshy* &t
fined their inquiries. Dr Nobbe inferred that as a rule seeds normalseeds.
require to be well soaked for germination, and that those
cases where complete soaking is not necessary are exceptional
(pp. ii 8, 119). But he remarked that the minimum amount
of water needed to start the germinating process was a subject (a) By per-
, c . f ^ . . r . 1-j- meable seeds,
tor future inquiry (p. 120). It is, in tact, in this direction
that later investigators have worked, and it is now possible to
distinguish between
(a) The minimum amount of water required for starting
germination,
() The average amount that seeds absorb under natural
conditions in swelling for germination,
(c) The amount of water required for saturation.
The quantity of water that a seed absorbs before germinat-
ing under natural conditions, or in ordinary germination
experiments, is considerably above the minimum amount
needed, and markedly below the amount requisite for the
seed's saturation. A rough indication that leguminous seeds
germinate before they are saturated is found in the fact that
normally seeds germinate long before they rupture their coats,
which is the sign of the seeds being thoroughly soaked with
water. (I refer to ruptures taking place away from the hilum.)
Minimum results can, of course, be only obtained in the
laboratory. By an ingenious course of experiments, referred
to in Note 4 of the Appendix, Victor Jodin established a
" germinative minimum " for Peas (Pisum sativuni), and in his
paper he quotes similar estimates made by Van Tieghem for
" Feves " (I suppose, Broad Beans, Faba vulgaris). The results,
which are stated in different fashions by the various investi-
44
STUDIES IN SEEDS AND FRUITS
(6) by imper-
meable seeds.
gators, have all been converted into percentages of the weight
of the resting seed carrying its normal water-contents.
COMPARISON OF THE MINIMUM AMOUNT OF WATER REQUISITE FOR
GERMINATION, AND OF THE AVERAGE QUANTITY ABSORBED UNDER
NATURAL GERMINATING CONDITIONS, WITH THE MAXIMUM AMOUNT
THAT A SEED CAN TAKE UP, i.e. THE AMOUNT NEEDED FOR
SATURATION. (Stated as percentages of the weight of the normal
resting seed.)
Pisum sativum.
Faba vulgaris.
Minimum for germination
Average for germination
Maximum (for saturation)
6 7 J; 7 iN
91 G; 107 H ; 96 N
no G
74 T.
95 G ; 104 H
120 G ; 118 T
G=Guppy. H = Hoffmann. J=Jodin. N = Nobbe. T = Van Tieghem.
I have endeavoured here to give the general run of the
results. The critical results are of course those made by the
same investigator on the same set of seeds. Thus we notice
particularly in the case of " Feves " (assumed above to be Faba
vulgaris} Van Tieghem's estimate of 74 per cent, as the
minimum amount of water required for germination and 1 1 8
per cent, as the maximum amount that a seed can absorb. So
again my own results for Faba vulgaris (Broad Beans) were
very definite, 95 per cent, being the average for germination
and 1 20 per cent, the amount needed for saturation. The
general indications above afforded for seeds of the types of
the Pea (Pisum} and the Bean (Faba) clearly show that whilst
the minimum amount of water required for germination is
about 70 per cent, of the weight of the resting seed, a con-
siderably larger quantity of water is needed for saturation, viz.
no to 1 20 per cent. Between these two extremes lie the
average amounts of water required for germination under
ordinary conditions, as determined from the observations of
Hoffmann, Nobbe, and myself.
The seeds of Pisum sativum and Faba vulgaris are typical
permeable seeds. Similar indications were presented in many
of my experiments on impermeable seeds of the same family.
THE THREE CONDITIONS OF THE SEED 45
Thus, a seed of Entada scandens weighing 400 grains in the
resting state will be ready to germinate under normal condi-
tions when it has increased its weight by water-absorption to
from 950 to i ooo grains. But if the conditions are unfavour-
able and it fails to germinate, it will continue absorbing water
until it reaches a condition of saturation, when its weight will
be about 1 1 50 or 1 1 60 grains. Thus :
Water required stated as a
percentage of the weight
of the resting seed.
Swelling ratios, taking the
resting seed as i.
For
germination.
For
saturation.
For
germination.
For
saturation.
Entada scandens .
140 to 150 %
'9 %
2 '4 to 2 '5
2-9
In other experiments seeds often continued to absorb water
long after they had failed to germinate. They may occasion-
ally germinate when the swelling ratio has far exceeded the
normal limits, but only in an imperfect and belated fashion.
One or two more instances will serve to illustrate these points.
A seed of Albizzia Lebbek, i grains in weight, only requires to
increase its weight to 4*5 grains in order to germinate ; but
when it has failed to germinate it will continue absorbing
water without rupturing its coat until nearly 6 grains in weight,
the limits of the normal swelling ratio, 2-25, being long passed.
So, again, a permeable seed of Entada polystachya, weighing
7 grains, germinates usually after its weight has been increased
by the absorption of water to about 1 6 grains, its swelling ratio
being 2*3 ; but when it fails it continues to swell and reaches
a weight of 2 1 grains and over, thus tripling its original weight
to no purpose. Convolvulaceous seeds, possessing in the
resting stage a hard, dry albumen, are especially liable to take
up more water than is needed for germination. In its transi-
tion into the mucilaginous state, the albumen absorbs a very
large amount of water. The normal swelling ratio for a seed of
Ipomcea pes-capr<e is about 2-5, but seeds may germinate tardily
46 STUDIES IN SEEDS AND FRUITS
after their weight has been increased threefold, and seeds that fail
to germinate sometimes acquire 3^ times their original weight.
When we come to deal with the hygroscopicity of seeds
we shall be able to state precisely the lower value of the seed's
hydratation, that is to say, below the minimum required for
germination. This is the " hygroscopic maximum " (see
Chapter VII).
Second, to Coming to the second kind of excessive swelling, we deal
^enSg^r 6 ner e with seeds abnormally shrunken, when the excess of
abnormally water absorbed in the swelling process compensates for the
permeable excess lost in the shrinking stage. But it should be noted
that we are not here concerned with seeds so much shrunken
that they have lost their vitality, a fate that may befall
permeable and impermeable seeds alike, but with seeds that
still retain their germinating powers. Thus it comes about
that permeable seeds alone illustrate this type of excessive
absorption, since defective shrinking acts in different ways on
the swelling capacity of seeds, according to their permeable or
impermeable character in the resting state. If permeable, the
shrinking is too great, and the swelling is also excessive. If
impermeable, the shrinking is deficient and the swelling ratio
is much reduced. This is in accord with the compensatory
principle before established, that what the shrinking seed loses
the swelling seed gains. But it is important to notice that we
are here again brought face to face with the distinction between
permeable and impermeable seeds.
Permeable seeds that are allowed to dry when detached
from the plant in the full-sized moist condition generally
shrink too much ; and as a rule they fail to germinate, absorb-
ing much more water in proportion to their weight than in
the case of the normal resting seed. Greatly shrivelled seeds
are, as is manifest, imperfectly developed, so that they scarcely
call for our attention. However, to illustrate this subject,
I give below my observations on the seeds of Canavalia
ensiformis in three conditions : excessively shrivelled, moderately
shrivelled, and normal.
THE THREE CONDITIONS OF THE SEED 47
COMPARISON OF THE SHRINKING AND SWELLING RATIOS OF THE SEEDS
OF CANAVALIA ENSIFORMIS UNDER DIFFERENT CONDITIONS.
Condition of seed.
Weight in grains.
Ratios, taking
the resting
seed as i.
Germinative
capacity.
Excessively shrivelled .
Moderately ,,
Normally contracted .
Jtfng. * SwoHen.
44-1 15-0 39-0
6o'o 25-5 597
48'3 23*3 4 6 '6
Shr. Sw.
2*94 i 2 -60
2-36 I 2-34
2 '07 I 2'OO
Lost.
Usually retained.
Normal.
Those cases where seeds of the same species at times
display much diminished swelling capacities, as expressed in
swelling ratios considerably below the average and outside the
ordinary range of variation, now claim our attention. Such
cases are peculiar to impermeable seeds, and occur when the
shrinking process is incomplete, less water being required for
germination, since less than the normal amount is lost in the
shrinkage. This is a point of considerable importance, and
one on which much of my work has been concentrated, since
it supplies the key to one of the principal positions maintained
in these pages. We get here our first glimpse at the signifi-
cance of impermeability, and we perceive how it comes about
that both permeable and impermeable seeds may be found in
the same species.
Very interesting indications in this direction are sup-
plied by the seeds of Guilandina bonducella, and I will briefly
state the general results of numerous observations made
o
in Jamaica. When we open the full-grown green pods
of this plant we find two kinds of soft green pre-resting
seeds :
(a) Yellowish green soft seeds, about 100 grains in weight
and 25 to 27 millimetres in diameter, which represent
the maximum development in size and weight of
the pre-resting seed before the shrinking process
commences.
Third, to the
great diminu-
tion of the
swelling
capacity
caused by
the deficient
shrinkage of
impermeable
seeds as
illustrated,
(a) by Gui-
landina
bonducella,
48 STUDIES IN SEEDS AND FRUITS
(b) Dark olive-green soft seeds, rather firmer than those
above, 94 or 95 grains in weight, 23 to 25 mm. in
diameter, and representing the pre-resting seed in
the earliest stage of shrinking.
If we open other pods that are commencing to wither we
find the seeds in various stages of contraction ; and finally we
come upon the dried-up brown dehiscing pod containing hard,
grey impermeable seeds very much smaller than those of the
a and b stages, and weighing 33 or 34 grains.
Such is Nature's method, provided we do not interfere
with it. But if we remove from the green unopened pod
seeds in the a and b stages and allow them to dry on the table,
we get the following results. The fully formed pre-resting
seed of the a stage shrinks excessively, and when that process
is complete we find a greatly shrivelled seed, weighing 27 or
28 grains, which takes up water readily, yet fails to germinate.
But if we take one of the olive-green b seeds, where shrinking
has already commenced, and allow it to dry on the table under
the same conditions, we notice that instead of shrinking exces-
sively its shrinkage as compared with that of the normal resting
seed is deficient, and that instead of weighing about 33 grains,
as it would have done if it had been left undisturbed in the pod,
its final weight is as much as 42 grains. Such a seed, though
permeable and hygroscopic, retains its germinative capacity.
Now comes the critical part of the experiment. If we put
the greatly shrivelled a seed in the conditions for germinating,
we find that whilst it swells excessively by absorbing water and
increases its weight by about 230 per cent., it fails to germinate.
On the other hand, the b seed, which has shrunk deficiently,
absorbs water easily, increases its weight by about 150 per
cent., and germinates healthily. Very different is the behaviour
of the normal resting seed. Its impervious outer coat has to
be filed through before it can take up water for germination ;
and before that stage is reached it increases its weight by about
200 per cent.
But the important point as indicated in the results tabulated
THE THREE CONDITIONS OF THE SEED 49
below is that the two germinable seeds, the permeable,
deficiently shrunken seed and the normal, impermeable seed,
when swelling for germination, take up much the same amount
of water that they surrendered in the shrinking process. In
other words, the needs for germination are satisfied by the
seed's regaining the water previously lost, the permeable seed
taking least and the impermeable seed most. This is well
brought out in the ratios given in the table ; and thus we see
how, without impairing the germinative powers, deficient
shrinkage leads to decrease in the swelling capacity and to the
loss of impermeability.
TABLE SHOWING THE DIFFERENT EFFECTS OF EXCESSIVE, DEFICIENT,
AND NORMAL SHRINKAGE ON SEEDS THAT ARE TYPICALLY IMPER-
MEABLE IN THE RESTING STATE, AS ILLUSTRATED BY THE RESULTS
OF EXPERIMENTS ON THE SEEDS OF GUILANDINA BONDUCELLA.
Shrinking
Condition of
the resting
seed.
History of the
seed.
Weight in grains of the
pre-resting, resting,
and swollen seed.
and swelling
ratios, the
resting seed
Effect on the
seed.
as i.
Pr*>
R-ct
Swollen
i re-
resting.
cSI"
ing.
for germi-
Shr. w.
nation.
A. Excessively
Detached from
IOO
28-5
92
3-50 I 3-30
Permeable and
shrunken
the green
pod before
hygroscopic,
germinative
shrinking
powers lost.
had begun
B. Deficiently
Detached from
IOO
42 'o
105
2*38 I 2*50
Permeable and
shrunken
the green
hygroscopic,
pod in the
germinative
early stage
powers re-
of shrinking
tained.
C. Normally
Shrinking pro-
IOO
33'3
IOO
3 'oo i 3 - oo
Impermeable
contracted
cess carried
and normal
out in the
in all re-
pod on the
spects.
plant
The shrinking ratio for the normal resting seed was mainly obtained by comparing
the average weights of seeds in different stages of contraction on the same plant.
The weight of the resting seed averages nearly 40 grains ; but for convenience in
stating the ratios the weight of 33 grains is employed in the table and in the text.
The important lesson of the seeds of Guilandina bonducella
in this matter is that decrease in the swelling capacity is
4
5 c STUDIES IN SEEDS AND FRUITS
associated with the loss of impermeability, and that these results
are primarily due to the deficient shrinkage of the pre-resting
seed. In my experiments other impermeable seeds behaved
like those of Guilandina bonducella. When they had lost their
impervious character they swelled less and in consequence
required less water for germination. The loss of imper-
meability was in fact associated with marked diminution in the
(6)byDioclea swelling ratios. A good example of this result was afforded
xa> in the case of the seeds of Dioclea reflexa, gathered by me in the
woods of the Grand Etang in Grenada, their mode of occur-
rence being described in Chapter V. Here the origin of the loss
of impermeability could be readily traced, and the permeable
seeds were easily recognised by their larger size, darker hue,
softer coverings, and by other indications of deficient shrinkage.
The outcome of a number of observations was as follows :
The permeable seeds of Dioclea reflexa in swelling for germi-
nation increase their weight by about 80 per cent ; whilst the
impermeable seeds just double their weight. This difference
is not so great as in other impermeable seeds, since the seed-
coverings act somewhat irregularly, as described in Chapter IX.
If the share taken by the coats in the swelling process is
eliminated, the contrast between the swelling capacities of
these two types of seeds is made more evident, the kernel of
the permeable seed showing an increase of weight of about
80 per cent., and that of the impermeable seed of about 130
per cent. The swelling mechanism of these seeds is discussed
in Chapter IX.
The behaviour of the seeds of Guilandina bonducella and
Dioclea reflexa must be typical of many other leguminous seeds
with impervious coats. Any influence that impedes the
shrinking of the soft seed of the green pod tends to prevent
the acquirement of impermeability. One may cite in this
connection the seeds of C<esalpinia sepiaria and C<esalpinia
Sappan^ which are often impermeable when allowed to ripen
on the plant, but permeable if they have been prematurely
detached from the pod, as described in Chapter V.
THE THREE CONDITIONS OF THE SEED 51
Sometimes these deviations from the normal behaviour of
a seed become fixed ; and Nature then facilitates our inquiries
by presenting in the same species two types of seeds which are
distinguished not only in size and colour, but also by their
different degrees of impermeability. Such seeds have also
two corresponding degrees of swelling capacity, the permeable
seeds requiring much less water than the impermeable seeds.
Entada polystachya, as observed by me in Grenada, is a case of
this kind. Here we find two types of seeds differing from
each other in almost all the critical points that distinguish
permeable and impermeable seeds, and equally capable of
reproducing the plant. As indicated in the table below, they
differ in colour, size, and weight, as well as in their swelling
capacity, the permeable seed increasing its weight by about
124 per cent, before germination, whilst the impermeable seed
requires more water and adds 1 50 per cent, to its weight.
COMPARISON OF THE TWO TYPES OF SEEDS PRODUCED BY
ENTADA POLYSTACHYA
(c) Entada
polystachya,
which dis-
plays the
same prin-
ciple in its
two types of
seeds.
Type.
Colour.
Length and
breadth.
Resting
weight.
Shrinking and swelling.
Weight in grains.
Ratios.
Unripe. ^ st " Swollen.
Shr. Sw.
A. Large and
permeable
Yellowish
brown
15 x 12 mm.
6 '6 grs.
14-8 6'6 14-8
2*24 I 2'24
B. Small and
impermeable
Dark
brown
13x11 mm.
5-ogrs.
12-5 5-0 12-5
2*50 I 2*50
Different hypotheses present themselves in explanation of
this relation between the swelling capacity and the permeability
of a seed. For example, it may be suggested that it is merely
a matter concerned with the water-contents or hydratation of a
,seed, a view that would accept, without explaining, the impli- The question
cation of these experiments, that impermeable seeds contain ^
less water than permeable seeds. To form an opinion
would be to prejudge a matter which will prove to be far more way.
now permeability
UW blocks the
52 STUDIES IN SEEDS AND FRUITS
complex than it at first appears. This question of the ability
or inability of seeds to absorb water through their coats has
been constantly arising in this chapter in connection with
other seed -capacities ; and in the particular subject we
have just been considering it is manifestly impossible to
make further progress until we investigate the nature of
the differences associated with the distinction between a
permeable and an impermeable seed. At present, there-
fore, the question of permeability and impermeability blocks
the way. We will accordingly proceed to its discussion
in the next three chapters.
SUMMARY
(1) We deal here with the three conditions presented by the large, soft
pre-resting seed, the hardened, contracted resting seed, and the soft,
swollen seed about to germinate (p. 18).
(2) This involves the study of the shrinking and swelling of the seed,
processes which are in the main concerned with water-loss and water-
gain (p. 19).
(3) The balance is the instrument of this investigation, and the modes
of thus determining the shrinking and swelling ratios are described
(p. 20).
(4) The indications of the single seed, when its history has been
followed in all three conditions, prove that the water lost in shrinking
is regained in swelling for germination, and that the swollen seed
represents the return to the pre-resting or so-called unripe state
(p. 21).
(5) The same reciprocal relation between the shrinking and swelling
processes is established by independent observations of the three
conditions on a large number of different seeds (p. 22).
(6) The principle that the water lost in the shrinking process is
gained back in the swelling stage was accepted by Dr Nobbe in his
Handbuch der Samenkunde^ 1876 (p. 23).
(7) Tables of the shrinking and swelling ratios are given, the first
containing the results of the author's observations, the second those
of Hoffmann and Nobbe (pp. 2427).
(8) It is then pointed out that the essentially mechanical nature of
the shrinking and swelling processes is involved in their reciprocal
character (p. 29).
THE THREE CONDITIONS OF THE SEED 53
(9) Additional proofs of the mechanical nature of the swelling process
are indicated as follows :
(a) By the fact that when a seed on the eve of germination is
dried, it returns approximately to its original weight as a
resting seed. The results of a number of experiments on
leguminous seeds are given, and it is shown that seeds fall
short of or exceed the original weight according as they were
in the first place permeable or impermeable (p. 30) ;
(b) By the fact that the weight-relations of coats, kernel, albumen,
and embryo are much the same in the seed dried after swell-
ing for germination as they are in the resting seed ; illus-
trated by examples (p. 31) ;
(c) In the ability of the embryo in many pre-resting seeds to pass
at once to germination without the intervention of the
resting stage, such embryos being potentially viviparous
(P- 32).
(10) Neither the large, soft pre-resting seeds nor the seeds swollen for
germination are in a condition of saturation (p. 33).
(n) The shrinking and swelling ratios are then more closely con-
sidered (p. 34).
(12) The views of Dr Nobbe (p. 34).
(13) The difficulties of the subject, and the necessity of confining the
discussion of principles to one family, namely, the Leguminosae
(P- 35)- ,
(14) The constancy of the shrinking and swelling ratios of normal
resting seeds of the same species is then shown (p. 35).
(15) But the contrast, as exemplified by the swelling ratios, is great
between difFerent species, whether in groups or in individuals. Thus,
the Cereals with a swelling capacity of not over 60 per cent., and the
Leguminosae with a capacity ranging between 90 and 2OO per cent.,
represent the minimum and maximum groups. That leguminous
seeds possess the highest capacity for absorbing water when preparing
for germination was stated long since by Nobbe. The contrast
between individual species is displayed by the seeds of Ricinus communis
and of Guiland'tna bonducella, the first adding only one-third to their
weight, and the last trebling their weight when swelling for germin-
ation. Seeds that possess a very low swelling capacity, for instance,
below 20 per cent., are probably on the borderland of vivipary
(PP. 3 6 ~3 8 )-
(16) The reasons of the great range in the swelling capacities of
difFerent seeds are then considered, that is to say, why the seeds of some
plants absorb much water and others very little in swelling for germina-
tion. After endeavouring to ascertain whether there is any connection
between this great variation, and certain conspicuous difFerences in
54 STUDIES IN SEEDS AND FRUITS
seeds, such as distinctions in size and weight (p. 39), the albuminous
or exalbuminous character of seeds (p. 39), differences in the propor-
tional weight of the seed-coats (p. 40), the difference in the types of
fruits, as between berries and legumes (p. 41), etc., it is inferred that
there is much which these distinctions will not explain (p. 41}.
(17) Appeal is then made to the unusual deviations in the swelling
capacity of seeds of the same species, with the hope of finding a clue to
the origin of the great contrasts in this respect presented by the seeds
of different plants (p. 42).
(18) In the first place, cases of excessive swelling in normal resting
seeds are discussed, both of the permeable and impermeable types ; and
it is pointed out that it is possible to distinguish between
(a] The minimum amount of water required for germination as
shown in laboratory experiments ;
(b] The average amount of water that under natural conditions
seeds absorb when swelling for germination ;
(c] The maximum amount of water that seeds can absorb to
produce saturation, the seed continuing to take up water
long after it has failed to germinate (pp. 4345).
(19) In the next place, reference is made to the case of excessive swell-
ing in abnormally shrunken resting seeds where the absorbing process
is compensatory, the unusual loss of water in the shrinking process
being thus supplied. But such seeds, whether in the normal condition
permeable or impermeable, have lost their germinative powers, and as
such have no concern for us here. Seeds that shrivel much, absorb
much, but do not as a rule propagate the species. This is usually the
fate of seeds that are removed from the green pod in the soft, full-
grown pre-resting state before shrinking has begun. But with imper-
meable seeds it sometimes happens that such seeds shrink less when
allowed to go through the shrinking process detached from the plant
than when left undisturbed in the pod. If we wait until shrinking
has just begun before detaching the seed from the plant, this deficiency
in the shrinkage is the rule. Such seeds retain their germinative
powers, but their shrinking has been deficient ; and, according to the
compensatory principle that what the shrinking seed loses the swelling
seed gains, their capacity of absorbing water for germination is propor-
tionately reduced. They are larger and heavier than the normal
impermeable seeds, and take up water easily (p. 46).
(20) When, therefore, we come to appeal to cases of unusual diminu-
tion of the swelling capacity in resting seeds, we find that examples are
only supplied by abnormal impermeable seeds. Here the shrinking
process is incomplete, and in consequence less water is required for
germination than in the normal resting seed. This unexpected
contrast between the behaviour of permeable and impermeable seeds when
THE THREE CONDITIONS OF THE SEED 55
they are detached in the soft pre-resting state from the green pod, and
allowed to go through the shrinking process removed from the parent,
brings us face to face with the significance of the impermeability of
seeds. A great deal lies behind the fact that under such conditions
with a permeable seed the shrinking is too great and the subsequent
swelling for germination excessive, whilst with an impermeable seed
the shrinking may be deficient and the swelling ratio much reduced
(P- 47)-
(21) Illustrations of the behaviour of impermeable seeds in this respect
are afforded by those of Guilandina bonducella and Dioclea reflexa^ where
deficient shrinkage of the large, moist pre-resting seeds leads to a
corresponding decrease in the normal swelling capacity and to the loss
of impermeability ; and by those of Entada polystachya^ which displays
in its two types of normal seeds, permeable and impermeable, a small
shrinking capacity and a small swelling ratio for the first, and a large
shrinking capacity and a large swelling ratio for the second (pp. 4751).
(22) Experiments on seeds of the impermeable type in their soft pre-
resting condition therefore indicate that a diminution of the shrinkage
prevents the acquirement of impermeability and at the same time
lessens the amount of water required for germination. This strange
relation between the amount of water a seed absorbs in preparing for
germination and the permeability or impermeability of the seed-
coverings renders necessary an investigation of the distinctive characters
associated with these two types of seeds. The question of permeability
and impermeability, therefore, blocks the way (p. 52).
CHAPTER III
THE IMPERMEABILITY OF SEEDS AND ITS SIGNIFICANCE .
THE impermeability of seeds has occupied the attention of
many able investigators, but usually in connection with some
other character. They have not, however, always been in
agreement as to the meaning to be attached to the term
" impermeable," a fundamental difference which is reflected
in their occasionally inconsistent conclusions. In this work
a seed is regarded as impermeable only when it is able to
resist the penetration of water during an immersion of weeks
or months.
Nature supplies abundant evidence of the impermeable
character of certain seeds in the floating drift of ponds and
rivers and of the ocean currents ; and many inquirers in their
observations and experiments on seed -buoyancy have dealt
indirectly with this subject ; but as it would be out of place
to allude to their results here, I would refer the reader for
a detailed treatment of the matter to my book on Plant
Dispersal. It should, however, be remarked that imperme-
ability may be equally a quality of the seed that sinks and
of the seed that floats, its connection with buoyancy being
only of an indirect character.
I will at once proceed to deal with some of the aspects of
the subject, on which recent investigations have thrown light.
The fre- The frequency of impermeability in the case of seeds of certain
permeability." families, especially among the Leguminosae, was established
by Nobbe a generation ago in the pages of his work on
56
THE IMPERMEABILITY OF SEEDS 57
seeds, Handbuch der Samenkunde ; and he it was who pointed
out that even with plants where all the seeds seemed to be
permeable, there might be a small residuum of 2 or 3 per cent,
that continued to resist the penetration of water even after
some months' immersion (pp. 112, 113). But this botanist
made no special study of the subject, except in so far as it
was in relation to other seed-characters.
It is to a recent Italian investigator, Dr Guiseppe Gola, Itsinvesti-
that we are indebted for an extensive series of studies of the Dr Gola.
nature and prevalence of this quality. His memoir, which
is entitled Ricerche sulla biologia e sulla fisiologia de Semi a
tegumento impermeabile, and which was published by the
Royal Academy of Sciences of Turin in 1905, will come as a
surprise to many who, like myself, were unaware that im-
permeable seeds are so frequently to be met with in the
plant-world. Although not able to follow him in all his
conclusions, I have found in his data the materials for a solid
foundation on which to begin in these pages a discussion of
the subject of impermeability.
After ascertaining by a preliminary inquiry that this character
was exhibited most markedly by the seeds of Leguminosae
and then by those of Cistaceae and Malvaceae, Dr Gola
decided to limit his researches to those three families. His
method was well adapted to test the capacity of seeds in this
respect, since they were kept immersed in water for periods
of between thirty and eighty days. When swelling occurred,
it took place generally in from three to five days, and less
usually in about ten days. Impermeable seeds remained
unaffected at the end of the trials. The seeds of about 300
species of plants were exposed to this test, of which about 260
(belonging to 45 genera) were leguminous, whilst nearly
30 belonged to the Cistaceae, and 10 were malvaceous.
Temperate genera greatly predominate in his list of results,
not merely numerically, but also in the number of species
tested. Including the Acacias, we may here mention the genera
Astragalus, Cytisus, Genista, Lathyrus, Lotus, Medicago, Melilotus,
58 STUDIES IN SEEDS AND FRUITS
Trifolium^ Vicia^ etc. As a rule between 50 and 100 seeds
of each species were experimented on, and the percentage
of permeable seeds is recorded in a special table.
On tabulating the results given by Dr Gola for the
Leguminosae and Cistaceae in the manner shown below, I
was surprised to learn how common it was to find permeable
and impermeable seeds in the same species.
TABULATION OF THE RESULTS FOR THE LEGUMINOS^E AND CISTACEJE
GIVEN BV DR GOLA IN HIS TABLE SHOWING THE PERCENTAGE OF
PERMEABLE SEEDS IN THE SAME SPECIES.
Number
of
species.
Species with no
seeds permeable.
Species with all
seeds permeable.
Species with both
permeable and im-
permeable seeds.
Number.
Per-
centage.
Number.
Per-
centage.
Number.
Per-
centage.
Leguminosse
Cistacese
260
2 7
17
o
7
40
15
o
203
27
78
IOO
Permeable We see here that 78 per cent, of the species of Leguminosae
meab^ P seeds possessed both permeable and impermeable seeds, those with
commonly ^\\ see d s impermeable or with all seeds permeable amounting
same species, to J and 15 per cent, respectively. The proportions of each
kind of seed in a species were in most cases fairly constant,
the results for two different samples being as a rule not far
apart. Within the limits of a genus the species exhibited
great contrasts in their proportions of permeable and im-
permeable seeds. Almost all the leguminous genera that
are best represented in Dr Gola's table show variations
ranging between the two extremes : (a) of species with all
seeds permeable, and () of species with all or nearly all seeds
impermeable, none containing exclusively species possessing
one type of seed. Not one of the leguminous genera which
are here represented by ten or more species could be designated
as exclusively characterised by permeable or impermeable seeds.
THE IMPERMEABILITY OF SEEDS
59
All are variable or " mixed " in this respect. It would thus
appear from the results of the investigations of Dr Gola
that impermeability with the Leguminosae is not usually
a distinction between species, and hardly ever between
genera.
But although the leguminous genera best represented in
the table of Dr Gola are " mixed " in the sense that not one
of them can be described as exclusively possessing species
with one type of seed, they may differ in degree considerably
from each other. The average proportions of permeable and
impermeable seeds for the species of the three genera, Acacia,
Astragalus^ and Lathyrus, are given below ; and from the
tabulated results it appears that in order of impermeability
Acacia stands first, with an average of 83 per cent, for a species,
and Lathy rus last, with an average of 20 per cent.
AVERAGE NUMBER OF PERMEABLE AND IMPERMEABLE SEEDS IN THE
SPECIES OF THREE LEGUMINOUS GENERA. (Tabulated from data
given in Dr Gola's Memoir.)
Impermea-
bility not a
generic char-
acter, though
more charac-
teristic of
some genera
than of
others.
Number
of species
tested.
Average percentage for a
species.
Permeable
seeds.
Impermeable
seeds.
Acacia
Astragalus
Lathyrus .
20
43
20
35
80
83
65
20
In the same way, with regard to species of Leguminosae,
it would seem that although as a rule, that is in 80 per cent.
of the plants, we cannot employ the presence or absence of
impermeability in the seeds as a specific distinction, yet species
differ very much in the proportion of impermeable seeds that
they possess.
Such, then, are the preliminary conceptions with reference
to impermeability that one forms from the data obtained by
Dr Gola. These conceptions will be considerably extended
60 STUDIES IN SEEDS AND FRUITS
as one follows the trend of still more recent investigations.
However, I pass over for a time the results of the brilliant
The re- researches of Paul Becquerel, carried out in the laboratory of
BecquereL tne Sorbonne between 1904 and 1907, because in as far as
they deal with matters discussed in these pages they are
primarily concerned with the impermeability of seeds to air,
and will be more appropriately referred to in the chapter on
the hygroscopicity of seeds.
Mr Crocker In following the history of the investigation of this subject
elation 'ofkn- from the data at my disposal, the next advance on solid ground
P e ."eability seems to be that supplied by the results obtained by Mr
longevity of Crocker. If Dr Gola opened our eyes as to the frequency
of impermeability in the seed-world, Mr. Crocker has done
much to enlighten us as to its biological significance. In
different papers published in the Botanical Gazette (Uni-
versity of Chicago Press, 1906-9) he expresses the opinion
that " delayed germination," or, as we might term it, " seed-
longevity," is more generally due to seed -coat characters
"limiting or entirely excluding water or oxygen -supply"
than to embryo characters or the " so-called dormancy of
protoplasm." His results go far to establish the view put
forward by Nobbe and Hanlein in 1877, and quoted by
him, that " delayed germination is due in many cases to
the impermeability of the seed-coat to water." One of his
papers (" Role of Seed-coats in Delayed Germination," October
1 906) is concerned especially with this point ; but he repeats
the general conclusion formed, as above given, in a later paper
("Germination of Seeds of Water-plants," November 1907),
and in a short article in the same publication in January 1909.
It may be remarked before concluding this reference that Mr
Crocker regards impermeability to water as much more con-
ducive to seed-longevity than imperviousness to oxygen (ibid.^
October 1 906) ; and this is the point that is of most interest to
us in the present stage of this discussion. " The coats that
exclude water" (he writes) "are undoubtedly much better
adapted to securing a long delay."
THE IMPERMEABILITY OF SEEDS 61
It is to Professor Ewart of the University of Melbourne The investi-
, . , , , f . ., gations of
that we are indebted tor a most important contribution to our p ro f. Ewart.
knowledge of seed-longevity and of the impermeability of the
seed-coverings. If the author had had the leisure to extend
the explanatory portion of his memoir, it would have ranked
as one of the most extensive records of investigations con-
cerned with seeds since De Candolle published his Geographic
botanique rather over half a century ago. Dr Gola and Mr
Crocker, as far as the dates of publication are concerned, were
his predecessors in the field ; but it would be probably more
correct to say that they were contemporaries in their labours.
Professor Ewart, like Dr Gola, discusses the distribution of
impermeability in seeds, and, like Mr Crocker, he considers
the relation between longevity and impermeability. But on
this point the two investigators in America and Australia seem
to diverge widely, Mr Crocker holding that u delayed ger-
mination is generally related to seed-coat characters rather than
to the so-called dormancy of protoplasm," whilst Professor
Ewart considers that longevity depends not on the seed-coats,
but on the staying power of the protoplasm. The difference,
however, is more apparent than real, since Professor Ewart
evidently regards the impermeable covering as an adaptation
for ensuring the long life of the seed in the soil ; and at
all events it would seem likely there is enough common
ground on which to base a theory that would reconcile both
the views.
In this memoir on " The Longevity of Seeds," which was
published in the Proceedings of the Royal Society of Victoria for
1908, he deals with the seeds of about 2500 species of
plants. In addition to the results of his own work, which
involved the employment of nearly 3000 tests, Professor Ewart
incorporates in his table, which in itself occupies 176 pages,
all the previous records relating to the subject that he could
find. Yet, in spite of the great importance of this contribution
to knowledge, one is conscious of missing much in the 22
pages that are alone devoted to the summarising of results,
62
STUDIES IN SEEDS AND FRUITS
The relation
between im-
permeability
and
longevity.
since a very large amount of interesting, if subsidiary, matter
finds no expression either in the table or in the text.
Professor Ewart arrives at the conclusion that " macrobiotic "
seeds (as he terms seeds that may last from 15 to over 100
years) are characterised by " more or less impermeable coats,
and are restricted to a few natural orders, of which the
Leguminosae greatly surpass all others, whilst Malvaceae
and Myrtaceae come next in importance." The general
trend of the curves, he remarks, indicates that the extreme
duration of vitality, probable for any known seed, lies between
150 and 250 years. The number of species in the list of
plants characterised by macrobiotic seeds amounts to 180,
which is less than I per cent, of the total number of species
experimented upon ; and of these about 75 per cent, are
leguminous. Sixty per cent, or 30 out of the 50 species of
Acacia included in the general table possess these long-lived
seeds ; and since impermeability and longevity are so closely
associated in this genus, we may recall here the high average
of impermeability assigned above to seeds of species of Acacia
from data supplied in Dr Cola's tabulated results. There
is naturally no attempt here to deal with the general question
of impermeability, except in its relation to longevity ; and the
method of stating the results in the table rarely allows me
to draw such inferences for myself with security. Still, some
general principles of much importance are indicated in the
text and in the table ; and they may be here alluded to.
In the first place, as was previously implied by Mr Crocker,
the impermeability of seeds to water exhibits itself as an
adaptation for ensuring the long life of the seed in the soil.
It is not essential for securing the longevity of seeds in air.
Professor Ewart points out that some seeds with readily per-
meable coats, such as those of species of Phaseolus and Triticum^
may retain their vitality for many years in dry air. This
being the case, it follows that the experiments, based as they
chiefly are on seeds that have been kept in dry air for a
varying number of years, are mainly concerned with the
THE IMPERMEABILITY OF SEEDS 63
longevity of seeds under those conditions. The question
whether impermeable seeds will preserve their vitality longer
in the soil seems to be as yet unanswered. Although, as The question
, . , . T-V i i -i r whether im-
quoted in this paper, Duvel has shown that in the case or permeable
ordinary seeds the advantage lies with seeds dried in air, he preserve 11
did not determine this point for the hard seeds that did not J heir vitality
. f longer in the
germinate in his experiments, apparently, as Professor Ewart soil than in
observes, because he did not employ methods that would fully
test their germinative capacity. Commenting on the results
of the extensive experiments of Duvel and Waldron to deter-
mine the length of time weed-seeds must be buried in order
to lose their vitality, Crocker points out that " vitality tests of
this kind, that neglect the effect of the seed-coats, are tests of
the condition of the seed-coats rather than tests of the real
vitality of the embryos themselves " (Botanical Gazette, October
1906). In this connection the testimony of Professor Pammel
of Iowa is significant. As concerning the seeds of a number of
weeds, he found that the percentage of seeds germinating was
lower and the dormant period longer if the seeds were kept
during the winter in paper packages than if they were placed
in sand and exposed to the climatic conditions of an ordinary
winter (Brit. Assoc.^ 1909, "Nature," October 28, 1909).
It is nevertheless evident from the Australian observations
that even the most resistant of seeds tend to lose their im-
permeability in the course of years when kept in dry air. With
the loss of this quality the seed is not necessarily deprived of
its power of retaining its vitality for a longer period, since
typically permeable seeds, as has been already remarked, may
preserve their germinative capacities for many years. It, how-
ever, is deprived of the power of prolonging its existence in the
soil ; and in consequence it either germinates or dies. How
long a seed with impermeable coverings could remain alive
when buried deeply in the soil, it would be extremely difficult
to determine with accuracy. But it is apparent from Professor
Ewart's own observations that under the conditions of undis-
turbed primeval forest in Australia they might lie buried in the
64 STUDIES IN SEEDS AND FRUITS
soil for very long periods without losing their impermeability.
Under such conditions he found that all Acacia seeds found
below the surface possessed impermeable coats and required
special treatment to produce swelling and germination.
Whether or not the seeds always retain their vitality when
they preserve their impermeability is another matter, since
longevity, as Professor Ewart observes, may not depend
primarily on the impermeability of the seed-coats, but on a
peculiar inherent property of the protoplasm, the duration of
which under the soil is secured by the impermeable coverings.
Seed- Seed-longevity would seem therefore to be determined by two
termined by independent eventualities, the limit of the impermeability of
the imper f t^e coats and the limit of the staying power of the protoplasm
meabihty of o f the kernel or embryo ; and the question arises as to which
the coats and J i r -r* r T->
by the limit lasts the longest. Amongst the results or Professor rLwart s
ing power of experiments it is easy to find cases where impermeability has sur-
the embryo. v i vec j its utility ; but it would be hazardous to assert that this is
the usual course of events under the soil. This method of stat-
ing the problem seems to be the best way of reconciling the views
of Mr Crocker in America and Professor Ewart in Australia.
An important outcome of these two series of investigations
is that the issues can be narrowed, thus permitting one to dis-
tinguish between the extrinsic and the intrinsic in the results
of experiments. Results applicable to the behaviour of the
seed in air are in a sense extrinsic, since such are not the usual
conditions under which Nature tests its longevity. Those that
can be brought into some kind of relation with the seed as it
occurs naturally in the soil are likely to be the most instructive.
Two questions, it would seem, have shaped themselves whilst
considering these results.
The two The first is : Under which conditions would an imper-
raised by the meable seed retain its vitality longest, in the air or in the soil ?
tionsfof Mr The second is : Which has the greatest staying power, the
Crocker and impermeability of the seed-coats, or the germinative capacity
of the kernel ? Notwithstanding the evidence before us, the
answer to both of them is indeterminate.
THE IMPERMEABILITY OF SEEDS 65
There are, however, one or two points to which further
reference might be made. Thus, to take the first query, it
may be replied that even in the case of the most impermeable
seeds the effect of being kept in the dry air of a room for
many years would be undoubtedly to favour the development
of small cracks in the outer covering, thus converting them by
degrees into permeable seeds. My observations on the seeds
of Entada scandens (Chapter X) will go to show how this could
be brought about. We can thus perceive how much less
likely it is that impermeable seeds exposed without protection
to the weather could withstand year after year the alternating
conditions of heat and cold, of sun and shade, of drought and
humidity, which in one form or another they would experience
whatever their situation. In an elaborate series of experiments,
in which he reproduced the extreme changes between moist and
dry conditions and between heat and cold in various shapes,
such as an ordinary climate would present, Dr Gola found that
the seeds lost their impermeability. To come to a matter of
my own observation, it is doubtful whether any of the
numerous impermeable seeds washed up on tropical beaches
could withstand for many years exposure to the sun and rain.
All of them would show sooner or later signs of wear and tear
in the injuries to the outer coats.
On the other hand, buried in the soil, the seed would be
more or less safeguarded against the risks to which a seed
lying on the ground would be exposed. But the degree of
protection would vary with the depth below the surface, so
that the seed deepest down, as shown by Duvel, Crocker, and
Ewart, would have the longer life. At the same time new
dangers might arise ; but on the whole it seems likely that
under such favouring conditions as characterise the typical
Australian forests, the buried seed might retain its imper-
meability for much longer periods than when kept dry in
cupboards or in botanical museums.
But this raises again the second question whether the
germinative capacity would be similarly retained. Of this it
5
66
STUDIES IN SEEDS AND FRUITS
The little
value of
negative
evidence.
The seat of
impermea-
bility.
may be said that we shall probably be never quite secure in our
interpretation of Nature's experiments in this direction. But
this insecurity does not invalidate the testimony altogether ;
and it scarcely seems prudent to ignore altogether the accumu-
lation of evidence respecting the high antiquity of "germinable "
seeds found in ancient graves or when an old soil is disturbed.
With regard to the little value of negative evidence in
such an inquiry, I point out in the next chapter that we can
never be certain that the failure is due to the incapacity of
the germinative powers and not to the method employed.
Both Crocker and Ewart are emphatic on the point that it
would require more evidence than was deemed necessary by
the earlier investigators to convince us that the cause of the
failure to respond by germination to the call of their experi-
ments lay always with the seeds. I venture to think, and
here I am supported by a considerable amount of evidence
given in the succeeding chapters, that the truest test of the
potential vitality of an impermeable seed is to be found in
the constancy of its weight under all ordinary conditions and
under the influence of time. If a seed with sound coats
gained nothing in weight after weeks of immersion in water,
made no response to the varying hygrometric changes of the
atmosphere, and preserved the same weight for a number of
years, I would presume its germinative soundness, whatever its
previous history or whatever its attested antiquity.
Not the least important part of Professor Ewart's memoir
is the account given by Miss White in an appendix of the
results of her investigation of the structure of coats of imper-
meable seeds. After making a microscopical examination of
the coats of nearly seventy species of impermeable seeds which
had been the subject of Professor Ewart's inquiry, she formed
the following conclusion : " As a general rule in small and
medium-sized seeds the cuticle is well developed, and repre-
sents the impermeable part of the seed-coat ; whilst in the case
of large seeds, such as those of Adamonia Gregorii, Mucuna
gigantea^ Wistaria Maideniana^ and Guilandina bonducella^ the
THE IMPERMEABILITY OF SEEDS 67
cuticle is extremely unimportant and inconspicuous. In these
seeds the extreme resistance which they exhibit appears to be
located in the palisade cells.". . . The circumstance that the
seat of the chief resistance to the penetration of water may lie
in large seeds in the deeper tissues may explain how Dr Gola
comes to consider that this is the rule for impermeable seeds.
Miss White's investigations, however, establish the fact that
the seat of impermeability lies for most seeds in the structure-
less cuticle, a conclusion previously indicated, but on less
extended grounds, by the inquiries of Nobbe and by those of
Bergtheil and Day.
SUMMARY
(1) The frequency of impermeability in seeds of certain families,
especially of the Leguminosae, which was first indicated by Nobbe a
generation ago, has within the last few years been established by Gola,
an Italian investigator. His results bring out the facts that, though
more typical of some genera than of others, impermeability is not a
generic character, and that it is rarely even a specific character, since
both permeable and impermeable seeds are commonly found in the
same species (p. 57).
(2) Another of the inferences of Nobbe that delayed germination is
due in many cases to the impermeability of the seed-coverings to water
has been confirmed and extended by the recent researches of Crocker
in America. After this point, questions affecting seed-impermeability
usually resolve themselves into matters concerning seed-longevity.
Crocker rejects the idea that a seed's long life is as a rule to be
attributed to embryo characters or to the dormancy of protoplasm
(p. 60).
(3) However, Ewart in Australia, after very extensive researches,
arrived at the conclusion that the longevity of seeds depends not on
their coverings, but on the persistence of the protoplasmic constitution
of the embryo or kernel ; and he views impermeability of the coats as
an adaptation for ensuring the long life of the seed under soil-conditions
(p. 61).
(4) Of the 2500 species (more or less) with which Ewart deals, either
directly or through the observations of others, rather less than i per
cent, are long-lived seeds that will retain their germinative capacity
from fifteen to one hundred years and over. Of these " macrobiotic "
68 STUDIES IN SEEDS AND FRUITS
seeds all possess more or less impermeable coats, and three-fourths are
leguminous (p. 62).
(5) It is suggested in this chapter that seed-longevity should be
regarded as determined by two factors, represented in the imper-
meability of the coats and in the persistence of the protoplasmic
constitution of the embryo-kernel (p. 63).
(6) It is also suggested that, accepting impermeability as an adaptation
to soil-conditions, we should leave to the future investigator these two
points to determine : (a] whether the impermeable seed would retain its
germinative capacity longer in the soil than in the air ; (b] as to the
relative durability of the impermeability of the seed-coats and the
germinative capacity (p. 64).
(7) Recent investigators lay stress on the fact that negative results
obtained by earlier investigators in testing the persistence of the
germinative powers of hard seeds were more probably due to their
inacquaintance with the right methods of procuring germination than
to failure on the part of the seeds (p. 66).
(8) Whilst considering that a combination of the theories of Crocker
and Ewart would present the best working hypothesis, the author is
inclined to the view that the most practical tests of the potential
vitality of an impermeable seed are to be found in the constancy of its
weight under all ordinary conditions and in the lapse of years. He
would presume the germinative capacity of such a seed, whatever its
antiquity, provided, as has just been implied, that its coats are sound,
that it absorbs no water, and that it makes no response by alterations
in its weight to the varying hygrometric states of the air. The author
also does not regard it as prudent to ignore altogether the accumulation
of evidence respecting the great age of " germinable " seeds found in
ancient graves or when an old soil is disturbed (p. 66).
(9) Lastly, the opinion of Nobbe and of later investigators that the
seat of impermeability lies in the outer coverings of the seed has been
confirmed by the results of the recent researches of Miss J. White,
who places it in the case of small seeds in the cuticle and with large
seeds often in the outer palisade cells (p. 66).
CHAPTER IV
PERMEABLE AND IMPERMEABLE SEEDS
THE observations and experiments on the results of which
the four following chapters are based cover the period of
1 906 to 1911. They were practically completed, and the
greater part of the results elaborated and written out, before
the works of other investigators had been consulted. In this
condition they have been in the main reproduced in these
pages, as I thought it best that they should tell their own
story, my original purpose having been to make an in-
dependent study of the impermeability of seeds without
being influenced by the ideas of others. That has been
done ; but in the final summing up of my own results 1
have been guided in the estimate of their value and in the
drawing of my conclusions by the results obtained and the
opinions formed by other inquirers.
In order to introduce the subject and to give method to Comparison
the arrangement of the results of a large number of observa- fGuilandina
tions and experiments, I will take the very divergent behaviour, and d Cana*
as revealed by the balance, of the seeds of two leguminous vaiiaensi-
plants, Guilandina bonducella and Canavalia ensiformis. The
first named has a very hard grey seed of the size and form
of a marble, weighing usually about 40 grains, and possessing
very thick coats. The second has a thin-skinned white seed,
about 20 millimetres long, weighing 20 to 25 grains, and
typical of a large number of leguminous plants. (See Note
5 of the Appendix.)
6 9
yo STUDIES IN SEEDS AND FRUITS
(a) as re- On placing these two seeds in water we obtain very
permeability, different results. That of Guilandina bonducella absorbs no
water and preserves its original weight after an immersion
of many months or even years. On the other hand, the
seed of Canavalia ensiformis begins to swell in a few hours,
and within twenty-four hours has doubled its weight. One
seed, therefore, is impermeable or waterproof, whilst the
other is permeable. But this difference in behaviour is
associated with a difference in other qualities. If we
weigh the seeds daily for a week or two, employing a
quartz pebble as a standard of comparison, we observe
that the seed of Guilandina bonducella behaves exactly like
the pebble and keeps its weight to within a small fraction
of a grain. The seed of Canavalia ensiformis, on the con-
trary, varies considerably in response to the daily changes
in the atmospheric humidity, the amplitude of its variations
amounting to 2 or 3 per cent, of its average weight. One
seed, therefore, behaves hygroscopically, and the other does
not. As might have been expected, it is the impermeable
seed of Guilandina bonducella that is non-hygroscopic, whilst
with the seed of Canavalia ensiformis permeability and
hygroscopicity go together. When extending the weighing
observations over twelve months, we find the same features
of difference displayed. Whilst the Guilandina seed maintains
its weight unchanged, the Canavalia seed continues to exhibit
the same hygroscopic variations. If we were to represent
these results in a diagram, we should denote the behaviour of
the seed of Canavalia ensiformis and that of the Guilandina
seed by a horizontal line. The line of the last named
would be even, but that of the Canavalia seed would
display numerous zig-zag irregularities, marking the hygro-
scopic responses of the seed. It is essential to understand
that we are here dealing with seeds that have completed
their spontaneous drying in air. Where the shrinking
and drying process is unfinished quite other influences
come into play.
Up to this point we have been dealing with the seed in
its coats. But if we remove these coverings we find another
singular contrast in the behaviour of these, two seeds. In
the instance of Canavalia ensiformis we discover that it makes
no essential difference whether we employ the seed in its
coverings, or puncture it through its coats, or deprive it of
them altogether. In any case the same average weight is
maintained, the baring of the kernel or puncturing of the
coats merely resulting in a small increase of the hygroscopic
range. Whatever may be the function of the coats of a
permeable seed, they do not prevent it from responding from
day to day to the variations in the atmospheric humidity,
though they may regulate the process. This would seem
to be true of the large majority of similar seeds, and it
follows naturally from the permeable character and the
hygrometric behaviour of the seed-coverings. (See Note 6
of the Appendix.)
In the table below I have given the results of simultaneous
observations on the bared, punctured, and entire seeds of
Canavalia ensiformis collected from the plant at the same time.
The table explains itself, except that one may add that the
hygroscopic or hygrometric variation is the range of the
changes in weight exhibited in the course of two or three
weeks stated as a percentage of the total weight.
COMPARISON OF THE BEHAVIOUR OF THE SEEDS OF CANAVALIA
ENSIFORMIS WHEN BARED, PUNCTURED, AND ENTIRE.
The influence
of the seed-
coats on the
changes in
the seed's
weight,
(a) in the
case of a
permeable
seed,
Condition of seed.
Hygroscopic
variation.
Loss of weight in
two years.
Entire in its coats ....
Punctured through its coats
Bared of its coats ....
2 '5 per cent.
3'
4 '0-4 '5 per cent.
Nil.
>
i)
If we repeat these experiments with the seeds of Guilandma (b) in the
bonducella^ and either remove the hard, impermeable, shell-like impermeable
coats or pierce them with a file, we obtain results of quite a seed -
7 2
STUDIES IN SEEDS AND FRUITS
The dis-
closure of
the ultra-
dryness of
impermeable
seeds.
different nature. A sample of the bared kernels weighing
100 grains immediately after the removal of their shells
will be found after a period of four or five days to have
increased its weight to in or 112 grains. The gain in
weight begins as soon as the hard coats are removed ; and
thus my materials became sensibly heavier whilst in prepara-
tion for the balance. In one case, for instance, a sample
of 500 grains weighed 503 grains after an hour occupied
in preparing it for an experiment. This increase in weight
is maintained, although in a diminished degree, for a long
period. In fact, the bared kernel never returns to the
weight it possessed when enclosed in its impermeable cover-
ings. As is shown in the table below, after a period of a
year and more, it is still 3 or 4 per cent, in excess of its
original weight.
RESULTS OF THE EXPOSURE TO AIR OF THE BARED KERNELS OF
GUILANDINA BONDUCELLA. (WEIGHT IN GRAINS OF six KERNELS
AT VARIOUS PERIODS.)
Immedi-
ately after
being bared
of their
After
5 days.
After
zo days.
After
3
months.
After
6
months.
After
16
months.
After
zo
months.
After
z6
months.
shells.
100
113-4
1 1 I'D
107-3
xoy'o
103-0
103-3
104-4
The explanation, of course, is simple. The kernel when
bared, being in a state of ultra-dryness, supplies its deficiency
by absorbing water from the air. In so doing it has changed
its nature and now responds to the hygrometric variations
of the weather, behaving in fact like the kernel of a permeable
seed. We have here, then, the disclosure of another striking
character distinguishing impermeable seeds, such as those of
Guilandina bonducella^ from permeable seeds, like those of
Canava/ia ensiformis.
This curious quality has been exhibited in varying degrees
PERMEABLE AND IMPERMEABLE SEEDS 73
by the bared kernels of nearly all impermeable seeds that have
been subjected to this test. The dry friable kernels when
coarsely broken up contrast greatly in their appearance with
the relatively moist and compact materials of permeable
seeds ; and hence it could be presumed without further
inquiry that absorption of water-vapour from the air is the
cause of the subsequent increase in weight. But this capacity
in seeds of becoming considerably heavier when exposed to
the air than when locked up in their impermeable coats
pre-supposes a condition of ultra-dryness within the seed
itself. We should thus expect that the seeds of Gullandina
bonducella, as types of impermeable seeds, would contain
much less water than typical permeable seeds, such as those
of Canavalia ensiformis.
We have accordingly to appeal to the evidence of the oven An appeal to
in order to interpret the indications of the balance ; and in the O f the oven,
table now to be given are to be found the results of exposing
these two kinds of seeds to a temperature of 100 to 105 C.
for a period of from one and a half to two hours.
WATER-CONTENTS OF A TYPICAL PERMEABLE AND A TYPICAL IM-
PERMEABLE LEGUMINOUS SEED AS ASCERTAINED BY EXPOSURE TO
A TEMPERATURE OF 100 TO 105 C. FOR i^ TO 2 HOURS.
Character
of seed.
Number of
experiments.
Average
water-
contents.
Range of result.
Canavalia ensiformis
Permeable
4
1 6 per cent.
14 to 1 8 percent.
Guilandina bonducella .
Impermeable
5
8
6 to 10 ,,
Note. These results represent the combined water-contents of kernel and coats,
have omitted decimal fractional parts, as these values are dealt with in later chapters.
These results establish the ultra-dryness of the seed of
Guilandina bonducella enclosed in its impermeable coverings ;
and we recognise in the absorption of water-vapour from the
air by the bared seed an attempt to assume the condition of a
permeable seed. As far as their water-contents are concerned,
74 STUDIES IN SEEDS AND FRUITS
permeable hygroscopic seeds are, relatively speaking, in a
state of saturation, or perhaps it would be more correct to
say in a state of equilibrium, with regard to the moisture
of the air. On the other hand, impermeable seeds like
those of Guilandina bonducella stand in no such relation to
the atmosphere, and preserve their abnormally dry condi-
tion independently of any atmospheric changes. When, by
the removal of their coverings, such seeds have been
deprived of their power of resisting the permeation of
water, either as vapour or as liquid, they rapidly supply
their deficiency by absorbing it from the air. Roughly
speaking, the amount of water regained from the air
by the bared seed of Guilandina bonducella represents the
deficiency in its water-contents, as compared with the bared
seed of Canavalia ensiformis, or, in other words, the price
of its impermeability.
As regards their water-contents and other characters
diagnostic of permeable seeds, the seeds of Canavalia ensiformis
may be placed with our edible leguminous seeds, such as Peas,
Broad Beans, Scarlet-runners (Pisum sativum, Faba vu/garis y
Phaseolus multiflorus), which usually contain 15 or 16 per cent,
of water. But the low percentage of water in the seeds of
Guilandina bonducella appears quite abnormal when compared
with the data given in the ordinary tables of the analyses
of seeds used as food, though representative of impermeable
seeds. Rice, Maize, Wheat, and other cereal grains, for
the most part permeable, contain from 12 to 15 per cent,
of water, whilst the flour yielded by them holds 1 1 or
12 per cent.
Up to this point the indications appear to be sufficiently
plain, though the subject gives promise of much complexity.
But now comes another curious fact. Whilst the coats of a
permeable seed like that of Canavalia ensiformis behave hygro-
scopically when removed from the seed, neither increasing nor
decreasing their previous average weight, it is very different
with the impermeable seed.
PERMEABLE AND IMPERMEABLE SEEDS 75
The detached shell-like coverings of the seed of Guilandina
bonducella possess the same quality. of ultra-dryness and display
the same absorptive capacity in air as the bared kernel, though
to a less degree. They exhibit the relation between the water-
contents which we might have expected, the larger water-per-
centage of the seed-coverings being associated with a smaller
absorptive capacity in the air as compared with the kernel.
These qualities are well brought out in the tabulated results
given below of an experiment in Grenada in which the shell
and the kernel of several seeds were equally divided in each
case between two samples, so that the air exposure and oven-
tests were applied to truly mixed samples. It may here be
added that, as in the case of the kernels, the detached shell re-
tains its excess for a long period, though in a diminishing ratio.
In one experiment, after a lapse of twenty-one months it still
weighed 6 per cent, heavier than when first removed.
COMPARISON OF THE ABSORPTIVE CAPACITIES IN AIR WITH THE WATER-
CONTENTS OF FRESHLY BARED KERNELS AND OF THE DETACHED
SEED-SHELLS OR COVERINGS OF GUILANDINA BONDUCELLA, THE
SAMPLES BEING TRULY MIXED, AS ABOVE DESCRIBED.
The shell or
covering of
the seed of
Guilandina
bonducella
has the same
quality of
ultra-dryness
and the same
absorptive
capacity as
the kernel.
Gain in weight
after exposure to the
air for 4 days.
Original water-
contents as determined
in the oven.
Seed-shells .
Kernels
iz'o per cent.
16-2
7 '6 per cent.
O ,,
We are thus brought face to face with the curious cir-
cumstance that if we break open one of the seeds of
Guilandina bonducella and allow it to remain in this condition
for a few days it will increase its weight on the average
by 1 1 or 12 per cent. It is essential to break through the
seed-shell, it being immaterial whether the shell is in a few
or in many pieces, or whether the kernel is left whole or
in fragments.
The same
result is pro-
duced bjr
puncturing
or filing the
seed-coats.
76 STUDIES IN SEEDS AND FRUITS
The same effect is produced by puncturing or filing through
the shell, though, as shown in the results tabulated below, the
change is much more gradual. Here the total increase of
weight is the result of the combined absorptive capacities of
the kernel and its coverings.
RESULTS OF FILING INTO THE SHELL OR HARD COVERING OF THE
SEEDS OF GUILANDINA BONDUCELLA, STATED AS A PERCENTAGE OF
THE ORIGINAL WEIGHT OF THE SEEDS (34 TO 35 GRAINS).
in
.
Ul
</>
"c3 ^
N CO
J2
J3
i
6
^
-fl
x
'&">
K *
~ I)
II
j
G
o
"c
O
"o
i
"<u
o
g
S
e
S
e
s
O *^
^
^
H<N
m
vo
oo
M
^
*
""
M
H
N
N
*A seed with
lOO'O
xoo'o
lOO'O
lOO'O
lOO'O
100*0
lOO'O
100*0
lOO'O
lOO'O
shell intact
fA seed filed
XOO'O
105-8
108-2
108-5
no'4
106*6
106*9
108-3
io8'o
107*2
halfthrough
its shell
fA seed with
lOO'O
106-9
109-1
109*2
III'O
107*0
I0 7'3
108-8
108*5
107-8
kernel ex-
posed by
filing
* The seed with shell intact, weighing originally 35-06 grains, varied only between
35-04 and 35 "08 grains during the period.
t After the experiment both germinated readily in 4 to 5 days, and produced healthy
plants.
By comparing the changes which these seeds experienced
in the first three or four months we find :
(a) That the seed with shell intact varied only at the rate
of 10 1 00 of its weight during these twenty-four
months, a result probably instrumental and too small
to be noted in the table ;
() That the seed with shell filed halfway through gained
1 0*4 per cent, in weight ;
(c) That the seed with its kernel exposed by filing through
into the seed-cavity gained 1 1 per cent.
I shall have to return again to this subject when further
discussing these matters in Chapter VI ; but some additional
remarks may here be made.
PERMEABLE AND IMPERMEABLE SEEDS 77
In the first place, the only impervious portion of the seed-
shell is the outer skin and the hardened tissue immediately
beneath it, but little effect being produced by merely filing the
cuticle. If we file through this outer impervious portion, it
makes but little difference in the subsequent behaviour of the
seed whether we expose the kernel or file only half through
the shell.
In the next place, it should be noted that whilst the
freshly bared seed gains its maximum weight by imbib-
ing moisture from the air in a few days, the filed seeds
occupy some months in reaching their greatest weight.
They then remain at about the same average weight and
behave like permeable seeds in their response to the hygro-
metric variations of the atmosphere. But the most note-
worthy feature in the behaviour of these filed seeds is that
they retain their germinative capacity after two years in
this condition.
In the third place, the behaviour of the filed impermeable
seeds of Guilandina bonducella may be contrasted with that
of the permeable seeds of Canavalia ensiformis, where, as
before described, the effect of puncturing the seed-cover-
ings is merely to increase to some degree the hygroscopic
variation.
Such, then, is the contrast in the behaviour between
permeable and impermeable seeds as described in the case
of two type seeds in the previous pages. The principal
differences are there outlined to a sufficient extent for this
introductory notice of my observations on this subject.
But there still remain some interesting features in the
absorptive capacity of impermeable seeds to be noticed and
some general reflections to be made before this chapter is
brought to a close.
An accident led me to the discovery of another singular
quality of impermeable seeds, one that probably could have
been foreseen, had the successive stages of this inquiry followed
the order adopted in this chapter. However, it was this
Exposure to
a tempera-
ture of 100
C. does not
prevent a
bared imper-
meable seed
from increas-
ing its
original
weight by
absorbing
water-
vapour from
the air.
Both the
kernel and
the coats of
an imper-
meable seed
retain their
absorptive
capacities in
air after ex-
posure to a
temperature
of 100 C.
7 8 STUDIES IN SEEDS AND FRUITS
accident that first disclosed to me the ultra-dryness of imper-
meable seeds. After weighing a sample of kernels of Guilan-
dina bonducella which had just been exposed in the oven for a
short time to a high temperature and had lost 8 per cent, of
its weight, I unwittingly left it over-night in the pan of the
balance, and was surprised to find that it was between i and 2
per cent, heavier than before it was placed in the oven. During
the night it had regained all the water driven off by heat and
something more.
The results of numerous oven-experiments on this and
other impermeable seeds go to make it evident that the
capacity of such a seed to considerably increase its weight
when exposed in a broken condition to the air is but little
affected by first subjecting the material to a temperature
of 1 00 to 105 C. for an hour or two. If, to take an
actual case, a seed on being broken up increased its weight
after three or four days' ordinary exposure on my table
from 100 to 113 grains, it made but little ultimate differ-
ence whether or not its weight had first been reduced
to 93 grains through the loss of water in the oven. I
will here appeal again to the behaviour of the seeds of
Guilandina bonducella^ reserving for a subsequent chapter the
detailed treatment of this matter as regards other imper-
meable seeds.
There are given below the results of two actual experi-
ments, the first in Jamaica and the second in Grenada, on the
effect of exposure to a temperature of 100 to 105 C. on the
absorptive capacity in air of the broken seeds of this plant.
In the second experiment the seed-coats were separated from
the kernels, thus enabling one to differentiate between the
bared seed and its coverings in this respect. Since the
seeds in this case were equally divided between the samples,
we are able to compare the absorptive behaviour in air of
truly mixed materials under these different conditions. We
thus perceive that in the slight influence of exposure to
high temperatures on their absorptive capacities both the
PERMEABLE AND IMPERMEABLE SEEDS 79
kernel and its coverings behave in a similar manner. (For
convenience I have also added under C the average result
of all my experiments.)
EFFECT ON THE ABSORPTIVE CAPACITY IN AIR OF EXPOSURE TO A
TEMPERATURE OF 100 TO 105 C. FOR i TO 2 HOURS IN THE
CASE OF BROKEN SEEDS OF GUILANDINA BONDUCELLA. (Results
stated in percentages.)
1
A.
Three broken
125 grains.
seeds, kernels and coats mixed together, originally weighing
Original weight.
Weight after the
oven test.
Subsequent weight after
four days in air.
IOO
93 -6
"S'3
/
B<
V
Seed-coats and kernels treated separately, the true mixing
being secured by dividing the seeds between them. Three
1 06 grains were used.
of the samples
seeds weighing
Materials.
Condition of experiment.
Subsequent
weight after
four days in air.
Coats
Kernels .
)>
loo Reduced to 92*4 after exposure
in oven to 100-105 C-
100 Not heated
too Reduced to 95-8 after exposure
in oven to 100-105 C.
100 Not heated
"3'3
II2'0
II5-5
Il6'2
C ,
\
Average results of all experiments on the absorptive capacity in air with and
without previous exposure to a temperature of 100-105 ** m tne case f l ^ e
kernel and coats together.
Original wek
[ht.
Absorptive capacity in air.
Average of eleven
experiments without
heat.
Average of five experiments
with previous exposure
in oven.
IOO
111-5
na'o
8o
STUDIES IN SEEDS AND FRUITS
An imper-
meable seed's
capacity of
absorbing
moisture
from the air
in the broken
state varies
inversely
with the
water-
contents.
The be-
haviour of
the perme-
able seed
under the
oven test
That the absorptive capacity of the impermeable seed, that
is to say, its power of absorbing water from the air in the
broken condition, varies inversely with the water-contents was
implied a few pages back. A small water-percentage and a
large absorptive capacity go together, and vice versd. This is
brought out in the tabulated results given below for Guilandina
bonducella. These experiments were carried out in different
places and under varying hygrometric conditions, so that only
a general result is to be expected. Better examples of the
principle that the impermeable seed when broken up takes up
water from the air in proportion to its ultra-dryness are given
in Chapter VI.
RESULTS OF THREE EXPERIMENTS ON THE SEEDS OF GUILANDINA
BONDUCELLA, SHOWING THAT WITH IMPERMEABLE SEEDS THE SEED
WHICH ADDS MOST TO ITS WEIGHT IN THE BROKEN CONDITION
BY ABSORBING WATER-VAPOUR FROM THE AlR IS THE SEED WITH
THE SMALLEST WATER-CONTENTS. (Stated in percentages, the samples
varying between 50 and 130 grains.)
Original
weight.
Reduced weight
in oven.
Water-
percentage.
Subsequent weight
after exposure to air
for four days.
IOO
IOO
IOO
89*9
93*6
6*2
6-4
105*2
114*2
115-3
When we contrast the behaviour under the oven test of a
permeable and an impermeable seed we obtain very different
results. The seed of Canavalia ensiformis, after being subjected
to the same oven test in the broken state, regains in a few
days most of its lost water from the air ; and after a week or
two reaches its original weight affected only by the ordinary
hygroscopic variation of 2 or 3 per cent. For example, a
sample of seeds weighing 100 grains would be reduced in the
oven to about 85 grains. After standing for four or five days
its weight would be about 98 grains, and in a few more days
it would attain its original weight, varying according to the
PERMEABLE AND IMPERMEABLE SEEDS 81
hygrometric condition of the atmosphere between 99 and 101
grains.
Enough has been said in this connection of the singular
ultra-dryness of impermeable seeds. Though illustrated here
only by the seeds of Guilandina bonducella^ this capacity is
described in the case of several other impermeable seeds in
Chapter VI. This quality depends for its maintenance entirely
on the impervious character of the outer part of the seed-
coverings. There is nothing impermeable in this seed but the Ultra-dry-
skin and the portion of the layer immediately beneath it. Let tainedbythe
it be pierced only by a pin-prick, and sooner or later the seed S^oV the
takes up water from the air and ultimately behaves like a seed-coats
ifi j j i- i M i i andassoci-
permeable seed, soon decaying as it lies in the soil, unless the ated with a
conditions for germination arise. Let, however, the outer
covering remain intact, and the embryo within may remain for
long periods in a state of suspended vitality. But the imper- kernel,
meability of the coverings is not the only conspicuous quality
associated with ultra-dryness. We have already seen that in
the case of the seed of Guilandina bonducella, although both the
coverings and the kernel share this character, it is to the kernel
that it more especially belongs. In the sample examined,
whilst the water-contents of the seed-coverings amounted to
7-6 per cent., in the kernel they were only 4/2 per cent. In
Chapter VI it will be shown that this excess of water in the
seed-coats as compared with the kernel is a typical character
of impermeable seeds, a character that distinguishes them from
permeable seeds of the same order, the coats of which as a rule
possess a rather smaller water-percentage than the kernel.
It is to be doubted if any seeds are better fitted to preserve
their germinating power for ages when buried in dry soil than
the seeds of Guilandina bonducella. Professor Ewart, who
employs the synonym of Ctesalpinia bonducella for this seed,
places it amongst his group of " macrobiotic " seeds that would
last from fifteen to over a hundred years under favourable con-
ditions. I fancy that some very old seeds were once tested at
Kew, but cannot put my finger on the reference. However,
6
82 STUDIES IN SEEDS AND FRUITS
Professor Ewart gives the result of an experiment where, out
of twenty-four seeds fifteen years old, five germinated. I only
tested their keeping capacity in the case of two seeds collected
by me ten and eleven years previously in Fiji, and found that
both germinated readily and produced healthy plants.
Negative Negative results in the germination of old impermeable
beTexclusive- seeds should not be exclusively relied upon, since they may
in testin the ar * se more f rom a failure in the conditions of the experiment
longevity of than from a failure in the seed. For instance, it is not at all
impermeable -11 ... ... .
seeds. easy, one might almost say it is impossible, to exactly repro-
duce the processes of nature in a soil-experiment. The initial
step, when we place in warm, moist conditions an impermeable
seed that has been lying dry for years in the air of a room is a
distinct departure from the natural process ; and, as Professor
Ewart shows in the case of an experiment on " fifty-year " old
seeds under what he describes as " optimal " conditions, there
may be no results. Yet if the seeds that still remain intact
and impermeable after such a soil-experiment are placed in a
germination chamber, after the impermeable cuticle has been
removed by sand-papering, about half on the average will ger-
minate. In such a case every seed having been made permeable
must either germinate or die. But we are not, I venture to
think, justified in presuming that the seeds which failed to
germinate in the second experiment had necessarily lost their
vitality. The inference we should be apt to draw from the first
soil-experiment that the seeds had lost their germinative powers
would be disproved, as Professor Ewart observes in recounting
the experiments, by the test in the germinating chamber ; and
it is equally possible that our second inference might be
erroneous if we assumed that the failures in the germinating
chamber are all to be attributed to the lost powers of the seed
and not to some failure in the conditions.
Artificial methods, such as sand-papering, filing, scraping,
the use of an acid, etc., are generally necessary in experiments
to procure the germination of impermeable seeds, the seed
being rendered permeable by being deprived of its cuticle ;
PERMEABLE AND IMPERMEABLE SEEDS 83
but in my own experiments, where scraping or filing was
generally adopted, I attached but little importance to the
occasional negative results. Every seed of average weight
that possessed completely sound coverings, that displayed no
increase in weight whilst immersed in water for weeks, and
that behaved like a quartz-pebble in response to the hygro-
metric changes of the air, was for me a germinable seed,
whatever its age. An ineffectual result I regarded as merely
reflecting on my method, provided that the seed originally
possessed the qualities named.
The final proof seems to me to lie almost outside the
reach of the direct experimental method. Nature would
probably follow a very slow and graduated process in pro- Suggested
curing the germination of ancient seeds ; and it is not easy longevity in
to see how we are to imitate such a process, and yet be theduration
confident that our failures lie in the seeds and not in the ternal
conditions of our experiment. In default of this there is impermeable
still open to us the plan of testing the duration of the three seeds -
chief qualities of an impermeable seed : the soundness of the
coats, the impervious character of its outer covering, and its
practically non-hygroscopic behaviour. The indirect method
would appear to give most promise in the investigation of
the longevity of impermeable seeds.
Yet occasionally some strain of weakness due to a defect
in the shrinking process offers to the opposing external condi-
tions their opportunity, and the seed that appeared able to
survive for very long periods begins to fail. The indications
of the change are exceedingly interesting. They have already
been noticed on p. 76 in this chapter in the description
of the results of filing into seeds of Guilandina bonducella^ and
they will be again noticed in the account of a similar ex-
periment on the seeds of Entada scandens in Chapter VI.
During several months the filed seeds gradually increased in
weight, until, in the case of the first-named, they had increased
by 10 or n per cent., and in that of Entada scandens 2 or 3
per cent., assuming ultimately the condition of permeable
84 STUDIES IN SEEDS AND FRUITS
seeds and behaving hygroscopically. Such is the change that
impermeable seeds undergo in the air when their coats are
injured ; but this is the natural end of all such seeds in the
soil. It is the loss of their impermeability, according to
Professor Ewart, that brings the resting life of Acacia seeds
in the surface -soil of the Australian forests to a close,
leaving no choice between germination and death. The
earlier seeds to swell in his experiments were, as he observes,
mostly dead.
Similar indications were at times presented in my long
weighing experiments on impermeable seeds. In Chapter X,
which is devoted to the fate of seeds as indicated by the
balance, I refer to the gradual increase of weight, extending
over a year or more, of seeds of Entada scandens and Guilandina
bonducella that displayed slight defects in their coats.
One may perhaps be permitted to slacken for a while the
reins that control the fancy whilst reflecting on the mysterious
The ultra- development of this condition of ultra-dryness in impermeable
mlablefseed seeds in association with the completely suspended vitality of
and its t ^ e em bryo. If, when we come to discuss this subject in its
cosmic sug- J * .
gestiveness. general bearings in a later chapter, it loses a little of its
mystery, we shall still, I venture to think, regard the im-
permeable seed as one of Nature's indications of the direction
in which speculation should be aimed in discussing the extra-
terrestrial or cosmic aspects of plant-life. If such a seed as
is presented to us now will not withstand the strain of the
ages, it suggests to us in more ways than one the type of
plant-organism that might withstand the test. It seems to
show us how a plant in a state of suspended vitality might
tide over great periods of time not only on this planet, but
on others where different conditions prevail.
Such a seed appears to be almost unconditioned when
contrasted with a permeable seed, which is very much in
touch, with its surroundings, and responds closely in its
changes of weight to the varying hygrometric states of the
atmosphere. The life of the embryo of a permeable seed
PERMEABLE AND IMPERMEABLE SEEDS 85
depends largely on the conditions in which the seed is placed,
and it is ever threatened by many dangers, against which the
embryo of an impermeable seed is fully protected. It is
immaterial to the young plant enclosed in the hard shell of
a seed of Guilandina bonducella whether the seed lies exposed
to the sun on a desert or is submerged in a swamp. As
compared, then, with the permeable seed, the impermeable seed
seems to present to us a relatively unconditioned existence
of its embryo.
Whilst indulging in such speculations it is pertinent to
ask which was the prior state of the seed, the permeable or Which is the
the impermeable. To this it may be replied that if in past permeable or
ages seeds had no rest-period, the matured seed passing on
at once to germination, the development of the impermeable
state would be of later origin. But the seed-stage may be
conceived as the permanent state of plant-life under certain
iron-bound conditions, such as may prevail on other planets,
and such as may have originally prevailed on the earth. In
such a case the seed-stage would represent the plant's response
to the rigid control of contracted life-conditions, whilst the
vegetative growth would represent in the production of stem
and foliage the plant's response to the expanding conditions
of existence. Lender such circumstances the impermeable
seed would be the older state.
As the plant-world exists at present, though impermeability
has the appearance of necessity, impermeable seeds have to
become permeable in order to germinate. It can, however,
be easily shown, and this will be done in a later chapter, that
in plants possessing both types of seeds the impermeable state
is the goal sought in the seed's development, and that the
permeable seeds have their origin in checks to the shrinking
process. With such plants the impermeable seed, when
beginning to swell for germination, resumes the appearance
of the permeable seed. May it not be that impermeability
is a cosmic character which, in response to the expanding
terrestrial conditions, has largely given place to permeability ?
86 STUDIES IN SEEDS AND FRUITS
It would indeed appear that this is an ancient attribute of
seeds which they are now in process of discarding.
A consideration that gives additional force to this line of
thought is that one of the greatest foes to the development
of impermeability in seeds is mould or mildew. These
minute fungi, when they establish themselves in the tender
skin of the soft, so-called unripe seed, either bring about the
death of the embryo before the resting stage is reached, or
give rise to a resting seed, with permeable coverings, which,
unless conditions favouring germination quickly follow, becomes
at length a shrunken, lifeless seed. (See Note 7 of the
Appendix and Chapter V.) From this standpoint imperme-
ability in seeds might be regarded as a decreasing quantity
in the plant -world, that is, if minute fungi have become
predominant only in the later ages of the earth's life-history.
One could conceive how, as a character of seeds, impermeability
might thus be banished from our planet, and the permeable seed
reign supreme ; and quite in harmony with this conception
would be the indication that Australia, the land of droughts and
the home of the Acacia, offers especially favourable conditions
for the persistence of impermeability in seeds and for securing
their longevity. However, the decision concerning these
views lies with the investigator of the future, and so we will
let the matter rest.
SUMMARY
(1) In order to introduce the subject of the contrast between
permeable and impermeable seeds, I have taken the very divergent
behaviour, as mainly revealed by the balance, of the seeds of two
leguminous plants, that of Canavalia ensiformis as a type of the per-
meable seed, and that of Guilandlna bonducella as a type of the
impermeable seed (p. 69).
(2) Dealing first with the seeds in their coats, the following
differences in their behaviour are described :
(a) The seed of Canavalia ensiformis swells readily in water, and
possesses a stable weight subject to the normal hygroscopic
variation (p. 70).
PERMEABLE AND IMPERMEABLE SEEDS 87
(/>) The seed of Guilandina bonducella absorbs no water after
prolonged immersion, makes no response to the changes in
the hygrometric state of the atmosphere, and retains its
weight unchanged in the course of years (p. 70).
(3) Taking at first the seeds bared of their coats, other contrasts in
behaviour are brought out :
(a) The bared kernel of Canavalia ensiformis preserves its average
weight, but displays a greater hygroscopic variation than in
the case of the kernel protected by the coats (p. 71).
(b] But with Guilandina bonducella^ when the seed is deprived of
its hard, shell-like covering, the kernel gains 1 1 or 12 per
cent, in weight in a few days by abstracting water from the
air. This increase in weight is maintained, but in a diminish-
ing degree, for several months, until stability is reached, when
the weight shows a permanent increase of 3 or 4 per cent.
The ultimate result is that the kernel behaves like that of a
permeable seed (p. 72).
(4) The ultra-dry ness of the kernel of an impermeable seed, which
is thus disclosed, is confirmed by the evidence supplied by the oven
when the seeds are exposed to a temperature of 100 C. It thus
appears that the amount of water regained from the air by the bared
seeds of Guilandina bonducella represents the deficiency in its water-
contents, as compared with the bared seeds of the permeable type
belonging to Canavalia ensiformis (p. 73)-
(5) The next curious feature in impermeable seeds here brought to
light is the fact that the shell-like covering of the seed of Guilandina
bonducella has the same quality of ultra-dryness, though in a somewhat
diminished degree, and the same capacity of supplying this deficiency
by absorbing water from the air, the larger water-percentage of the
shell being associated with a diminished absorptive capacity of the
freshly exposed material. On the other hand, the coats of a seed of
Canavalia ensiformis behave like the kernel, maintaining the same
average weight when removed from the seed, but subject also to
ordinary hygroscopic variation (p. 75).
(6) The same effects are produced by puncturing or filing the
impermeable seeds of Guilandina bonducella^ though the increase in
weight is far more gradual and is extended over months. This
behaviour is contrasted with that of the permeable seeds of Canavalia
ensiformis^ where the effect of puncturing the coats is merely to increase
somewhat the normal hygroscopic variation of the weight (p. 76).
(7) As first accidentally disclosed and subsequently more fully
investigated, it is shown that exposure to a temperature of 100 C.
but slightly affects the capacity of the seeds of Guilandina bonducella
(whether in the case of bared kernels or detached shells) of adding to
88 STUDIES IN SEEDS AND FRUITS
their original weight by taking up water from the air. Of two seeds
broken up and exposed, the one to the ordinary air of a room, the
other at first to a temperature of 100 C., with the resulting loss of
6 or 7 per cent, of its weight, both will ultimately be found after a
lapse of a few days to have acquired a weight on the average II or 12
per cent, in excess of their original weight in the entire condition.
On the other hand, the permeable seed of Canavalia ensiformis displays
quite a different behaviour after being exposed to the oven test. In a
week or two it returns to its original weight, having regained all its
lost water from the air (15 per cent.), and then maintains a stable
weight subject only to the ordinary hygroscopic variation of 2 or 3
per cent. (p. 78).
(8) It is established from the foregoing results that the capacity of
an impermeable seed for absorbing water from the air in the broken
state varies inversely with the amount of the water-contents in the
entire condition (p. 80).
(9) It is indicated by the preceding observations that the ultra-
dryness of the seeds of Guilandina bonducella and of the impermeable
seeds, of which it forms a type, is maintained by the impermeability
of the seed-coats. Though, as compared with permeable seeds, both the
coats and the kernel are ultra-dry, the coats contain more water than
the kernel (p. 81).
(10) It is suggested on a priori grounds that negative germinative
results, even those obtained by investigators with the most modern
means of research, are not to be relied upon as concerning the longevity
of impermeable seeds, provided that the seeds tested are normal in
appearance and in weight and display the normal passivity of seeds of
the type. It is considered that a much safer test is to be found in the
durability of external qualities, all seeds to be regarded as potentially
living or " germinable " that are sound, impermeable, non-hygroscopic,
and of unchanging weight. It is held that the final proof of a seed's
vitality lies almost outside the scope of the direct experimental method
(p. 82).
(n) Yet occasionally, through some defect in its coverings, the
impermeable seed, that appeared at one time as if it could live for ever,
begins to fail. This is shown in the gradual increase of weight extend-
ing over months, as a result of which the impermeable seed assumes the
r6le of a permeable seed. If this occurred under ordinary soil-conditions
the seed would have to choose between germination and death. If it
took place in a seed exposed to the air in a room, the seed might retain
its germinative power for some years, as was indicated in my experi-
ments (p. 83).
(12) A speculative turn is given to the discussion by the reference
made to the " cosmic suggestiveness " of the ultra-dry condition of the
PERMEABLE AND IMPERMEABLE SEEDS 89
impermeable seed. The suggestion is that if the impermeable seed, as
it presents itself in its semi-unconditioned state, cannot withstand for
ever the test of the ages, it supplies us with a hint as to the kind of
plant-organism that might withstand the strain in this and other planets
(p. 84).
(13) The question is put as to which is the original condition,
that of the permeable or of the impermeable seed. In this connection
it is shown that though the impermeable seed has the appearance of
necessity, it has to become permeable in order to germinate, and that
with plants possessing both types of seeds the permeable seed may be
regarded as a seed where the shrinkage has been checked. It is asked
* ' O
whether impermeability may not be a cosmic character, which, in
response to the expanding life-conditions of our particular planet, has
largely given place to permeability (p. 85).
CHAPTER V
THE GROUPING OF SEEDS ACCORDING TO THEIR
PERMEABILITY OR IMPERMEABILITY
HAVING introduced the subject of impermeability in the two
preceding chapters, 1 now proceed to discuss the grouping of
seeds according to the presence or absence of this quality.
We have already seen that impermeable and permeable seeds
are often found in the same plant. This is sufficiently frequent
to be regarded as quite a normal occurrence, the distinction
between the two types being occasionally accentuated by a
conspicuous difference in the external characters, thus enabling
two kinds of seeds to be recognised in a plant. Imper-
meability presents itself in a transition stage in so many plants
that one feels bound to regard it as an attribute that is either
being gradually discarded or being gradually developed ; and
indeed the question whether seeds are now in the act of
acquiring or of dispensing with this quality was the dividing
issue raised at the close of the previous chapter.
It will thus be seen that we cannot divide all seeds between
two groups, permeable and impermeable, since there is a large
intermediate group where the two kinds of seeds are associated.
It is this variable group that will offer some of the best oppor-
tunities of observing the stages in the development or in the
degradation of impermeability, as the case may be. But seeds
belonging to the impermeable group will also be of assistance
in this inquiry, since, although normally impermeable, they
present at times in their defectively shrunken seeds good
materials for study.
90
PERMEABILITY AND CLASSIFICATION 91
As regards the differences in the variable group, it is not
often that the distinction between the two types is con-
spicuously evident to the eye, since similar-looking seeds, as
Professor Ewart remarks, may differ greatly in these qualities.
Usually the differentiation is made in the course of experi-
ments on the capacity of seeds to withstand immersion in water.
However, there are cases, like that of Entada polystachya, where
the two types of seeds are easily distinguished, one small, dark-
coloured, impermeable, and non-hygroscopic, the other large,
light-coloured, permeable, and hygroscopic, and both equally
capable of reproducing the plant. Then again, Mr Crocker, in
the Botanical Gazette for October 1906, has shown that Axyris
amaranthoides has " dimorphic " seeds, the one kind flattened,
winged, permeable, and germinating readily, the other rounded,
relatively impermeable, and only germinating after consider-
able delay. Professor Ewart points out that in the course
of his experiments on more or less impermeable leguminous
seeds, as with the Acacias, these two types of seeds were often
differentiated, the seeds that readily swelled being larger than
the " hard " seeds that required the employment of artificial
means to produce swelling, though both attained the same size
when swollen for germination.
In the following tables 1 have arranged the species of seeds
on which experiments were made by me, amounting to about
105, into the three groups :
(1) Impermeable group, containing only plants where the
seeds are all normally impermeable.
(2) Variable group, including plants with both permeable
and impermeable seeds.
(3) Permeable group, comprising plants with only per-
meable seeds.
Since the general question of the frequency and distribu-
tion of the quality of impermeability among seeds has been
already dealt with in Chapter III on a far more extended
basis than my own materials would afford, I will merely
confine my remarks on these groups to a few general observa-
92 STUDIES IN SEEDS AND FRUITS
tions before proceeding to describe in detail the results of my
investigation of these seeds from this particular standpoint.
One of the first noticeable things in these groups is the
Thepre- predominance of leguminous seeds in the two groups of
leguminous s P ec i es possessing impermeable seeds exclusively or in part,
plants in the This has already been established by Dr Gola and others, but
groups J J
characterised principally by Professor Ewart from a more extensive experi-
ableeeds. e ence ; and one may be content with showing here how this pre-
dominance is suggestively emphasised in my own less numerous
results. Of the 105 species of seeds named in these groups, 44,
or about two-fifths, are leguminous ; and of these three-fourths
are claimed by the two groups containing plants with impermeable
seeds. If the quality of impermeability was equally distributed
amongst the natural orders, we should expect to find leguminous
plants and plants of other orders about equally represented in
the total of the impermeable and variable groups. As a matter
of fact, however, this is far from being the case, since as many
as 82 per cent, in the groups just named, and as few as 19 per
cent, in the permeable group, are leguminous.
Various points in this classification of seeds will be eluci-
dated as this work proceeds. 1 will, however, notice that the
distinction between the impermeable group, where all the seeds
are impermeable, and the variable group, where both kinds of
seeds are found, is often rather arbitrary. In truth, it would
almost appear from Professor Ewart's tables that very few plants
have seeds that are impermeable without exception. But careful
consideration has convinced me that the real distinction between
the two groups ought to lie not so much in the total absence or
in the presence of permeable seeds, but in the degree of constancy
of the characters within a species. Without some familiarity
with the seeds in question one would be often likely to in-
clude amongst impermeable seeds some that have lost their
imperviousness through a slight defect developed during the
shrinkage process. With typical impermeable seeds there always
will be a very high percentage of seeds normal in this respect ;
whilst with typically variable seeds there will be, as a rule, con-
PERMEABILITY AND CLASSIFICATION 93
siderable variation between different samples, one sample having
a low percentage and another a high percentage of permeable
seeds. This was well brought out in Dr Gola's observations,
already dealt with in Chapter III.
One may add with reference to the short list added to my
tables containing seeds also experimented upon by Professor
Ewart that the only discrepancy is concerned with those of
Leuctenag/auca,vfhich,according to my observations, are regarded
as impermeable instead of permeable, as is indicated in the
Australian experiments.
THE GROUPING OF THE SEEDS EMPLOYED IN
THIS INQUIRY ACCORDING TO THEIR PER-
MEABLE OR IMPERMEABLE QUALITIES
I. IMPERMEABLE
Adenanthera pavonina Leguminosae (S)
Colubrina asiatica Rhamneae (F)
Dioclea reflexa Leguminosae (F)
Entada scandens (F)
Guilandina bonduc (S)
bonducella (F)
(near) glabra (F)
melanosperma (S)
Ipomoea dissecta Convolvulaceae (S)
pes-caprae (F)
tuba (F)
Leucaena glauca Leguminosae (S)
Mucuna urens (F)
Sophora tomentosa (F)
Strongylodon lucidum (F)
Ulex europaeus (S)
Vigna luteola (F)
Note. The capital letters in brackets have the following significations relating to
buoyancy in sea-water :
F = Known to be dispersed by sea- currents, the proportion of buoyant seeds varying
from as much as 80 or 90 per cent, in Guilandina bonducella to as little
as to per cent, in Dioclea reflexa. However, seeds vary much in this
respect in different localities. From my observation of the living plant
in Fiji and Ecuador I formed the conclusion that quite half of the seeds
of Entada scandens have no initial buoyancy ; whereas of fresh seeds
obtained from the plants growing in the Jamaica woods I found that quite
90 per cent, floated (vide the author's Plant Dispersal, p. 181).
S = All sink.
94
STUDIES IN SEEDS AND FRUITS
II. VARIABLE
(Possessing both permeable and impermeable seeds)
Abrus precatorius Leguminosae
95
per cent, impermi
Acacia Farnesiana
70
55 55
Albizzia Lebbek
50
55 55
Aquilegia (species) Ranunculaceae
80
5? 55
Arenaria peploides Caryophyllaceae
80
55 55
Bauhinia (species) Leguminosae
3
55 55
Caesalpinia Sappan
So
55 55
sepiaria
40
55 55
Calliandra Saman
3
55 55
Canavalia gladiata (red
35
55 55
seeds)
obtusifolia
70
55 55
(species)
50
55 55
Canna indica Cannaceae
90
55 55
Cassia fistula Leguminosae
90
55 55
grandis
90
55 55
marginata
9
55 55
Entada polystachya
50
55 55
Enterolobium cyclocarpum
90
55 55
Erythrina corallodendron
60
55 55
indica
50
55 55
velutina
65
55 55
Ipomoea tuberosa Convolvulaceae
35
55 55
Poinciana regia Leguminosae
65
55 55
Thespesia populnea Malvaceae
80
55 55
Vicia sepium Leguminosas
65
55 55
III. PERMEABLE
Achras Sapota (Sapodilla)
Sapotaceae
./Esculus Hippocastanum (Horse-chestnut)
Hippocastaneae
Allium ursinum
Liliaceae
Andira inermis
Leguminosae
Anona Cherimolia (Cherimoya)
Anonaceae
muricata (Sour-sop)
55
palustris (Monkey-apple)
55
reticulata (Custard-apple)
55
squamosa (Sweet-sop)
55
Artocarpus incisa (Bread-fruit)
Artocarpeae
Arum maculatum
Aroideae
Barringtonia speciosa
Myrtaceae
PERMEABILITY AND CLASSIFICATION 95
Berberis (species) Berberideae
Bignonia (2 species) Bignoniaceae
Blighia sapida Sapindaceae
Cajanus indicus Leguminosa
Canavalia ensiformis
Cardiospermum grandiflorum Sapindaceae
Halicacabum
Carica Papaya (Papaw) Papayaceae
Chrysophyllum Cainito (Star-apple) Sapotaceae
Citrus decumana (Shaddock) Aurantiaceae
Crinum (species) Amaryllideae
Datura Stramonium Solanaceae
Dolichos Lablab Leguminosae
Faba vulgaris (Broad Bean)
Fevillea cordifolia Cucurbitaceae
Gossypium hirsutum Malvaceae
Grias cauli flora Myrtaceae
Hedera Helix (Ivy) Araliaceae
Hibiscus elatus Malvaceae
esculentus
Sabdarifa
Hura crepitans Euphorbiaceae
Iris foetidissima Irideae
Pseudacorus
Lonicera Periclymenum (Honeysuckle) Caprifoliaceae
Luffa acutangula Cucurbitaceae
Mammea americana Guttiferae
Momordica Charantia Cucurbitaceae
Monstera pertusa Aroideae
Montrichardia arborescens
Moringa pterygosperma Capparideae
Moronobea coccinea Guttiferae
Opuntia Tuna Cactaceae
Phaseolus multiflorus (Scarlet-runner) Leguminosae
vulgaris (French Bean)
Pisum sativum (Pea)
Pithecolobium filicifolium
Primula veris (Primrose) Primulaceae
Pyrus Malus (Apple) Rosaceae
Quercus Robur (Oak) Cupuliferae
Ravenala madagascariensis Musaceae
Ribes grossularia (Gooseberry) Ribesiaceae
Ricinus communis (Castor-oil) Euphorbiaceae
Scilla nutans Liliaceae
96 STUDIES IN SEEDS AND FRUITS
Stellaria Holostea Caryophyllaceae
Swietenia Mahogani (Mahogany) Meliaceae
* Tamarindus indica (Tamarind) Leguminosae
Tamus communis Dioscoreae
Theobroma Cacao (Cocoa) Buttneriae
Vicia sativa Leguminosae
RESULTS CONCERNING SOME OF THE ABOVE IMPERMEABLE AND
VARIABLE SEEDS FROM PROFESSOR EWART'S TABLES (Prise.
Roy. Soc. Viet. 1908). His results for seeds more than 1 5 or
1 6 years old are not given.
Adenanthera pavonina, seeds 8 years old, swelled after riling.
Albizzia Lebbek, seeds 1 1 years old, scratching needed for
germination.
Canavalia gladiata, 10 years old, I out of 6 seeds required filing
for germination.
Canavalia obtusifolia, 1 6 years old, required sulphuric acid for
germination.
Erythrina indica, of 50 seeds, 8 years old, 6 swelled in water.
Guilandina bonducella, seeds 15 years old, required the acid for
swelling.
Leuctena glauca, seeds 1 5 years old, all swelled in water.
Mucuna urens, 10 years old, required filing for swelling.
Poinciana regia, 9 years old, outer skin impermeable until filed.
imperme- Those who have studied the dispersal of seeds by the
dispersal* by ocean-currents have laid stress on the circumstance that many
water. o f t h e seec } s capable of transportal over wide tracts of sea
belong to leguminous plants ; and I need here only allude
to the circumstance that the four West Indian and Central
American seeds (Dioclea reflexa, Mucuna urens, Guilandina
bonducella, Entada scandens] that are most frequently stranded
intact on the western shores of Europe belong to this order.
When Professor Ewart remarked (p. 1 84) that " macro-
biotic " seeds show no special adaptation for dispersal and
that " none are wind or water-borne," he apparently had
forgotten that there are included in his list the seeds of plants
like Canavalia obtusifolia, Erythrina indica, and Guilandina
* Tamarind seeds absorb water very slowly at first, requiring often an immersion of
a week or more before there is any marked increase in the weight.
PERMEABILITY AND CLASSIFICATION 97
bonducella, that have long been known to be dispersed by
ocean-currents. Putting aside the question of adaptation to
modes of distribution, a view which I hold ought either to be
universally applied or to be discarded altogether, the strand
of a coral island would be deprived of several of its most
conspicuous and typical plants, such as Canavalia obtusifolia,
Colubrina asiatica, Erythrina indica, Guilandina bonducella,
Ipomasa pes-capr<e, Morinda citrifolia t Mucuna (species), Sophora
tomentosa, etc., if their seeds did not possess impermeable coats,
in most if not in all cases associated with the capacity of
prolonged vitality.
Our views of the adaptive relations of impermeability, Imperme-
if it is valid to select cases in a world that is one mass of adaptation,
adaptation, might be a good deal coloured by the station
of the plants investigated. Thus, it might be considered
from a study of the plants of tropical coasts that imper-
meability was most characteristic of the seeds of beach and
estuarine plants dispersed by currents. But it proves to have
no exclusive association either with buoyancy or with a littoral
station. Thus quite a third of the seeds named in my
impermeable group (Adenanthera pavonina, Guilandina bonduc,
G. melanosperma, Ipomxa dissecta, Leucxna gtauca, and Ulex
europ<eui) have no floating powers ; and it may be safely said
that the great majority of the 180 "macrobiotic " impermeable
species of seeds named in Professor Ewart's list have no
buoyancy and no littoral station. In framing any views in
support of the adaptive relations of impermeability in seeds,
it would be wise to cast one's net widely and to adopt the
standpoint taken by Professor Ewart, that there is here a
general adaptation to soil-conditions, without committing
oneself to any mode of genesis of this quality.
I will now deal with some plants of the variable group The lesson
possessing the two kinds of seeds, sometimes differing from possessing 8
each other in external characters as well as in the degree abieandTm"
of impermeability. They will serve to throw some light permeable
on the nature and relations of this quality. Reference has
7
9 8
STUDIES IN SEEDS AND FRUITS
already been made in this chapter to Mr Crocker's description
of the " dimorphic " seeds of Axyris amaranthoides ; and 1 will
now contrast the two types of seeds developed by Entada
polystachya^ not only as regards their external characters, but
also in other associated qualities.
COMPARISON OF THE TWO TYPES OF SEEDS PRODUCED BY
ENTADA POLYSTACHYA.
GENERAL CHARACTERS.
A.
B.
Size in
millimetres.
Permeability
to water.
Colour.
Weight
in
grains.
Hygroscopic
range stated
as a
percentage.
Water-
percentage.
Large,
15x12 mm.
Small,
13x11 mm.
Permeable
Impermeable
Yellowish
brown
Dark
brown
6-6
5'
z'o per cent.
'i >,
lo'opercent.
6'3
Absorption of moisture from the air in the broken condition,
in percentages. )
(Results stated
Not heated.
After exposure for i| hours to a temperature
of 100 to 105 C.
Original
weight.
After Absorbing
4 days. capacity.
Original
weight.
After
heating.
4 days
later.
Absorbing
capacity.
A.
B.
IOO
IOO
101 "6 Hygroscopic
only
109*4 9 '4 per cent.
IOO
IOO
90
937
95
101
less 5*0 per cent,
plus i 'o ,,
Note. The full display of the absorptive quality after heating was not elicited in the
oven-experiments, since the seeds were merely cut in halves in their coats. A period
of at least a week would have been needed for a proper comparison with the absorptive
capacity of the unheated seeds, where the coats and kernels, being treated separately,
were better able to take up moisture from the air.
We see in the above tabulated results that the two types
of seeds exhibited by Entada polystachya differ in all the
critical points that distinguish permeable and impermeable
polystachya. seeds, viz., in water-contents, hygroscopic behaviour, and
absorptive capacity in air ; and we see also that they differ
PERMEABILITY AND CLASSIFICATION 99
equally in colour, size, and weight. The contrast, though
marked, is not quite so great as between typical seeds of the
impermeable and permeable groups, because it is not possible
to use a test that would completely exclude the other type
from a sample without invalidating the experiment, and one
has to select merely by the external characters.
The essential characters of the A type as a permeable
seed are its hygroscopicity, its relatively large water-contents,
and the inability to increase its weight when exposed in a
broken condition to the air, ordinary hygroscopic variation
being sufficient to explain most of the small increase in weight
(1*6 per cent.) noted in the table. On the other hand, B as
an impermeable seed is practically non-hygroscopic, has a
relatively small water-percentage and a counterbalancing large
capacity of absorbing moisture when exposed in the broken
condition to the air. The behaviour after being subjected
to a temperature of 100 C. is also distinctive, the permeable
seeds failing by 5 per cent, to regain their original weight
after an exposure of some days to the air ; whilst the
impermeable seeds ultimately exceed their original weight by
about i per cent. But, as observed in the note to the table,
the full extent of the absorptive capacity after heating was
not determined. These results, however, bring the two
types of seeds into contrast sufficiently well, when we reflect
that each sample of seeds probably contained a small percentage
of the other kind, less easily distinguished than usual by their
external characters.
When seeking for an explanation of these two sets The clue to
of seeds in the same plant, one has not far to look, the the two?" f
uncompleted process supplying the clue. This we recognise ^s^the
in a check to the shrinking and drying process that ushers same plant
i _ r r> A / \ es m a
in the rest-period; and Professor iLwart s surmise (p. 197) check to the
respecting the differences between Acacia seeds of the same
species, that the impermeable seeds are smaller " because they
are drier," goes towards the root of the matter. With the
larger, pale-coloured seeds the shrinking process has been
The cause of
determined*
by variations
in the be-
haviourof
pod. Iymfir
Association
without
acters har "
ioo STUDIES IN SEEDS AND FRUITS
arrested at an earlier stage than in the case of the smaller,
dark-coloured seeds, as is indicated by their size and by their
higher percentage of water. But the behaviour of the smaller
impermeable seeds themselves when they begin to swell for
germination is equally suggestive, since, as soon as they begin
to absorb water, they assume the hue, size, and general
appearance of the larger impermeable seeds.
The whole question is bound up with the history of the
shrinking process of seeds which is discussed in Chapter II,
and behind that lies the story of the maturation and drying
of the fruit. The immediate cause of this check to the
shrinking process of seeds resulting in the production of two
types of normal resting seeds must therefore be looked for
/*~
m the conditions surrounding the final stage or the shrinking
process within the drying legume. In the case of Entada
polystachya the large pods, which are usually 15 or 16 inches
long and 3 inches wide, generally dry on the plant, and as
the outer skin scales off during this process they begin to
break up transversely into separate narrow joints, each con-
taining a seed. It is probable that the check to the shrinking
process of the seeds is determined by variations in the
behaviour of the drying pod with respect to the shedding
of its epidermis and the breaking up into joints. Un-
fortunately, this explanation of the matter only presented
itself to me after the opportunity of further investigation
had passed away.
It is generally necessary, in the case of impermeable
leguminous seeds, that the last stage of the shrinking process
snou ^ ^ e completed in the pod. If one gathers a number
of full-sized so-called unripe seeds in the swollen, soft condi-
tion and allows them to go through the drying and shrinking
P rocess detached from the pod, they will usually fail to become
impermeable seeds. It is also generally necessary that the
seed should remain in the pod whilst it is dehiscing on the
plant, since, if we remove the seeds from the unopened
fruit, even though it is dry and the seeds are in appearance
PERMEABILITY AND CLASSIFICATION 101
normally contracted, they will often prove to have lost their
impermeability.
I will take the case of the seeds of Ctesalpinia Sappan, Caesalpinia
gathered in the Botanic Gardens of Grenada. The seeds on a P pan -
the ground that had fallen naturally from the tree were rather
darker in colour and drier on section than those obtained
from the dry but still closed pods on the tree, though the
last might have been taken for normal seeds, and indeed were
just as capable of reproducing the plant. However, on
keeping a number of the seeds of both kinds under observa-
tion for ten days, I found that those from the closed pods
were slowly losing weight. This led to a detailed comparison
of them with the seeds from the ground, the results of which
are tabulated below and stated in percentages.
COMPARISON OF THE SEEDS OF CAESALPINIA SAPPAN ON THE
GROUND AND ON THE PLANT.
Absorption of moisture from the air in the
broken condition.
Water-
After exposure for i\ hours
Conditions.
Character.
per-
cent-
Not heated.
to a temperature of
100-105 C.
age.
tuo .
bfl
Ija
|H r/i
>
.l-a
S
Ifl
>> u
J-^"
'&.S
*-* rf
O rt
ii '
o
"C v
<ri ^^
'C '5
<J S
rt
in O,
o *
*
^ s
*
Ja
,Q 0!
Seeds lying
Most of
9 '7
IOO
108*9
8 '9 per
IOO
90-3
1047
47 per
loose on
them im-
cent.
cent.
the ground
perme-
able
Seeds from
All per-
13-9
IOO
ioo'5
0-5 per
IOO
86-1
99 '9
Less, o 'i
the closed
meable
cent.
per
dry pod on
hygro-
cent.
the tree
scopic
only
Note. The whole seed (coats and kernel) is used in the absorption experiments.
Thus we get here the same indications as we obtained
in the instance of Entada polystachya, there being from the
gardener's standpoint two sets of seeds, though in nature
IO2
STUDIES IN SEEDS AND FRUITS
probably only one. Those of the closed pod on the tree are
characterised by permeability, by a large amount of water, and
by their inability to increase their weight when exposed in a
broken condition to the air. Those picked up from the
ground are mostly impermeable, and have a low percentage
of water, a deficiency associated with the capacity of consider-
ably adding to their weight by absorbing moisture when ex-
posed as broken seeds to the air. The behaviour of the seeds
of C<esalpinia Sappan is probably typical of many leguminous
seeds with impermeable coats, especially in those cases where
the difference between the seeds would not be readily detected
by the eye. Strong winds and torrential rains would not
infrequently affect the somewhat premature detachment of
the seed from the parent.
The seeds of Ipomoea tuberosa, a convolvulaceous plant, offer
another good instance where divergent behaviour as regards
impermeability is not always associated with conspicuous differ-
ences in the aspect of the seeds. Whilst some of the seeds
swell in water, others have to be filed to induce absorption.
As shown in the results given below for the kernels, imperme-
ability is associated with a relatively small water-percentage and
a considerable absorptive capacity in air after being heated in
the oven. The permeable seeds, on the contrary, contain a large
amount of water and fall far short of their original weight when
absorbing moisture from the air after the heating process.
COMPARISON OF THE BEHAVIOUR OF KERNELS OF IPOMGEA TUBEROSA
AFTER EXPOSURE FOR TWO HOURS TO A TEMPERATURE OF IOO
TO 105 C. (The materials in each case were rather over 100 grains ;
the results are given in percentages.)
Original
weight.
After
heating.
Water-
percentage.
Weight
6 days
later.
Absorptive
capacity
in air.
A. Permeable
IOO
83
i?
93
Minus 7 'o
B. Impermeable .
IOO
9 1
9
103
Plus 3 'o
PERMEABILITY AND CLASSIFICATION 103
The difficulties a seed may have to contend with before
it enters its prolonged rest-period under the protection of
its impermeable skin were brought under my notice in the
case of Diodea reflexa whilst specially studying the habits of Dioclea
this leguminous climber in its home in the mountain forests
of the Grand Etang in the island of Grenada. The rainfall
here is heavy even for the tropics, averaging: 14.0 or i CO ofimperme-
. , , : .. . 5 5 ... . ? ability in its
inches in the year, and very moist conditions prevail in the seeds.
densely shaded woods. The seeds are freed by the decay
of the pod ; and if the detachment of the pod from the
parent takes place under normal conditions, the typical
impermeable seed is produced, such as is at times stranded
by the Gulf Stream with coats intact on the shores and islands
of Western Europe. This tree -climber often favours a
station on the banks of streams and lakes, so that the seed's
opportunities of reaching the open sea are numerous.
But if, as frequently happens, the pods are prematurely
detached during the prevalence of heavy rains and strong
winds, that is to say, before the drying and shrinking stage
of the pod and the enclosed seeds is complete, then the seeds
usually fail to finish the process, and, being moist and permeable,
they either pass on into the germinating condition, a result
favoured by the prevailing humidity of the forests, or decay
and die. These fallen pods lying on the wet, sloppy ground
in the deep shade of the forests readily take up water, and
the seeds, as just remarked, soon swell up and either die or
germinate. On one occasion I noted that out of 30 seeds
obtained from 10 fallen pods lying sodden on the ground in
the depths of the forest, 10 were rotting, 10 were germinating,
and 10 were in a resting condition ; but of these last, 7 or 8
were permeable, with the shrinking process markedly incom-
plete. Even the two or three impermeable seeds were far
from typical in their appearance. It was only occasionally
that a typical impermeable seed was found that seemed fit
for the Transatlantic passage in the Gulf Stream. Such,
then, are some of the difficulties with which a seed may have
104
STUDIES IN SEEDS AND FRUITS
Contrast be-
tween the
permeable
and imper-
to contend in acquiring impermeability. Though no doubt
exceptional in this particular case, they indicate the character
of the obstacles under certain climatic conditions.
The contrast in appearance and in behaviour under different
tests between the permeable seed of Dioclea reflexa where the
shrinking process has been prematurely arrested, and the im-
permeable seed of the same plant where it has been normally
completed, is very striking. The first is brownish black, and
its coats bend, but do not Crack, in the hand-vice. The second
is much lighter in colour, often mottled, and its coats are
relatively brittle. The kernel of the impermeable seed is dry
and almost friable, whilst that of the permeable seed is moist in
appearance and compact in texture. As shown in the tabulated
comparison subjoined, the greatest contrast is presented in the
water-contents and in the capacity of absorbing moisture from
the air after being heated. I may remark here that the behaviour
of the bared kernels during the four hours that passed before
they were placed in the oven was very significant, that of the
impermeable seed gaining nearly 3 per cent, in weight, and that
of the permeable seed losing rather over 3 per cent.
COMPARISON OF AN IMPERMEABLE AND A PERMEABLE SEED OF DIOCLEA
REFLEXA FRESH FROM THE FORESTS OF THE GRAND ETANG IN
GRENADA, AND WEIGHING RESPECTIVELY 83*5 AND 83*1 GRAINS.
BOTH THE COATS AND THE KERNEL WERE EXPOSED TO A TEM-
PERATURE OF 100-105 C. FOR i HOURS. (Results are stated as
percentages.)
-
Original
weight.
Weight
after
heating.
Water-
percentage.
Subsequent increase in
weight by absorbing
moisture during 4 days'
exposure to the air.
A. Impermeable .
IOO
91-4
8'6
108*8, or a gain of 8 -8
per cent, over the
original weight.
B. Permeable
IOO
80-0
zo'o
94'8, that is to say,
failed by 5*2 per cent.
to regain the original
weight.
Note, The behaviour of the separate coats and kernel is essentially the same, and
differs only in degree.
PERMEABILITY AND CLASSIFICATION 105
Whilst showing in the preceding pages that to deficient
shrinkage must be attributed the origin of permeable seeds in
those plants where impermeability is more or less the rule, but
little allusion was made to the changes in the appearance and Changes in
i . . r i T i the condition
condition or the outer seed-coverings in this connection. O f the seed-
Thus, in the case of deficiently shrunken seeds of Entada
scandens, the cuticle is traversed by a network of fine cracks ; lossofi " 1 -
and one of the earliest signs of a normal impermeable seed illustrated by
losing its impermeability is displayed in the development of
these fine cracks. But it is in the seeds of Guilandina bonducella
that we have the best opportunity, though under rather
peculiar conditions, of investigating this subject, and of
observing how deficient shrinkage deprives the seed-coats of
their impervious character.
Whilst describing the stages in the shrinking process of
this seed in a previous chapter (Chapter II), when the con-
nection between deficient shrinkage and loss of impermeability
was first pointed out, no reference was made to the singular
changes in the condition of the outer coats then displayed. It
is very remarkable that the moist, swollen pre-resting seed of
the green unopened pod, though destined ultimately to become
impervious to water, develops during the earliest stage of the
shrinking process a number of parallel transverse fissures or
cracks in the outer coat, and that the seed is only impermeable
when these fissures become closed and hermetically sealed in
the contracted resting seed. In the normal resting seed the
cracks formed in the outer coats during the shrinking stage are
indicated by faint striae, now covered by the enamel-like cuticle ;
but in the deficiently shrunken seed the original cracks are
much more evident and are not sealed over by the cuticle, but
are more or less open, so that the seed is permeable both to air
and water.
If we place in the sun one of these large, soft pre-resting
seeds from the green unopened pod, in a few hours its surface
will be traversed by regular and widely gaping transverse cracks,
and will present the grooved appearance of a boy's top. It is
io6 STUDIES IN SEEDS AND FRUITS
not uncommon to find seeds in this condition on the plant,
when from some cause the pod has opened prematurely or
has been injured in the green closed state. It would seem
from my experiments that, excepting complete submergence in
water, there are no conditions so moist as to prevent the initial
shrinking of the soft, full-sized so-called unripe seeds found
in the green pods of Guilandina bonducella. Two of these
seeds placed in water under cover in Jamaica floated heavily,
showing only a small portion protruding slightly above the
water. Although during three days' immersion they increased
their combined weight from 244 to 253 grains, they both
developed fine concentric fissures in the small portions of their
surfaces that were exposed to the air. On the following day,
having reached a weight of 262 grains, they sank. Here
immersion in water had completely checked the shrinking
process, except in the unsubmerged surfaces exposed to
the air.
One could scarcely imagine a method less likely to produce
impermeability than that followed by the pre-resting or unripe
seeds of Guilandina bonducella. As shown by Miss White in
the appendix to Professor Ewart's paper, and as also brought
out in my own experiments, the seat of impermeability lies
principally in the hard prismatic layer of palisade cells beneath
the structureless cuticle. Yet the cracks formed normally in
the shrinking process are subcuticular, and as the seed contracts
their sides become tightly pressed together, and a layer of
cuticular enamel ultimately covers all.
It may be here remarked that, as in many leguminous
plants, the shrinking of the seed is carried out in its entirety
before the dehiscence of the pod. After the pod has opened,
the seeds in it lie fully exposed to the sun's rays and become
very warm, since the parent plant thrives best on beaches
removed from the shade of trees. On one occasion in Jamaica
I roughly estimated the temperature of the seeds as they lay
in the gaping pod at 150 F. Although this exposure may
add somewhat to the seed's durability by hardening the cover-
PERMEABILITY AND CLASSIFICATION 107
ings, my observations clearly indicated that the seeds acquire
their impervious character in the closed pod.
Any injury of the green pod of Guilandina bonducella is
likely to produce a defect in the impermeability of the resting
seed by interrupting its shrinking process in the pre-resting
state. Very premature dehiscence results in excessive shrivel-
ling of the seed ; whilst dehiscence at a later stage, but before
the seed has completed its normal shrinking, arrests the process
and prevents the development of impermeability, though not
depriving it of its power of germination.
Mould or mildew, by attacking the soft coats of the unripe Mould and
leguminous seed, spoils its prospect of becoming impermeable ^bmty.
by partially destroying the cuticle. At times it extends into
the kernel, and the result is a rotting embryo ; but at other
times the outcome of its attacks is a permeable resting seed,
speckled in places where the cuticle is lacking ; and unless
conditions favouring germination soon arise, the seed shrinks
more and more and finally loses its vitality. These minute
fungi take their place amongst the greatest foes of a seed's
impermeability in the tropics. As illustrated by Entada scandens,
this subject is discussed at length in Note 7 of the Appendix,
and it has been already referred to at the close of Chapter IV.
I may here remark that Dr Gola in Italy made a pro- Dr Cola's
longed experiment on the action of these small fungi on the
impermeability of the seeds of four plants, of which one was
Acacia Farnesiana. After exposing them to moist conditions
for four months, after which they were found to be covered
with mould, he ascertained that the percentage of permeable
seeds was not much increased. Thus, in the case of Acacia
Farnesiana the percentage of permeable seeds was only increased
from 3 to 5 per cent. These indications are not opposed to
my remarks in the preceding paragraph, since Dr Gola ex-
perimented on the hard matured resting seed, which would
be very likely to resist the attacks of minute fungi. It is in
the soft coats of the pre-resting or unripe seed that they find
their opportunity.
io8 STUDIES IN SEEDS AND FRUITS
With regard to the effect of these fungi on the germinative
Mould and capacity of resting seeds in general, all depends on the pro-
tiTO?apatity. tection the seed owes to its coats. With both permeable and
impermeable seeds it would seem that the coverings would
usually offer sufficient protection until the next germinating
season commenced ; but whilst the impervious seeds would be
able to withstand the attack for a long period, it is likely that
the permeable seeds would succumb before a second oppor-
tunity of germinating presented itself. We have just seen
that, as ascertained by Gola, mould affects but little the im-
permeability of resting seeds, an inference that may be extended
to their germinative capacity. With Rape-seed (Saatraps),
which had become covered with these growths after being
exposed for forty-three days in moist conditions, Nobbe
(p. 107) found that 85 per cent, germinated, the germinative
capacity of the sample being 99 per cent. Since these seeds
swelled in water, they would illustrate the behaviour of perme-
able seeds in this respect.
It would seem, therefore, that the resting seed in its
Mould is the hardened coats is fairly proof against the attacks of mould,
soft^unripe and that speculations as to the direct influence of these small
fungi on seeds must be restricted to the seed in its unprotected
state, as when it is prematurely exposed in the soft condition
through the untimely opening of the fruit. Nature usually
ensures the safety of the seed by securing that its coverings
harden before the exposure to the outer world takes place.
As shown in a subsequent chapter, the hardening of the seed-
coverings precedes the opening of the fruit, whether moist
or dry, whether rupturing through decay or dehiscing in a
regular manner. Were it otherwise, propagation by seed
would become impossible except in regions where mould and
mildew are infrequent. There seems at first glance a special
provision here ; but one could read the same into every detail
of a plant's life-history. In a world where all is adaptation it
seems idle to employ the term at all. Yet in the tropics one
would be strongly tempted to use the phrase in this matter of
PERMEABILITY AND CLASSIFICATION 109
fruits, seeds, and minute parasitic fungi. In my experiments
in those regions, I found it very difficult to dry the bared
kernels of seeds, or to dry seeds which had been cut across,
since mould used to form in a few days on the unprotected
or cut surfaces.
But to return to the principal theme of this chapter, I
think enough has been said to connect with deficient shrinkage The connec-
the origin of permeable seeds in plants where impermeability permeability
is more or less the rule. Here, then, permeability is associated complete
with insufficient drying. Various allusions of similar signifi- shrinkage is
. . , J , . . established
cance occur in different parts or this work, and 1 have shown in this
that the trend of Professor Ewart's observations on the seeds cha P ter -
of the Australian Acacias is in the same direction. But clear
as the indications may seem, there has been another view of
the origin of impermeability during the seed's maturation
which has been advanced by Dr Gola. It is requisite to
remember that by an impermeable seed we always imply a
seed impervious to water ; and this will explain why mention
is not made in this connection of the recent researches of
Becquerel, which refer principally to imperviousness to air
produced by the desiccation of certain normally permeable
seeds, such as Peas, Beans, and Lupines (Annales des Sciences
Naturelles Botanique y 1907).
Dr Gola's view, as stated not only in his original memoir, Dr Cola's
published in 1905 by the Royal Academy of Science of Turin, ne'ctinghn-
but also in the summary he himself contributed to the ^^^ llty
Botanisches Centralblatt in 1906, is that the impermeability maturity,
of its coats is due to the seed's insufficient maturation under
the influence of such climatic and local factors as cold, drought,
great humidity, excessive shade, etc. In order to show that
impermeability goes with immaturity, he gives in a table the
results of experiments on the seeds of seven species of
leguminous plants of the genera Acacia^ Cytisus, Genista^
Robinia, and Trifolium, in which he connects the greater
tendency to absorb water with the greater maturity of the
seed. As given in Note 8 of the Appendix, where the table is
no STUDIES IN SEEDS AND FRUITS
reproduced, the results do not appear convincing. With the
exception of two of the species experimented on, there is but
slight contrast in the behaviour of the more mature and less
mature seeds, and even in those two cases the contrast is not
striking. Then, again, in the instance of the seeds of the
species of Acacia (A. Farnesiana\ it would be difficult to draw
any inference from the circumstance that the less matured
seeds contained no permeable seeds and the more matured
8 per cent., when the value given in the general table for the
ordinary mature seeds is 3 per cent. I must be pardoned
for saying that, as presented, the differences are too small to
serve as the basis of a theory, whilst the data are hardly
sufficient in quantity. Then, again, the expressions " more
mature " and " less mature " can only apply to the condition
of the coats, since the embryo is as fully mature in the soft
full-grown seed of the green pod as it is in the normal resting
seed.
Still, the trend of the indications would be in favour of
Dr Gola's interpretation in default of a more probable ex-
planation. I made a long study of the shrinking process in
seeds, and all my results point to the opposite conclusion,
namely, that the occurrence of permeable seeds amongst
typically impermeable seeds is due to deficient shrinkage, or,
in other words, that immaturity is associated not with imper-
meability but with permeability. Professor Ewart's extensive
researches yielded results supporting the same conclusion ;
and one may recall his remark (p. 197) concerning leguminous
seeds (the same order tested by Dr Gola in this connection),
that the seeds which take up water with difficulty are smaller,
drier, and in appearance harder than the readily swelling ones
of the same species.
It often occurred in my own investigations that shrivelled
very immature seeds absorbed water less readily than seeds
still immature, though less shrunken. But this was not the
test of maturity employed by Dr Gola. Adopting the con-
clusion that the complete absence of chlorophyll in the integu-
PERMEABILITY AND CLASSIFICATION in
ments is the index of perfect maturation, he proceeded to study
the question of permeability from that standpoint. Taking
only " germinable " seeds, he finally inferred that the greener
seeds are the less mature and the more impermeable. The
general trend of my observations is all against such a view,
deficient shrinkage and loss of impermeability being uniformly
associated. The green colour of imperfectly shrunken seeds,
where the normal resting seed was impermeable, often came
under my notice ; but always connected with loss of im-
permeability more or less complete.
Taking the seeds of Acacia Farnesiana, the shrinking process
of which I observed in Grenada and Jamaica, I found that
full-sized so-called unripe seeds, when allowed to go through
the shrinking stage detached from the pod, remained green,
though in other respects resembling the normal brown resting
seed. I did not test their permeability, but since 85 per cent,
of the brown seeds from the same plants proved to be im-
permeable, the margin of possible advantage left for the green
seeds was small. Dr Gola's results have proved of so much
service to me that one feels loth to dissent from him when he
associates impermeability with immaturity ; but I feel confident
that should he ever extend his researches to the shrinking
process of seeds, he will arrive at a different conclusion.
This chapter may be concluded with the remark that there
are several points in the behaviour of seeds, notably those
concerned with the differences in the water-contents of perme-
able and impermeable seeds, and with their absorptive capacities
after the oven test, which will be further elucidated in the
succeeding chapters, especially in that dealing with Hygro-
scopicity.
SUMMARY
(i) According to the existence or absence of impermeable cover-
ings, seeds are here divided into three groups : (a) impermeable, where
all the normal seeds are impermeable to water ; (b] permeable, where
all the seeds are permeable ; and (c) variable, an extensive group
ii2 STUDIES IN SEEDS AND FRUITS
where both kinds of seeds occur in the same plant, sometimes, but not
usually, distinguished also by external characters. It is the variable
group that ofFers the best materials for study (p. 91).
(2) The author then gives the list of about 105 species of seeds
on which he experimented, arranged in these three groups. Two-
fifths of them are leguminous, and of these three-fourths are claimed
by the two groups with impermeable seeds, a fact indicating the pre-
dominance of impermeable seeds amongst the Legummosae as compared
with other orders, and previously established by the researches of
Nobbe, Gola, Ewart, and others (p. 93).
(3) It is shown that impermeable seed-coats, whilst characterising
both buoyant and non-buoyant seeds, are indispensable for seeds that
are transported by currents, and that the coral island in mid-ocean
would be deprived of many of its most conspicuous plants if their
seeds were pervious to water. The author proceeds to point out that
as regards the adaptive relations of impermeability it would be wise to
cast one's net widely and adopt the standpoint of Professor Ewart that
in seed-impermeability we have a general adaptation to soil-conditions
(P- 97)-
(4) The lesson of the plants possessing both permeable and im-
permeable seeds distinguished by external characters is supplied by
Entada polystachya. In this connection it is remarked that the clue
to the origin of these two kinds of seeds in the same plants lies in the
shrinking and drying of the soft pre-resting seed, a process which is
completed in the impermeable seed, but arrested at an earlier stage in
the permeable seed. The cause of the check in the shrinking and
drying of the seed is determined by variation in the behaviour of the
drying pod (p. 98).
(5) The same indications are supplied by those numerous plants where
permeable and impermeable seeds are associated without differing much
in their external characters, as illustrated by Ctesalpinia Sappan and
Ipomcea tuberosa (p. lOl).
(6) The difficulties that may attend the development of imperme-
ability in seeds are then illustrated in detail from a study of Dioclea
reflexa in the forests of Grenada (p. 103).
(7) The changes in the condition of the seed-coats associated with
loss of impermeability are exemplified by Guilandma bonducella (p. 105).
(8) Mould or mildew, by attacking the soft coats of the seed in
the moist green pod and destroying the cuticle, is regarded as one of
the greatest foes to the development of impermeability. That typical
hard resting seeds may be largely proof against the attacks of these
minute fungi has been shown by the experiments of Nobbe and Gola.
But the author observes that it is not there we should look for risks to
the seed from this cause, since it is the so-called unripe soft-coated seed
PERMEABILITY AND CLASSIFICATION 113
before shrinkage and hardening have begun that offers to these fungi
their opportunity (p. 107).
(9) After remarking that the connection between permeability
and insufficient shrinkage has been established in this chapter, the
author proceeds to discuss Dr Gola's view connecting impermeability
with immaturity and shows that his theory cannot be sustained
(P- 109).
(10) The reader is reminded that many features in the behaviour
of permeable and impermeable seeds, especially those concerned with
their capacity of absorbing water from the air after being exposed to a
temperature of 100 C., will be elucidated in subsequent chapters,
particularly in that on Hygroscopicity (p. in).
CHAPTER VI
Additional
experiments
by punctur-
ing or filing
impermeable
seeds.
ADDITIONAL EVIDENCE ON THE CONTRAST IN BEHAVIOUR
BETWEEN PERMEABLE AND IMPERMEABLE SEEDS
THIS chapter contains the bulk of the data on which are based
the distinctions in behaviour between impermeable and
permeable seeds as typified by those of Guilanaina bonducella
and Canavalia ensiformis in Chapter IV. Some of their
differences, such as those concerned with hygroscopicity and
permeability, will be found generally treated in the preced-
ing and in following chapters. Here we are at first more
especially concerned with the distinctions in their behaviour
when bared or punctured or broken up and exposed to the air.
We will take first the additional evidence concerning the
effects of puncturing or baring the three types of seeds
described in the preceding chapter the impermeable, the
variable, and the permeable and will commence with some
additional results of experiments on punctured impermeable
seeds. The effect of increasing the weight through the
absorption of water from the air has already been discussed in
the case of Guilandina bonducella in Chapter IV. The results
for the seeds of Entada scandens in an experiment covering two
years are tabulated below.
[TABLE
114
ADDITIONAL EVIDENCE
RESULTS OF EXPERIMENTS ON SEEDS OF ENTADA SCANDENS BY FILING
INTO THE SEED-COATS. (The five seeds employed varied from 323
to 430 grains, but the results are stated in percentages.)
|
M
U)
u*
u>
U)
*5
I)
43
j*
3
J3
,G
00
1
E
li
U
V
|
a
o
S
O
H
I
S
O
O
>.
"C
U
G
4-
M
*
j*j
JT
oo
N
"
O
^
A. With coats
IOO
IOO
IOO
IOO
IOO
IOO
100
IOO
IOO
IOO
intact
B. Filed into
IOO
100*2
100*3
ioo '6
lOI'I
101 *6
ioo'9
IOI 'I
101*3
100*7
middle layer
of the coats
C. Do.
IOO
100*3
1 00*4
100*8
101*5
101*4
100*5
D. Filed
IOO
100*5
1 00*7
101*3
102*4
102*8
101-8
through the
coats, ex-
posing the
kernel.
E. Do.
IOO
100*2
100*3
ioo'6
101*3
101 *4
100*4
100*7
lOI'I
lOO'I
Note. The actual variation of A was only 406*5 to 406*6 during the two years.
Seeds C and D failed to germinate when tested ; the others were not tried. Probably
the failure was due to the method employed, since seeds of Guilandina bonducella,
subjected to a similar experiment, germinated healthily, after remaining for two years in
the condition of B and D. (See Chapter IV.)
The indications given in Chapter IV as regards the relative
effects on the subsequent weight of impermeable seeds of
puncturing the coats and of removing them altogether may
here be supplemented. As before remarked, the increase in
weight through the absorption of water from the air is more
rapid when the seed is bared than when it is merely punctured
or filed, the maximum weight being usually attained in a few
days in the one case, whilst the gain in the second case is ex-
tended over several weeks and even months. In Chapter IV
it has been already shown in the case of a typical experiment on
the seeds of Guilandina bonducella that whilst the bared kernels
reached their maximum weight of 14 or 15 per cent, in excess
during five days, the filed seeds occupied four or five months in
increasing their weight 10 or 1 1 per cent. The punctured seeds
of Entada scandens behave in the same tedious way as indicated
in the tabulated results above given, whilst the bared kernels
Impermeable
seeds gain
weight far
more rapidly
when bared
than when
punctured or
filed.
n6
STUDIES IN SEEDS AND FRUITS
attain their maximum weight in a few days. If a number of
seeds are bared together in the same experiment, the increase of
weight might astonish the observer when unprepared for such
a result. A sample of 1000 grains of the seeds of Guilandina
bonducella would in less than a week weigh from noo to
1 1 80 grains; but even the testimony of the bared kernel of
a single seed as given below would be sufficiently striking.
The following data represent the result of an experiment
on a single bared kernel of Guilandina bonducella :
Original weight
After i day .
4 days .
55 7 55
1 5' i grains
16-8
*7'7 55
17-0 55
The range of
the increase
of weight of
the bared
kernels of
Guilandina
bonducella.
Ji -* JJ I ft
Gain in weight . . . 17-2 per cent.
Although five or six days are usually sufficient in the case
of this and other impermeable seeds for the attainment of the
maximum weight, the period may be as short as three or as
long as ten days, the time being extended or shortened by
the relative dryness or humidity of the air. The varying
hygrometric conditions of the air also account for some of the
differences between the results of experiments, but only to the
extent of 2 or 3 per cent., which represents the ordinary range
of hygroscopicity. The results of six experiments on the bared
kernels of Guilandina bonducella^ mostly in the West Indies, the
average weight of a kernel being 1 6 or 17 grains, are given below.
RESULTS OF EXPERIMENTS ON THE BARED KERNELS OF GUILANDINA
BONDUCELLA, SHOWING THE INCREASE IN WEIGHT BY THE ABSORP-
TION OF AQUEOUS VAPOUR AFTER AN EXPOSURE OF A FEW DAYS
TO THE AlR.
Number of
Locality of
Gain of weight
kernels.
experiment.
in air.
i
Jamaica
10*2 per cent.
i
17-6 ,
i
17-2 ,
3
Grenada
15-0
3
England
10-2 ,
3
Grenada
16-2 ,
ADDITIONAL EVIDENCE 117
These results indicate a range of from 10 to 17 per cent,
in the increase of weight which recently collected seeds of
Guilandina bonducella experience on being deprived of their
coverings. If we allow for the usual hygroscopic reaction, this
would probably represent a true range of 12 to 15 per cent.
One other impermeable leguminous seed may here be
specially mentioned in connection with the variations in its
increase of weight on being exposed to the air after being
deprived of its coverings. Four samples of kernels of Entada The range
J*
scandem weighing from 100 to 260 grains increased their scandens*
weight during an exposure to the air of from four to ten days
by 4-2, 5*7, 6-8, and 12*2 per cent. The last result was
obtained during humid weather in Jamaica ; and it is evident
from the progress of the experiment which is shown below that
if allowance is made for the hygroscopic reaction (that is, by
deducting half the variation), the excess weight would not have
been much over 10 per cent.
I here append the particulars of this experiment in Jamaica
on the bared kernel of Entada scandens, which is noteworthy as
illustrating the rate of increase and the effect of the ordinary
hygroscopic reaction on the materials.
Original weight . . . 100 grains
After 7 hours . ., . 102-3
i day .... 106-5
2 days . . . 109-1
3 . . . no-8
4 . . 1 12-2
5 . . . . 112-25
6 . . . no-8
7 IIO '
10 . . . . 1 1 1-5
14 . . . 108-1
16 . . . . ui-i
The average results of my experiments on the bared
kernels of these and other leguminous impermeable seeds are General
tabulated below, together with those for two species of impermeable
Ipomcea ; and it is of importance to note in passing that seeds seeds -
n8
STUDIES IN SEEDS AND FRUITS
of such a different order (Convolvulaceae) display the same
quality when impermeable.
TABLE SHOWING THE USUAL INCREASE OF WEIGHT THROUGH THE
ABSORPTION OF WATER FROM THE AIR DISPLAYED BY IMPERMEABLE
SEEDS, EITHER AFTER BEING BARED OF THEIR COVERINGS OR AFTER
BEING CUT ACROSS IN THEIR COATS. (All are leguminous excepting
the two last.)
Gain in weight after exposure to
Name of species, with average
the air for 5 to 7 days.
Locality
weight of a single seed.
Bared kernels.
Cut in halves in
OI
experiment.
their coats.
Adenanthera pavonina (5 grains)
2 '9 per cent.
England.
Dioclea reflexa (100 grains) . . -{
io'6
6'o
-
Grenada.
England.
Entada scandens (400 grains) . -f
5*5
IO'O
Jamaica.
Guilandina bonduc (50 grains)
8'2
England.
f
15-2
Grenada and
, , bonducella (40 grains) -!
Jamaica.
I
I0'2
England.
,, glabra (65 grains)
6-0
M
Leucsena glauca (o - 8 grains)
5 "o per cent.
Grenada.
Mucuna urens (90 grains)
6 '2 per cent.
England.
Strongylodon lucidum (40 grains]
5 '2 per cent.
ii
Ulex europseus (o'i grain) .
S' ,
Ipomcea dissecta (2*5 grains)
6 'o per cent.
Jamaica.
,, pes-caprse (3 grains)
4 'o per cent.
England.
The seeds in the foregoing list vary greatly in size and
weight, from those of Leucsena g/auca, which average only
0*8 of a grain, to those of Entada scandens, which average
400 grains. The samples of kernels used were generally
50 to 100 grains, but greater in the case of the large seeds.
The hygroscopic reaction is as far as possible excluded. It
will be inferred that it is not possible to strike an average
increase of weight for the bared kernels of impermeable
seeds when exposed to the air. Each kind of seed has its
own regime in this respect, which is influenced not only
by the relative dryness of the kernel, but also by the
amount of oil it contains. This probably explains the
small excess weight of the seeds of Adenanthera pavonina.
ADDITIONAL EVIDENCE 119
Speaking very generally, however, we may infer that legu-
minous impermeable seeds when bared commonly increase
their weight from 5 to 10 per cent, by abstracting moisture
from the air.
A question of interest here presents itself as to the
duration of the ultra-dryness of the kernels of impermeable
seeds. My materials for furnishing an answer, though
insufficient, tend to show that this condition may be main- Duration of
tained for several years. A seed of Mucuna urens, gathered
by me from the plant in Hawaii eleven years before,
increased its weight when bared of its coats in England
6*5 per cent, in ten days. In the same way, the bared
kernels of two seeds of Guilandina bonducella obtained by
me in Fiji ten years before added 7*2 per cent, to their
weight ; and a seed of Strongylodon lucidum, picked up amongst
the drift on a Fijian beach eleven years before, and perhaps
a year or two old then, increased its weight by 6 per cent,
when bared in England of its coats. In the case of the
two last-named species, seeds collected at the same time and
place and tested for germination at the time of the above
experiment germinated healthily and supplied plants for my
greenhouse.
There is but slight indication here of any marked decrease
in the ultra-dryness of impermeable seeds during a period of
ten or eleven years. The increase in weight (6-5 per cent.) of
the seed of Mucuna urens is rather above the average (6-0 per
cent.) for three seeds, six to eighteen months old, which were
also tested in England. On the other hand, the rate of increase
for the Fijian seeds of Guilandina bonducella ten years old
(7-2 per cent.) is considerably under the average for the
tropics (15 per cent.). However, the contrast is not nearly so
great as it appears, as the Fijian seeds were experimented on
in England, and, as shown in the table below, the rate of
increase of the weight of the bared seeds of Guilandina
bonducella in a temperate climate would average only about
10 per cent.
I2O
STUDIES IN SEEDS AND FRUITS
There are two other points to be referred to in connec-
tion with the behaviour of the bared kernels of impermeable
seeds, namely, the respective influences of tropical and
temperate climates on the gain in weight in air, and the
duration of this excess weight. We would expect the bared
kernel of a tropical seed to gain more water from the air
in the more humid climate of the West Indies than in
the drier climate of the south of England. We should
also expect the excess in weight to be permanent yet subject
to the ordinary hygroscopic reaction, as long as the seed
retains its vitality.
RESULTS OF EXPERIMENTS ON THE SEEDS OF THE SAME PLANT IN THE
TROPICS (WEST INDIES), AND IN THE SOUTH OF ENGLAND.
The in-
fluence of a
temperate
climate on
the absorp-
tive capacity
of bared
impermeable
tropical
seeds.
Place of
experiment.
Gain of weight
in air of
bared kernel.
Jamaica
M
io'2 per cent.
17-6
Guikndina bonducella .
Grenada
17-2
15-0
16-2
England
IO'2
Entada scandens .
11
57
6-8
Dioclea reflexa . . . -!
Jamaica
Grenada
England
IO'2
io'6
6'o
The first point is illustrated in the foregoing table. Since
the seeds there referred to, as well as those named below, are
all tropical, the question, as far as this investigation is con-
cerned, relates to the influence of a temperate climate on the
capacity of the bared kernels of impermeable tropical seeds of
increasing their weight by absorbing water from the air. The
data of the table indicate that the absorptive capacity is
diminished in temperate climates.
The next point is concerned with the permanence of
the excess weight acquired by the exposure to air of the
ADDITIONAL EVIDENCE 121
bared kernels of impermeable seeds. This has already
been noticed in the case of the seeds of Guilandina bondu-
cella in Chapter IV, where it is shown that after the first
gain of 13 per cent, the weight began to diminish slowly, The degree
though even after two years there was still an excess of manenceof
3 per cent., allowing for the hygroscopic variation. This the excess
loss of the excess weight in time is not at first sight easily acquired by
explained. However, since the bared seed in absorbing rneable
water from the air assumes the r61e of the kernel of a seeds>
permeable seed, it is likely that light may be thrown on it
when we come to discuss the final fate of permeable seeds
in time.
On the other hand, a different indication is offered where
the seed is punctured or filed, when the gain in weight takes
place very slowly. Thus it is shown in the table of results
given in Chapter IV for punctured seeds of Guilandina bondu-
cella that the punctured seeds occupied some months in reaching
the maximum excess weight of 10 or n per cent., and even
after two years were still 7 or 8 per cent, heavier than before
they were punctured or filed.
However, experiments of this kind being always con-
ducted under dry conditions are by no means imitations
of what occurs in nature, though they indicate latent
properties or potentialities of impermeable seeds. In the
home of the plant, such a seed, if deprived by some defect
or injury of the proper protection of its impervious cover-
ings, would either pass on to the germinating stage or
would become mouldy and decay. But it is only with
those seeds where there is a great increase in weight, such
as occurs with the bared kernels of Guilandina bonducella,
that one can test the duration of the excess weight by
eliminating the ordinary hygroscopic reaction of 2 or 3 per
cent. Impermeable seeds, when deprived of their coats,
gather weight during the first week or two independently to
some degree of the atmospheric conditions. After this they
respond normally to the changes in the hygrometric state of
122 STUDIES IN SEEDS AND FRUITS
the air ; and if the excess weight, due to the absorption of
aqueous vapour by the ultra-dry kernel, is only 3 or 4 per
cent., it is difficult to exclude the disturbing influence of the
hygroscopic reaction. Such experiments in the tropics are
likely to be terminated by attacks of mould, and even in
England it is necessary that they should be carried out in a
dry room. The appearance of mould is usually preceded
by a marked increase in weight. The bared kernels of an
inland Jamaican species of Guilandina gained about 6 per cent,
in weight during the first ten days, and, subject to slight
variation, preserved this excess for about two months, when
very damp weather followed, and the seeds, after having
augmented their weight to 10 per cent., were attacked by
mould.
With regard to the " variable " group of seeds, where
both permeable and impermeable seeds occur in the same
plant, only a few remarks will be needed before giving the
tabulated results of my observations. As concerning the
The capacity bared kernel's capacity for absorbing water from the air,
kernels of 6 these seeds exhibit the extreme behaviour of the perme-
variable a ^l e and impermeable seeds, in the first case merely the
seeds of ..... J
absorbing ordinary hygroscopic variation of I or 1*5 per cent, on
the air. either side of the mean, in the second case a marked and
permanent increase often of 10 per cent, or more. If
we had to handle two samples of seeds from the same
plant which presented this great contrast in behaviour, we
should at once know that one sample consisted only of
permeable seeds and the other sample only of impermeable
seeds. Almost always, however, the sample would be mixed,
and then we should get an intermediate result, for instance,
an average increase of weight, after allowing for the hygro-
scopic reaction, of 4 or 5 per cent. Some seedsman, more
practical than the author, might be able to make a scale of
comparison which could be used for proving his seeds ; but
it would be requisite to have a standard of comparison for
each species.
ADDITIONAL EVIDENCE
123
RESULTS OF OBSERVATIONS ON THE CAPACITY OF VARIABLE SEEDS OF
INCREASING THEIR WEIGHT BY ABSORBING WATER FROM THE AlR,
EITHER AFTER BEING COMPLETELY DEPRIVED OF THEIR COATS, OR
AFTER BEING CUT ACROSS IN THEIR COATS. (The hygroscopic
reaction is excluded.)
Note. The term "variable" is applied when a plant produces both permeable and
impermeable seeds. With small seeds it is often more convenient to expose them to the
air cut in halves than to bare their kernels. The difference in the results of the two
methods is not very great, and will be dealt with in the next chapter. The letters
A, B, C, indicate only approximate estimates.
A. Sample where most seeds are permeable.
B. ,, ,, impermeable.
C. ,, they are equally mixed.
Ot
S
a
en
Gain in weight after exposure to
air for 5 days or more.
Locality
of experi-
ment.
Bared
kernels.
Cut in halves
in their coats.
Abrus precatorius . . -{
A
B
i 'o per cent.
S'
England.
ii
Acacia Farnesiana
C
2 'o per cent.
Grenada.
Albizzia Lebbek .
C
2-2
,,
Bauhinia (species)
A
Hygroscopic only
England.
Caesalpinia Sappan . . \
A
B
i 'o per cent.
9'o
Grenada.
/
A
Hygroscopic only
Jamaica.
, | sepiana . . ~
B
7 "o per cent.
...
it
Canavalia gladiata . . j
A
B
Hygroscopic only
5 'o per cent.
England.
,, obtusifolia .
B
6 *o per cent.
Canna indica
Hygroscopic only
Cassia fistula
B
...
3 'o per cent.
,, marginata
B
I- 9
Entada polystachya . . {
A
B
i '6 per cent.
9'4
Grenada.
r
B
3 '5 per cent.
Enterolobium cyclocarpum . -j
B
{3 '3 percent. 1
(a'S) ,, /
...
England.
Erythrina corallodendron . -{
C
/ 3-o I
1(2-6) ;
...
ii
I
C
2 '4 per cent.
i)
A
'5
Grenada.
A
2'3 it
ii
B
6-2
C
...
4'5
England.
C
/ 5 *o per cent. \
1(4'*) .. /
...
,, velutma
B
xo'o ,,
Jamaica.
Ipomcea tuberosa . . {
A
B
Hygroscopic only
4 '6 per cent.
England,
it
Poinciana regia .
A
Hygroscopic only
11
Note. The figures in parenthesis in the "bared kernels " column indicate the result
when the coats are included, thus enabling a comparison to be made with the data in
the next column.
I2 4
STUDIES IN SEEDS AND FRUITS
The effect of
depriving a
permeable
seed of its
coverings.
The effect of baring a permeable seed has been already
referred to in Chapter IV in the instance of Canava/ia
emiformis. Since the kernel is placed in hygrometric relations
with the atmosphere by its porous coats, one would not look
for any marked result with seeds that have completed the
drying process. Indeed, the immediate effect on a seed that
has reached a stable weight is merely to give a rather freer
play to ks hygroscopicity. There is, as one would expect, no
attempt to permanently increase its weight. The contrary is,
in fact, the case with a seed that has yet water to yield to the
air, since the drying process is accelerated by the removal of
its coverings. The contrast between permeable and imper-
meable seeds in this respect is well exhibited in those plants
producing both types capable of being readily distinguished by
the eye, as shown in the results below tabulated.
Character
of seed.
Effect of exposing the bared kernels
to the air for 4 or 5 days, stated
as a percentage of the original weight.
f
Permeable
Gained i '6 per cent. ; mainly hygro-
Entada polystachya .
A
scopic.
(
Impermeable
Gained 9*4 per cent.
t
Permeable
Varied only 0*7 per cent. ; entirely
Csesalpinia Sappan .
A
hygroscopic.
(
Impermeable
Gained 9 *o per cent.
I made a large number of observations on the effect of
baring the kernels of permeable completely air-dry seeds, on
the results of which are based the above general conclusions.
As examples of permeable seeds which merely continue to
behave hygroscopically on the 'removal of their coverings,
though often in an increased degree, the following may be
cited :
Achras Sapota (Sapodilla)
Anona muricata (Sour-sop)
palustris
reticulata (Custard Apple)
squamosa (Sweet-sop)
Canavalia ensiformis
ADDITIONAL EVIDENCE 125
Cardiospermum grandiflorum
Chrysophyllum Cainito (Star Apple)
Citrus decumana (Shaddock)
Dolichos Lablab
Faba vulgaris (Broad Bean)
Hura crepitans (Sand-box Tree)
Luffa acutangula (Loofah)
Phaseolus multiflorus (Scarlet-runner)
Pisum sativum (Pea)
Ricinus communis (Castor-oil)
Of the thirteen genera here named five are leguminous and
the rest belong to a variety of other families. This list is
simply intended to illustrate the subject. A number of
additional examples might have been given ; whilst others,
like the seeds of the Horse-chestnut (/Esculus Hippocastanum}
and of Acorns (Quercus), will be more fittingly dealt with in
discussing the drying process of permeable seeds. In this
connection it should be observed that this matter has only been
handled here in so far as it brings out the contrast in behaviour
between permeable and impermeable seeds when deprived of
their coverings.
The ultra-dryness of impermeable seeds as compared with Additional
permeable seeds which has been disclosed by the various theassocia-
experiments above discussed is confirmed by the evidence tionofthe
' ultra-dryness
supplied when the seeds of the different types are exposed to of imperme-
a temperature of 100 C. In other words, it is associated with with a low
a low water-percentage. This was established for the seeds of
Guilandina bonducella in Chapter IV. Here 1 will illustrate it
by a number of fresh examples and will discuss the subject,
therefore, from a more general standpoint. For this purpose
all my results for the three types of seeds are given in the
table in a later page of this chapter.
There is but little significance in this feature of impermeable
seeds until it comes to be contrasted with the behaviour of
permeable seeds ; and even then the contrast must be made
with discretion. For instance, if we were to compare imper-
meable leguminous seeds indiscriminately with permeable seeds
126
STUDIES IN SEEDS AND FRUITS
The neces-
sity of con-
fining the
inquiry to
seeds of the
same order.
Leguminous
impermeable
and perme-
able seeds
contrasted.
of other orders, we should find that there is often no sort of
relation between them as regards the capacity of absorbing
water from the air in the broken condition and the actual
water-contents as indicated by the loss of weight in the oven.
For example, an average impermeable seed which contained
9 per cent, of water would be able to increase its weight by
about 7 per cent, when broken up and exposed to the air.
It would be ultra-dry in the entire condition to that extent.
On the other hand, this percentage of water in oily seeds like
those of Ricinus or Hum or El<eis would be no indication of
dryness in the seed, since except for the hygroscopic variation
they would remain unchanged in weight on exposure to the
air in the broken condition. Here matters are on quite
another plane, and for a valid comparison of seeds of different
orders we must not look in this direction. It is therefore
requisite, if we wish to connect the seed's capacity of in-
creasing its weight by abstracting water from the air with its
deficient water-contents, that we should restrict the comparison
to seeds of the same order. In this case we take leguminous
seeds ; but even here disturbing influences may come into
play, though they are more easily avoided.
So, confining ourselves at present to the Leguminosae, we
will at first refer to the indications afforded by impermeable
seeds in the table that a seed's capacity of increasing its weight
when bared of its coats or in the broken condition is determined
by a low water-percentage.
We can see at once in the results for impermeable
leguminous seeds that the seeds which lose least weight when
submitted to a temperature of 100 C. are those which add
most to their weight when exposed unprotected to the air.
Thus, we see that the three kinds of seeds with the lowest
water-percentage, Dioclea reflexa, Guilandina bonducella^ and G.
bonduc^ are those which add most to their weight when exposed
to the air. On the average these seeds with a water-percentage
of 7*5 per cent, add 9-2 per cent, to their weight when exposed
in the broken condition to the air. The other impermeable
ADDITIONAL EVIDENCE 127
leguminous seeds (Adenanthera pavonina, Entada scandens,
Mucuna urens] give an average gain in air of 5-0 per cent.,
with an average water-percentage of Try. These results may
be accepted tentatively as representing the average behaviour of
impermeable seeds when broken up and exposed to the air, viz. :
Seeds holding 11-7 per cent, of water gain 5-0 per cent.
j> 7'5 j> jj 9*2 jj
' At best this is only a rough indication, as each seed has a
regime of its own in this respect. The real significance of
these figures becomes more apparent when we contrast them
generally with those for permeable seeds of the same order,
taking as our examples the seeds of Canavalia ensiformis, Faba
vulgaris (Broad Bean), Phaseolus multiflorus (Scarlet-runner),
and Pisum sativum (Pea), which hold on the average about 1 5
per cent, of water when the drying process is complete, and make
no permanent addition to their weight when broken up or cut
open or laid bare and exposed to the air. Contrasted with
impermeable seeds we get these general results :
Impermeable seeds holding 7-5 per cent, of water add 9-2 per cent.
to their weight.
Impermeable seeds holding 11-7 per cent, of water add 5-0 per cent.
to- their weight.
Permeable seeds holding 15-0 per cent, of water add cro, behaving
hygroscopically.
Numerous disturbing influences come into play in making
a rough estimate, such as that given above ; but its general
indications are confirmed by the results obtained from experi-
ments in which such influences are largely eliminated, namely, The elimina-
by contrasting the seeds of the same plant in those species tutting in-
where both permeable and impermeable seeds are represented, Jj^jjJjJm 7
namely, in the variable group. But even here, as indicated seeds of the
in the table, we must be able to distinguish between samples where P bth
containing very different proportions of these two kinds of
seeds. There is a practical difficulty in ascertaining a seed's
128 STUDIES IN SEEDS AND FRUITS
impermeability in water before testing the amount of its water-
contents, and this difficulty is very apt to arise in dealing with
variable seeds, notably in the seeds of Poinciana regia, which
behave almost like permeable seeds.
It is to seeds like those of Cxsalpinia Sappan and Entada
polystachya, where we can with some confidence distinguish the
two types of seeds by their external characters before the
experiment, that we must appeal. In their case it is plainly
shown in the table that the seeds which imbibe in the broken
condition most water from the air are those which lose least
water in the oven, or, in other words, that the ultra-dryness of
impermeable leguminous seeds is simply a diminution in the
water-contents as compared with permeable seeds. Thus we
find for Ctesalpinia Sappan that when the seeds held about 14
per cent, of water they did not increase their weight when ex-
posed in a broken state to the air. On the other hand, when
their water-contents amounted to less than 10 per cent, they
increased their weight about 9 per cent, by abstracting water
from the air. Similar results were obtained for Entada
polystachya. Thus :
(Seeds with 14 per cent, of water merely behave hygro-
scopically when broken.
Seeds with 9-7 per cent, of water add 9 per cent, to their
weight when broken.
Seeds with 10 per cent, of water add 1-6 per cent, to their
Entada weight when broken.
polystachya Seeds with 6 per cent, of water add 9-4 per cent, to their
weight when broken.
The data given in the table for permeable seeds of other
than leguminous plants are interesting, as they illustrate the
fact that many permeable seeds may hold as little water as some
of the impermeable leguminous seeds. This is particularly
clear when we distinguish between the coats and the kernel,
as is done in the table. Here we find that the kernels of
permeable seeds like those of Citrus, Hura, etc., may hold less
than 9 per cent, of water. Doubtless the presence of oil goes
ADDITIONAL EVIDENCE 129
to explain this low water-percentage ; but at all events this
fact shows how necessary it was to avoid comparing seeds
of different families when connecting impermeability with
diminished water-contents.
I come now to the additional evidence in support of the Further
principle typified by Guilandina bonducella in Chapter IV, that show^hatin
the seed-coverings of impermeable seeds possess the same
quality of ultra-dryness as the kernel, though often in a coverings
somewhat diminished degree, and the same quality of supply- same quality
ing the deficiency by absorbing water from the air, the ness as'thJ"
larger water-percentage of the coats being usually associated kernel -
with a diminished absorptive capacity of the freshly exposed
material.
Most of my results are given in the table a few pages
later ; but I will confine the discussion as before to legu-
minous impermeable seeds. All the kinds of seeds there
tested possess this quality of ultra-dryness for the coats as
well as the kernel, though the presence of oil in the kernel
of Adenanthera pavonina somewhat alters the regime. Most of
the results represent the average of three or four or more
experiments, the absorptive capacity in air and the water-
percentage being determined independently. In spite of
possible disturbing effects, due to variation in the seeds
and in the atmospheric conditions, the data thus obtained
go fairly well together. But in two cases, those of Guilandina
bonducella and Entada scandens, this disturbing influence was
removed by a simple expedient ; and these experiments have
been specially added to the others, since they are not only
the most critical but the most decisive. With Guilandina
bonducella the coats and kernel of each seed were divided
between two samples, so that the water-percentage and the
absorptive capacity in air were simultaneously determined
from similar examples. With Entada scandens the two
samples of the seed-coverings and the two samples of the
kernel were obtained from one large seed weighing about
500 grains. They gave the following results for the water-
9
130
STUDIES IN SEEDS AND FRUITS
Additional
evidence to
show that
the absorp-
tive quality
of broken
impermeable
seeds is not
affected by
exposure to
a tempera-
ture of 100*
C. whether
in the case of
the coats or
of the kernel.
percentage and for the fresh materials exposed to the air in a
broken condition :
' Coats hold 7-6 per cent, of water and gain in weight
Guilandina 1 2 per cent.
bonducella ' Kernels hold 4-2 per cent, of water and gain in weight
1 6 per cent.
Coats hold 13-8 per cent, of water and gain in weight
Entada 8 per cent.
scandens Kernels hold 7-5 per cent, of water and gain in weight
12 per cent.
These two seeds illustrate what is shown by other im-
permeable seeds in the table, namely, that the smaller absorptive
capacity of the seed's coats is associated with a larger water-per-
centage as compared with the kernel. Dioclea reflexa is irregular,
however, in this respect. But the behaviour of variable seeds
containing a good proportion of impermeable seeds supports the
same conclusion. This is shown in the table by samples of seeds of
Gesalpinia Sappan, Entadapolystachya, and two species otErythrina.
In Chapter IV I have already referred to the circumstance
that the capacity possessed by impermeable leguminous seeds
of considerably increasing their weight when exposed in the
broken condition to the air is but little affected by first sub-
jecting the materials to a temperature of 100 C. for an hour
or two. In that chapter I took the seeds of Guilandina
bonducella as a type. Here I will discuss the additional evidence
for impermeable seeds of the same order.
This double capacity was disclosed in a large number of
experiments on impermeable leguminous seeds. In the table
I have compared the two results obtained for seeds in the broken
condition. In one column we have the gain in weight by ab-
stracting moisture from the air when the materials are not heated.
In another column we have the gain after the materials have been
exposed to a temperature of 100 C. Many of the experiments
on the absorptive capacity of the unheated and heated materials
were carried out on different samples and under different climatic
conditions, so that disturbing influences were likely to affect
ADDITIONAL EVIDENCE 131
them, and a very close approximation between the two absorp-
tions could not often be looked for. However, in the main,
these independent experiments confirm the principle indicated by
the seeds of Guilandina bonducella^ that exposure to a temperature
of 1 00 C. does not seriously affect the absorptive capacity.
But to eliminate such disturbing conditions I made critical
experiments on certain impermeable seeds in which the absorp-
tive qualities of the unheated and heated materials were simul-
taneously tested in similar samples. The seeds in question were
those of Entada scandens, Erylhrina indica^ and Guilandina bondu-
cella. In the case of Entada scandens, one large seed weighing
nearly 500 grains supplied all the material for the double experi-
ment. In the cases of the two last named, each seed was divided
between the two samples, the one for exposure without heat to
the air, the other for exposure to the air after being subjected
to a temperature of 100 C. The results were as follows :
A. Entada scandens
Gain of coats and kernel: unheated, 10-8 per cent.; after 100
C., 9-5 per cent.
Gain of coats alone : unheated, 8-2 per cent. ; after 100 C., 8-0
per cent.
Gain of kernels alone : unheated, 12-3 per cent. ; after 100 C.,
IO'4 per cent.
B. Guilandina bonducella
Gain of coats and kernel: unheated, 13-7 per cent.; after 100
C., 14-2 per cent.
Gain of coats alone : unheated, 12*0 per cent. ; after 100 C.,
13-3 per cent.
Gain of kernel alone : unheated, 16-2 per cent. ; after 100 C.,
15-5 per cent.
C. Erythrina indica (impermeable seeds only selected)
Gain of coats and kernel : unheated, 4-5 per cent. ; after 100 C.,
3-4 per cent.
Gain of coats alone : unheated, 2-3 per cent. ; after 100 C., 1-6
per cent.
Gain of kernel alone : unheated, 5-0 per cent. ; after 100 C., 4-1
per cent.
1 32 STUDIES IN SEEDS AND FRUITS
From these similar samples we learn that as a rule exposure
to a temperature of 100 C. for from i^ to 2 hours but little
affected the capacities of either the seed-coverings or the
kernel for increasing their weight by absorbing moisture
from the air in the broken condition. It is scarcely worth
while to labour this point. The same indications are supplied
in the case of other impermeable seeds mentioned in the table,
such as those of Dioclea reflexa, Guilandlna bonduc^ Mucuna
urens, etc., and by the samples of variable seeds where im-
permeable seeds predominated, such as those of Ctesalpinia
Sappan, Erythrina corallodendron, etc.
The be- Coming to permeable seeds of the leguminous type, we
permeable notice in the table that during the period of five days
seeds. following the exposure to a temperature of 100 C., they
all regained from the air most of the water lost in the oven.
That they failed to return to the original weight is doubtless
to be attributed to the limited duration of their exposure
to the air, since it is clearly shown in the instances of Faba
vulgaris, Phaseolus multiflorus, and Pisum sativum on p. 142 that
if the test had covered a period of a week or two instead of
only five days, the seeds would have regained their original
weight. But they would not have displayed any excess,
except such as is included in the ordinary hygroscopic varia-
tion of about 3 per cent., and this is the great point of
contrast between permeable and impermeable seeds.
As respecting permeable seeds other than those of the
Leguminosae, the data for several kinds given in the table tell
much the same story. After exposure to the same tempera-
ture of 1 00 C., they in most cases regained much of their
lost weight by taking up water from the air, and, no doubt, if
the test had been prolonged, they would have regained all.
The behaviour of the seed-coverings of the Shaddock (Citrus
decumana] is abnormal, but I can throw no light on it here.
However, taking all the data for permeable seeds given in
the table, it is evident that whether leguminous or otherwise,
they as a general rule behave in the same way after being
ADDITIONAL EVIDENCE 133
exposed to a temperature of 100 C. in the broken or divided
condition. In five days they regain most of the weight lost,
and in a week or two they would regain all, maintaining their
original weight subject to ordinary hygroscopic variation.
When comparing the absorptive capacities of permeable Theabsorp-
and impermeable seeds it is requisite that the drying and dtfes of*'
shrinking process should be complete. In all these experi- th^dnSg
ments only seeds were employed that had accomplished the process has
not been
drying process and had attained a stable weight. If we place completed.
in the oven a seed that has not yet begun to dry, or has not
yet completed that process, we meet with a very different
behaviour. A bared fresh Horse-chestnut seed (Msculus)
cut up in slices, that had had its weight reduced in the oven
from 100 to 52 grains, increased its weight by only 7 grains
(52 + 7) during eight days. In the same way the seed of a
fresh Acorn (Quercus Robur\ after its weight had been reduced
in the oven from 100 to 58 grains, added only 4 grains to its
weight during an exposure to the air of eight days. A broken
seed of Dioc/ea reflexa which had not completed the drying
process lost 20 per cent, of its weight in the oven, and after
five days was still 5 per cent, short of its original weight.
On the other hand, normal resting seeds of the same plant,
which lost 8 '6 per cent, of their weight in the oven, behaved
like typical impermeable seeds during an exposure of five days
to the air, increasing their original weight by 9 per cent.
On the behaviour of seeds exposed to a temperature of
1 00 C. before they have commenced or before they have
completed the drying process, the principle of Berthelot,
discussed at length in Chapter VII, throws a flood of light.
The water which they subsequently regain from the air is
merely the water of hygroscopicity, which they would hold
whether living or dead. This amounts on the average to
only about 5 per cent, of the weight of the moist fresh seed
that has not begun to dry. Most seeds lose quite 50 per
cent, of their weight in the normal drying process, so that
there would be a large proportion of the water which a fresh
i 3 4 STUDIES IN SEEDS AND FRUITS
moist seed loses in the oven that it could never regain. Such
considerations render necessary a review of the general behaviour
of seeds after exposure to the oven test. It will be shown
in the following chapters that the whole problem can be
stated in quite a different manner if we introduce the principle
of Berthelot as a resolving factor.
Explanation The following table is intended to illustrate the contrast
ing tabe.^ " between impermeable and permeable seeds in their capacity
of increasing their weight by absorbing water from the air
when exposed in the broken condition, either with or without
a previous exposure to a temperature of 100 to 110 C.
It will be noticed that in impermeable seeds both the coats
and kernel possess this quality of adding considerably to their
weight when exposed unheated to the air ; whilst with perme-
able seeds both coats and kernel retain their weight, merely
displaying the normal hygroscopic variation of 2 or 3 per
cent., 98*5 to 101*5. Usually the inability to increase the
weight, except in the ordinary course of hygroscopic variation,
is indicated by 100. A previous exposure in the oven for
i^ or 2 hours does not materially affect the behaviour of
the seed or its parts. In the case of impermeable seeds
much the same excess weight is attained in about five days
after the oven test, whilst in permeable seeds the original
weight is more or less regained during the same period after
the heating ; and in those cases where there is a marked
failure to return to the original weight, it can be shown either
that the seed had not completed its drying process before the
experiment, or that the period of exposure to the air was too
short, a week or two being in their case required (see p. 142).
The behaviour of variable seeds is of course intermediate in
character. ..." Similar samples " used in certain experi-
ments were samples where each seed tested had been divided
between the two samples, so that truly mixed samples were
simultaneously experimented on. The same object was effected
in. the case of large seeds like those of Entada scandens (weighing
some 500 grains) by employing the same seed for both samples.
ADDITIONAL EVIDENCE
135
VJ .
^^
V
fH P~H
S S
H >-> <j
w a Ja
C " i oj
ft sj ' '
<u d, "> M*J
. x n j; v
1
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J js 1'S
. . ."a, . ."B. t>S
CJ fl) - *+" rH
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^Ci'I
in in 8 ^
* "- f, ~
TO TO O ^J
rz5 r^ *^ v
w5 w5 53
<u
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O ^~ O ^~oo n *^ O w
o ^ ~ g s " S3
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U
<*o O 1 ^i O O> t*i v> " " *A " * I O
O~O~OMM -O - ' -O
-S ,-3 ~ o g
^ v-^ rt* -5 K ^ ^ _C
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g^-o y, g 3 o a
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t^vo ONM m
^i ^ "^.S 1> -a O
a
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r< t^^O O oo M ro u^ tr^so w> ^ O
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IH r<i tf oo w rri^o o . . . . O
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rJvo^-OsOON vo O OOO
^
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V
fl JJ
a 1 ?
u .--,--__.--- ^g
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1 1 K*
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g M || = - | Ig
c,^g oo "]3 [n -5g''g
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TJ i fS ri'-^'-'-i M
136
STUDIES IN SEEDS AND FRUITS
C~ <u
; . 2 u u 3
-^ rt "Q. t/J.2
lllljs
CLcn U)
x u Hi ^
3 ^^ o
pi}'!' 8 d
D J3 g v O
lft? a l
fe^^g
' o ""a.
Mostly impermeable.
Hygroscopic in be-
haviour.
Most of sample perme-
able.
s s s s
, c - S -
^ 0- JJ D, ^
CL u (X > 91
s .u | ., | .
i^rti/) u^rtin 1^. rt
u
-S
6^ S
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"3 g rt 5
^ a u 2 s
p
: : : : o\
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o" : "o : : :
T3 ~- ^ .Q
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^^g u. ^2^,13
"^ 3 v2 rt C C
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- : ' ON
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ro O
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g.~-.a>
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w-i o * ^O ro oo
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c "" x S
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r_j *> v o
111
OS
p p ft p p
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1 I
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r*"* *4-
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ra m
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s s = = r =
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ADDITIONAL EVIDENCE
137
in
_CJ
>,
_tj ju -5
lete.
when quite
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ff |
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3 "3 5 bo i> c
3 .0 g ?>'i'|
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, , indica
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rt | g-|
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111 =11 s l 1*1 33 Ill^l
138 STUDIES IN SEEDS AND FRUITS
We have seen that the ultra-dryness of the kernel of an
impermeable seed is maintained through the impervious
character of its coats. In further illustration of the great
The resist- resistance which the seed is able to offer on account of its
by'imperme- impermeable coverings to the injurious influence of external
conditions, I will discuss the results of some experiments
atures. illustrating their behaviour under high temperatures. Although
none of the seeds germinated after exposure to a temperature
of 1 00 C., their behaviour under the test was very instructive ;
and it would seem that in no better way can the contrast
between permeable and impermeable seeds be shown than in
their modes of responding to different stages of heat.
It is of course natural that a seed-covering which is neither
As ex- hygroscopic nor pervious should have this influence. Yet
Ectada* * some very curious effects are produced when impermeable
scandensand seec [ s suc h as those of Entada scandens and of Guilandina
Guilandma
bonducella. bonducella, are exposed in an oven to a temperature of 100 to
110 C. They are well brought out in the accompanying
table, which contains the results of two simultaneous experi-
ments on these seeds ; and in order to emphasise the peculiarity
in the behaviour of the impermeable seed when heated with its
coats intact, I have added the results for the same seed when
subjected to a similar high temperature in the broken condition.
It is shown in the columns of this table that in their coats
these seeds behaved in a very similar fashion after an exposure
for two hours to a temperature of 1 00 to 1 1 o C. They lost
respectively 2*7 and 1-9 per cent, of their weight, the subsequent
efforts of both to supply the loss by absorbing water from the
air having a very slight result. Both of them then doggedly
resumed in their altered condition their previous im-
permeability, making no hygroscopic response to the variations
in atmospheric humidity and gaining back no weight on being
immersed in water. If we contrast this with their behaviour
when deprived of the protection of their coats (as indicated by
the average results of several experiments on other seeds of
the same species), we find that in the oven test they lost
ADDITIONAL EVIDENCE
RESULTS OF SIMULTANEOUS EXPOSURE FOR TWO HOURS TO A TEMPER-
ATURE OF I OO TO 110 C. OF ENTIRE SEEDS OF ENTADA SCANDENS AND
GUILANDINA BONDUCELLA, ILLUSTRATING THE POWERS OF RESISTING
HEAT IN THEIR SHELLS OR COVERINGS POSSESSED BY IMPERMEABLE
SEEDS, AS COMPARED WITH THE BEHAVIOUR OF THE SEEDS OF THE
SAME SPECIES EXPOSED TO THE SAME TEMPERATURE, BUT IN A
BROKEN CONDITION, AND THEREFORE NO LONGER PROTECTED BY
THEIR SHELLS.
(The results are stated in percentages, the materials tested being 2 entire seeds of
Entada scandens weighing in all 861 '3 grains, and 3 entire seeds of Guilandina bonducella
weighing io6'8 grains. The data given for the seeds in their broken condition represent
the average of a number of experiments made in other connections during the course of
this investigation. )
Changes in weight during and after the oven test.
Condi-
tion of
seeds.
Original
weight.
After
2 hours'
expos-
ure to
I 00 to
no C.
Weight after the oven test.
After
2 to 7
days' im-
mersion
n water.
M
*$
ft
N
M
3 months.
</>
1
a
f
Entire
in their
IOO
97'3
97*6
,7-6
97-6
97*6
97 -6
Entada
coats.
scandens |
In a
broken
IOO
88-6
99*0
104*6
104*5
103*0
....
1
condition
Entire
in their
IOO
98-1
98*4
9 8*4
98- 4
98*4
98*4
98-4
Guilandina 1
coats.
bonducella "j
In a
broken
IOO
92*0
IO5'O
111*5
111*4
106*0
i
condition
Entada scandens protected by its coats lost 2 '7 per cent, and regained 0*3.
,, unprotected ,, ,, 11*4 ,, ,, 16*0.
Guilandina bonducella protected ,, ,, 1*9 ,, ,, 0*3.
,, unprotected ,, 8'o 19-5.
1 1 -4 and 8-0 per cent, respectively. This was more than
regained after an exposure of some days to the air, there being
a final excess over the original weight of 4*6 per cent, in the
case of Entada scandens and of 11*5 per cent, in the case of
Guilandina bonducella.
Unfortunately, all the seeds failed to germinate, though
140 STUDIES IN SEEDS AND FRUITS
examination proved that their kernels were in appearance
sound. A more careful test of their germinative capacity
might have produced different results. However, the interest
of the experiment lies in its suggestiveness as to the mode in
which an impermeable seed might be able to resist a temperature
of 1 00 C. Provided that its water-contents are reduced to
a minimum, it could withstand even a greater amount of heat
and yet germinate. Becquerel, basing his opinion on the
experiments of Dixon, considered 120 C. as the limit for
desiccated seeds (Annales des Sciences Naturelles^ v., 1907).
With regard to my own results it may be added that the loss
of weight in the oven is not so surprising as the subsequent
resumption of impermeability. Behaviour somewhat similar,
though under different conditions, is noticed below in the
case of the impermeable seeds of another plant.
Another illustration of the method by which impervious
And by coats may enable seeds to resist high temperature was afforded
obtusifolia. by selected impermeable seeds of Canavalia obtusifolia under
the strain of a great variety of thermal conditions, both with
coats intact and with coats punctured, as shown in the diagram
below. Exposed to alternating dry and damp conditions at
ordinary temperatures and to extremes of dry and moist heat
in the oven, the seed with coats intact varied only about 1*2
per cent, of its weight during a period of seven weeks, whilst
the range of the weight of the seed with punctured coats
under the same tests and during the same period was 7-5 per
cent. But if we disregard the first loss of weight as concerned
with influences preceding the experiment, then the variation
under these highly contrasted conditions of the seed with
coats intact amounted only to 0*7 per cent., which is probably
not much greater than the variation that a quartz-pebble
would exhibit under the same circumstances. Since the
impermeable seeds of Canavalia obtusifolia normally increase
their weight by 5 or 6 per cent, when exposed to the air bared
of their coats, some proportion of the great variation displayed
by the punctured seeds must be ascribed to their original
ADDITIONAL EVIDENCE
141
DIAGRAM ILLUSTRATING THE DIFFERENT BEHAVIOURS UNDER A GREAT
VARIETY OF CONDITIONS OF INTACT AND PUNCTURED SEEDS OF
CANAVALIA OBTUSIFOLIA OF THE IMPERMEABLE TYPE.
(The experiment extended continuously from August 14 to October i, and was
carried out in England.)
Grains.
Warm, dry air in
cupboard, temp.
7-7S F.
Cool, damp
air in
room, temp.
bo'-f>s' ?
Ten
hours'
dry heat
in oven,
temp.
85-
105" F.
Cool, damp air
in room, temp.
60-65 E.
Three
hours'
moist
heat in
oven,
temp.
ISOF.
Cool,
damp
air in
room,
temp.
60" F.
One
hour in
steam,
temp.
2 1 2 F.
Cool,
damp
air in
room,
temp.
60 F.
Aug. 14
Aug. 19
Sept. 6
Sept. 14
Sept. 14
Sept. 1 6
Sept. 1 8
Sepc. 1 8
Sept. 28
Sept. 28
Oct i
Grains.
109
109
108
108
107
,..'
P
jnctured
107
1 06
1 06
105
Intact
105
104
&;
/
/
104
103
C S
~f **
...-'
"~~~^
-?--
''
*
' Intact
103
101
/
\ /
102
IOI
\
IOI
too
IOO
99
99
98
98
In one case the seed-coats were punctured in several places.
In the other case the coats were left intact.
Nine or ten seeds were employed in each experiment.
The first fall in weight was due to the seeds having been previously kept under less
dry conditions, the small loss in the case of the seeds with coats intact being probably
connected with tissue adherent to the scar. The loss in weight of the punctured seeds on
September 18 after being exposed for three hours to moist air in the oven at a temperature
of 150 F. is remarkable. The punctured seeds here displayed a caving-in or collapse of
their coverings around each puncture. A vessel of water was placed in the oven during
the test, and after cooling down the inside of the oven was covered with moisture.
ultra-dry ness. None of the seeds germinated at the close of
the experiment, a negative fact which probably depends as
142
STUDIES IN SEEDS AND FRUITS
much on the imperfection of the method as on the failure of
the seeds, since, as above remarked, experiment has established
the ability of certain seeds to withstand for some hours a
temperature of 100 to 120 C. However, the original
purpose of this experiment has been served in demonstrating
the protection an impervious covering affords against extreme
thermal and hygrometric conditions.
Very different is the behaviour of the permeable seed
under the strain of a high temperature, a difference which its
The be- hygroscopicity would lead one to expect. Permeable seeds
permeable give up their moisture in the oven almost as readily when
seeds under^ protected by their coverings as in the exposed condition.
ature. Since we have already seen in the chapter on type seeds that
with such seeds the coats merely restrain but do not prevent
the hygroscopic reaction of the kernel, the results given below
are such as we should have looked for.
TABLE SHOWING THE INFLUENCE OF THEIR COVERINGS ON THE BEHAVIOUR
OF PERMEABLE SEEDS WHEN EXPOSED FOR TWO HOURS TO A TEMPER-
ATURE OF 100 TO no" C.
(Two samples of each kind of seed were employed, one with the seeds entire, the
other with the seeds cut across so as to be deprived of the protection of their coverings.
The seeds were eight or nine months old, the samples of the peas weighing 100 grains
and of the others 200 grains. The results are given in percentages. )
Condition.
Original
weight.
Weight
after the
oven test.
Loss in
the oven.
Time occupied
in regaining
original weight.
Faba vulgaris (
Entire
IOO
90*0
10 "0
6 weeks
(Broad Bean) 1
Cut across
IOO
86-1
13-9
2 ,,
P i s u m sat i vum (
Entire
IOO
88-8
1 1 '2
2
(Peas) J
Cut across
IOO
85-9
I4-I
i week
Phaseolus multi- f
florus (Scarlet--!
runner) (_
Entire
Cut across
IOO
IOO
89*2
84-9
io'8
15-1
6 weeks
2
By contrasting the results above tabulated with those given
a few pages back for Entada scandens and Guilandina bonducella^
where the seeds were exposed to the same test, we can frame
a numerical estimate of the difference in the degree of protec-
tion against high temperatures which the coverings offer in the
ADDITIONAL EVIDENCE 143
case of permeable and impermeable seeds. Thus, assuming
that the seed gave up approximately all its water when deprived
of the protection of its coats, then the permeable seeds entire
in their coverings may be regarded as having lost as much as
from 70 to 80 per cent, of their water-contents, whilst the im-
permeable seeds in the same entire condition and exposed to
precisely the same test lost barely 25 per cent.
Further contrasts in the behaviour of permeable and im-
permeable seeds when exposed in their coats to a temperature
of 1 00 to 1 10 C. for two hours are exhibited when we compare
the results of their efforts to regain the lost water from the
air. With impermeable seeds we have seen that very little
effort is made to gain back their original weight, and that after
the oven test they resume their impervious character, doggedly
refusing to make any response to the hygrometric changes of
the air and adding nothing to their weight when immersed in
water. On the other hand, after the oven test permeable seeds
slowly regained the water lost, but so very slowly that six weeks
in the cases of Faba vulgaris and Phaseolus multiflorus and two
weeks in the case of Pisum sativum were occupied in returning
to their original weight. The influence of the coats is especially
brought out in the case of the two types of seeds, if we regard
their behaviour when the seed is broken up and is thus deprived
of the protection of its coats. After the oven test the imper-
meable seed gains back in a few days all the water lost and a
considerable percentage (5 to 10 per cent.) more ; whilst the
permeable seed returns to its original weight in a week or two,
and is subject then to only the normal hygroscopic variations.
The differences in the nature of the protection afforded by Summing: up
the coats of permeable and impermeable seeds when exposed for nces in the"
two hours to a temperature of 100 to 110 C. may be thus b |rmeSSe f
briefly stated. In the impermeable seed the coats only allow and imper-
one-fourth of the water-contents to escape, and by subsequently when ex-
resuming their imperviousness practically frustrate the seed's
effort to gain back the loss. In the permeable seed the in- tempera-
hibitive influence of the coats is so slight that three-fourths of
i 4 4 STUDIES IN SEEDS AND FRUITS
the water-contents are lost in the oven ; whilst the seed's
attempt to regain from the air the water lost is retarded, but
not prevented, the original weight being in time attained.
The retardation in the process of re-absorption is, however,
very marked, since in the Broad Bean and Scarlet-runner the
period is extended from two to six weeks and in the Pea from
one to two weeks.
There are several points raised in the foregoing remarks
which will be elucidated in the chapter on Hygroscopicity,
notably, that concerned with the return of permeable seeds to
their original weight after being heated. Only completely air-
dry seeds would thus behave, since seeds that are still drying
would fall considerably short of the weight they possessed
before being placed in the oven.
SUMMARY
(1) This chapter contains the bulk of the data on which are
based the distinctions in behaviour between permeable and impermeable
seeds, which are described and illustrated by typical examples in
Chapter IV.
(2) The capacity of increasing their weight considerably by absorb-
ing moisture from the air, when impermeable seeds are deprived of
the protection of their coats, is confirmed by the results of ex-
periments on the seeds of other plants. Other results also go to
confirm the conclusion drawn for type seeds in Chapter IV, that the
gain in weight is far more rapid when the kernel is completely bared
than when the coats are merely punctured. The average results of all
experiments on this absorptive capacity of impermeable seeds are
tabulated j and it is generally concluded that leguminous seeds of this
type when deprived of the protection of their coverings as a rule
increase their weight between 5 and 10 per cent, in a few days
(P- "5).
(3) The indications, though limited, go to show that impermeable
seeds retain their ultra-dryness for a number of years (p. 119).
(4) The data show that the capacity of absorbing water from the
air when' an impermeable seed is bared of its coats is greater in the
tropics than in temperate climates, and that the gain in weight is
maintained longer when it is acquired slowly, as in filed seeds, than it
is when acquired rapidly, as in bared kernels (p. 1 20).
ADDITIONAL EVIDENCE 145
(5) The results for variable seeds (permeable and impermeable seeds
in the same plant) of baring the kernel, or exposing it by cutting it
in halves in its coats, are also tabulated ; and it is shown respecting
their relations with the moisture of the air (a) that the permeable seeds
behave hygroscopically, like ordinary seeds of the type ; (b] that imper-
meable seeds behave also like seeds of their type and add considerably
to their weight ; (c] that mixed samples of the two types of seeds
display intermediate qualities (p. 122).
(6) Additional data are given concerning the behaviour of bared
permeable seeds that have completed their drying in air ; and it is
shown, as in Chapter IV, that the main result is to give a rather
freer play to the hygroscopic reaction, the average weight remaining
about the same (p. 124).
(7) Further evidence is then supplied of the association of the ultra-
dryness of impermeable seeds with a low water-percentage, and in the
first place the necessity of restricting the inquiry to seeds of the same
order is pointed out.
(8) Thus with leguminous seeds we obtain the following general
results for seeds broken up or cut open and exposed to the air :
Impermeable seeds holding 7-5 per cent, of water add 9-2 per cent,
to their weight.
Impermeable seeds holding 11-7 per cent, of water add 5*0 per cent.
to their weight.
Permeable seeds holding 15-0 per cent of water add o-o, behaving
hygroscopically.
(9) The indications of this rough estimate are confirmed by the
results of experiments on seeds where both the permeable and imper-
meable types of seeds are produced by the same plant.
(10) More evidence is adduced to show that in impermeable
seeds the seed-coats possess the same quality of ultra-dryness as the
kernel.
(n) Additional data are given in support of the conclusion that
the capacity possessed by impermeable seeds of considerably adding to
their weight when exposed to the air in a broken state is not affected
by first exposing the materials to a temperature of 100 C., whether in
the case of the coats or of the kernel.
(12) Permeable seeds in this respect present a great contrast to
impermeable seeds, since in a week or two they gain back from the
air only the water lost in the oven and assume a stable weight subject
merely to ordinary hygroscopic variation.
(13) In the case of both permeable and impermeable seeds it is
necessary, when comparing their absorptive capacities after heating, to
employ only seeds that have completed the drying and shrinking
process, since seeds of either type, when incompletely dried, fail to
IO
146 STUDIES IN SEEDS AND FRUITS
return to their original weight. On this point the principle of
Berthelot, discussed in Chapter VII, throws a flood of light.
(14) The contrast between impermeable and permeable seeds is
further illustrated by their different modes of responding to high
temperatures under the protection of their coats. Whilst impermeable
seeds, when exposed for two hours to a temperature of 100 to I io c C.,
lose only about 25 per cent, of their water-contents, permeable seeds
that have completed their drying in air lose under these conditions in
the oven as much as 75 per cent. (p. 138).
(15) But the contrast is extended when we compare the results of
their efforts to regain from the air the water lost in the oven. The
impermeable seed makes a very slight effort in this direction ; and
whilst its coats quickly resume their impervious character, the seed
doggedly refuses to make any response to the variations in the
atmospheric humidity and adds nothing to its weight when placed in
water. On the other hand, after the oven test the permeable seed
slowly regains from the air the water lost, but so gradually that weeks
are taken up in the process, the original weight being ultimately
attained subject to the ordinary hygroscopic reaction. The return of
the air-dried permeable seed to its original weight after the heat test is
a point of importance, since seeds that have not completed their drying
in air fail to reach their original weight, a critical distinction discussed
in detail in the chapter on Hygroscopicity (p. 139).
(16) The great resistance which a seed protected by impermeable
coats is able to ofter to extremes of moist and dry heat ranging up to
1 00 C., and to alternating dry and damp conditions, is shown in the
behaviour of impermeable seeds of Canavalia obtusifolia. Kept under
the strain of a great variety of extreme conditions for seven weeks,
seeds with coats intact did not vary i per cent, in weight, whilst those
with punctured coats varied as much as 7-5 per cent. (p. 140).
CHAPTER VII
f
HYGROSCOPICITY
HYGROSCOPICITY in a seed may be defined as the variation of Definition of
its water-contents in response to the changes in the hygrometric scopicity.
state of the atmosphere, such a variation being due to its
property of readily imbibing moisture from the air and as readily
parting with it. This interesting quality, which is characteristic
of all vegetable substances and of much besides, has in recent
times been studied by numerous investigators, including
amongst others Jodin (1897), Berthelot (1903), Leo Errera
(1906), Becquerel (1907), and Demoussy (1907), the years in-
dicating the date of publication of the author's paper consulted.
The most comprehensive treatment of the subject is to be
found in the memoir of Leo Errera entitled " Sur 1'Hygrosco-
picite comme cause de 1'action physiologique a distance "
(Recueil de I'lnstitut Botanique Leo Errera^ Universiti de Bruxelles,
tome vi., 1906). Assisted by the previous researches of Classifica-
Warburg and Ihmori, he was able to direct attention to certain different
principles involved and to show that hygroscopicity in its
widest sense has a far more extended significance than is
generally imagined, as is sufficiently brought out in his
classification of the various forms of this property, both
physical and chemical, which I have reproduced in Note 9 of
the Appendix. The matter as here dealt with appeals mainly
to the physicist and the chemist ; but it is essential, before
studying hygroscopicity as affecting plants, to bear in mind the
broad treatment of the subject which gives so much importance
147
148 STUDIES IN SEEDS AND FRUITS
to this paper. Hygroscopicity is there exhibited in the most
comprehensive sense, as displayed (a) in the condensation of
the water-vapour of the air on the cold surface of a glass ;
(^) in the capillarity of hair, wool, cotton, wood shavings, etc. ;
(<:) in the imbibition of water from the air by gelatine ; (d] in
the deliquescence of common salt ; (e) in the absorption of
water from the air by concentrated sulphuric acid ; and (/)
in the behaviour of quicklime. Becquerel, in applying this
classification to seeds, suggests two kinds of hygroscopicity :
(1) physical, where condensation is affected by the cold, smooth
sides of the seed or by the walls of very fine capillary pores ;
(2) chemical, when induced by the affinity of certain substances
for water (Annales des Sciences Naturelles Botanique, tome v., 1 907).
Coming to the display of this quality by vegetable materials
in general, I will, before handling my own observations, take
my cue from the researches of Jodin on peas, and will then
look to the principle laid down by Berthelot for guidance in
the search after the significance of hygroscopicity in plant-
tissues. But it is necessary to preface my remarks by point-
ing out that the hygroscopic reaction understood by these
investigators, and always intended in these pages, is the
response of the permeable seed (by absorbing or yielding up
water-vapour) to the varying hygrometric condition of the air,
a never ceasing " give and take " process by which the
equilibrium between the seed and the air is maintained.
Theobserva- Jodin approached the subject from the biological and
Jodin'on Berthelot from the physical side, and both arrived at the same
peas. conclusion, that we are concerned with a quality that is inde-
pendent of life. Jodin, in his paper published in the Annales
Agronomiques for October 1897, tells us that living and dead
peas (those recently grown and those that had long lost their
germinative capacity) exhibited much the same hygrometric
variation in the course of a year's exposure to ordinary air-
conditions. Stated as a percentage of the average weight of
the air-dry resting seed, his results give a variation for the live
peas of 8 to 23 per cent., and for the dead peas of n to 21
HYGROSCOPICITY 149
per cent. It was the work of Jodin that led Becquerel in the
paper before quoted to make the critical distinction in a seed's
water-contents between the water of hygroscopicity and the
water concerned in the latent life of the embryo.
Whilst several years have passed since Jodin directed his
attention to the ordinary hygrometric variations experienced
by peas, Berthelot in more recent times has opened up the
whole subject of the hydratation of vegetable matter, and in
so doing has thrown an important light on the nature of
hygroscopicity in plants (" Recherches sur la desiccation des
plantes et des tissues vegetaux ; conditions d'equilibre et de
reversibilit6," Annales de Chimie et de Physique^ April 1903).
He shows that the peculiar property possessed by air-dried
vegetable matter of regaining from the air the water it has
been made to lose by heat and other artificial means is a
function of the hygrometric condition of the atmosphere. It
is not easy for me to state Berthelot' s principle tersely, and Berthelot's
" 1 t
accordingly I have above followed Maquenne in his reference reversibility,
to this subject in Comptes rendus^ October 1905. Nor is it easy
to grasp its full significance at first, since, as is natural in such
abstruse inquiries, much will seem pointless that does not cross
the boundary of one's own researches. To me perhaps it is
not so hard, since the principle has cast a flood of light upon
the results of my studies of permeable and impermeable seeds.
A plant, says Berthelot, does not dry entirely in air like
porcelain or metals (see Note 21 of Appendix). It retains
after being thus dried a certain amount of water, which varies
in response to the changes in the hygrometricity of the atmo-
sphere. When this water has been driven off by exposure to a its applica-
temperature of 110 C., it is gained back little by little from tissues ui a
the air up to a limit practically the same as that reached when & eneral -
the plant was dried in air. In a word, the water which the
air-dried material loses in the oven is regained in the air.
This is Berthelot's principle of reversibility, and it is
characterised by him as essentially a physico-chemical process
independent of life. It applies equally to the plant that has
1 5 o STUDIES IN SEEDS AND FRUITS
been dried in air, to the plant that has died spontaneously, and
to the plant that has been subjected to almost absolute desicca-
tion by heat and other means, all ultimately reaching the same
condition of equilibrium with regard to the atmosphere.
We will illustrate Berthelot's principle by combining in
one statement the results of his different experiments.
Portions of a living grass, a species of Festuca, weighing, we
will suppose, 100 grammes, are allowed to dry in the air of an
ordinary room for some days, until they acquire a stable weight
affected only by the usual small hygroscopic fluctuations.
Their weight is thus reduced by loss of water to about 66*5
grammes. They are then exposed to a temperature of no
C. for some hours, with the result that the weight is further
reduced to 61 grammes. After being laid aside for some days,
the material, by the absorption of moisture from the air, returns
to the original air-dried weight of about 66*5 grammes, and
there remains, varying slightly with the changing humidity of
the atmosphere. It is in the 5^ grammes which the air-dried
material lost in the oven and regained when subsequently
exposed to the air that the secret of the hygroscopicity of
plants lies.
TABLE ILLUSTRATING BERTHELOT'S "PRINCIPLE OF REVERSIBILITY."
(THE RESULTS OF DIFFERENT EXPERIMENTS ARE HERE COMBINED,
THE MATERIALS EMPLOYED BEING PORTIONS OF A SPECIES OF
FESTUCA.)
Weight in grammes under different conditions.
Fresh weight.
Dried in air
of an ordi-
nary room.
Died spon-
taneously.
After exposure
to temperature
of 110 C.
After a subsequent
exposure of some
days in the air of
an ordinary room.
IOO
IOO
IOO
66 '5
66-5
61
61
61
66-5
66-5
66-5
Note. The data representing the effect of exposing fresh and air-dried material to a
temperature of 110 C. belong to the same experiment, the rest of the data being supplied
from the indications of other experiments.
HYGROSCOPICITY 1 5 1
The feature in this table which will prove to be of
the greatest significance to us, in respect to the behaviour
of impermeable seeds when exposed to the air, is that
which shows that the water regained from the air, after
fresh plant-tissues have been exposed to a temperature
of 1 00 to 110 C., is the water of the dead plant and of
the plant dried in the air, and is therefore independent of
vitality.
In the above table I have pieced together the indications
of different experiments in order to emphasise certain points
in the behaviour of plants when exposed to natural and artificial
desiccation. After reading Berthelot's paper I experimented
on some fresh leaves of the Hazel (Cory /us Avellana), with the Thetesti-
results below given. His principle is well illustrated there, Hazel f
and we can see at a glance that the water which the fresh leaves leaves '
gained back from the air after being exposed to a temperature
of 105 C. is the water which they would have contained as
ordinary air-dried leaves. For about three years I have been
EXPERIMENTS BY THE AUTHOR ON FRESH HAZEL (CORYLUS AVELLANA)
LEAVES IN ILLUSTRATION OF BERTHELOT'S " PRINCIPLE OF
REVERSIBILITY."
Results of the drying and heating tests.
The water of hygroscopicity.
Fresh
weight.
After dry-
ing in air
of room.
After ex-
posure to
temperature
of 105" C.
in oven.
Three or
four days
after the
oven test.
Lost in
oven after
drying
in air.
Gain in
air after
the oven
test.
Stated as
a per-
centage
of the
dry weight.
A
B
C
D
IOO
IOO
IOO
IOO
3 I- 3
32-*
28-0
29-4
31-0
29*6
3!'4
33'o
34'5
3 2 '9
3 '3
3 '4
3 '4
3'6
3'S
3'3
I2'I
1 2 "2
11-3
ii'i
Hundred -grain samples of the fresh material were used. In the case of experiments
A and B, the sample was first dried in air for about five days, when it reached a stable
weight. It was then subjected to a temperature of 105 C. for i| hours, and afterwards
left exposed to the air of the room for three or four days, when it ceased to gain weight.
In the case of experiments C and D the fresh materials were placed in the oven without
previous drying in air.
152 STUDIES IN SEEDS AND FRUITS
putting this question to myself as to the significance of the
gain in weight of plant-tissues, and more particularly of seeds
after being exposed to desiccation in the oven, never dreaming
that such a simple experiment would supply the answer. To
have been contented with attributing it to hygroscopicity would
have explained little. As a disconnected fact it appeared
without interest and without meaning. What was required
was the establishment of a relation between this property and
some other attribute of plant-tissues ; and this 1 ultimately
found in the principle of Berthelot.
From this standpoint the water-contents of plants could be
divided into two parts, the water of hygroscopicity and the
Berthelot's water of vitality. The first, being independent of life, is
anguishes ^ equally characteristic of the plant living and the plant dead.
h h gro- ter f ** * s t* 16 residuum left in the air-dried material ; and it is the
scopicity water that the same material loses in the oven and regains
from the . i 1 i i- i i
water of in the air. 1 he second is the water that distinguishes the
vl iy ' plant as a living organism. Its quantity is regulated only
by the needs -of that organism. Unlike the water of hygro-
scopicity, it does not directly respond in its variations to
the hygrometricity of the air. On the other hand, hygro-
scopicity being a non-vital process represents the response of
the non-vital part of a plant's water-contents to the varying
humidity of the atmosphere. We can thus understand
how the residuum of water in the air-dried plant is the
water that represents a function of the hygrometric state of
the air.
This mode of differentiating the water-contents of plant-
tissues is of practical importance. There are many ways of
stating the proportions, and I have spent much time in trying
to harmonise them with the results of my observations.
The simplest Finally, it became evident that of the numerous methods of
stating the describing the " hydratation " of plants there were none so
simple and none so true as that implied in the principle of
plant-tissues. Berthelot. There is the water that the organised tissues
contain, whether living or dead, the water of hygroscopicity ;
HYGROSCOPICITY
'53
and there is the water which they hold only as living structures,
the water of vitality. The chemist, when producing by
synthesis organic vegetable matter, would allow the atmosphere
to supply the water of hygroscopicity, whilst he himself in his
creative role would have to supply the water of vitality. This
in a sense is very much what a baker does when he adds water
to his flour in making bread. As shown below, bread behaves
like fresh plant-tissues when dried in air and when desiccated
by heat. The water it regains from the air after heating is
the water originally existing in the flour as supplied by the
miller, and the water it does not gain back is what the baker
put into it.
EXPERIMENTS BY THE AUTHOR ON IOO-GRAIN SAMPLES OF BREAD IN
ILLUSTRATION OF BERTHELOT'S " PRINCIPLE OF REVERSIBILITY."
Treatment
of samples.
Results of the drying and heating tests.
The water of hygroscopicity.
Original
weight.
After
drying in
air of
room.
After
exposure to
temperature
of 105 C. in
oven for
ij hours.
Three or
four days
after the
oven test.
Lost in
oven
after dry-
ing in air.
Gain in
air after
oven test.
Stated as
a per-
centage
of the dry
weight.
Dried in air
and then
IOO
70-3
6l'2
70-4
9' 1
9-2
15-0
placed in
oven
Placed at
IOO
60*5
70*0
9'5
'57
once in
oven
Divided into small squares, the bread occupied about six days in reaching a stable
weight in air before being placed in the oven, where it was kept for i hours. Three to
four days were passed in acquiring a stable weight after the oven test.
When we come to apply the test of experiment to this The same
principle as it affects seeds, we get the same indications. The fnistrated in
simple experiment of drying a fresh seed first under ordinary
air-conditions, then in the oven at 100 to no C., and after- seed,
wards allowing it to remain exposed to the air for a few days
until it assumes a stable weight, supplies results that make the
The implica-
tions of
Berthelot's
principle.
STUDIES IN SEEDS AND FRUITS
statement of a seed's water-contents as easy as it was difficult.
All my results on the varying water-percentages of seeds, and
on the capacity of regaining from the air the water lost in the
oven, arrange themselves in an intelligible system in the light
of the principle below typified in the behaviour of the full-
grown, moist pre-resting seeds of Phaseolus multiflorus. The
hydratation of these seeds in this condition of active vitality
may be thus stated :
Water of vitality .
Water of hygroscopicity
Solids .
64-8
5'2
30-0
lOO'O
THE PRINCIPLE OF BERTHELOT ILLUSTRATED BY THE BEHAVIOUR OF
THE FULL-GROWN UNRIPE OR PRE-RESTING SEEDS OF PHASEOLUS
MULTIFLORUS. (Three seeds weighing 140 grains were experi-
mented on by the author ; the results are given as percentages.)
Results of the drying and heating tests.
The water of hygroscopicity.
After
Unripe or
pre-rest-
ing seed
from the
green pod.
After
drying in
air of room.
exposure to
a temperature
of 105 to
110 C. in
oven for
2 hours.
Six or seven
days after
the oven test.
Lost in
the oven
after dry-
ing in air.
Gain in air
after the
oven test.
Stated as
a per-
centage of
the dry
weight.
IOO
35'3
30 'o
35 -o
S'3
S'o
X 7*3
Important as the principle of Berthelot is in the differen-
tiation of the water-contents of plant-tissues generally, its
application is still more interesting in its results in the case of
the hydratation of seeds. It not only enables us to recognise
in clear outlines the nature of the contrast between permeable
and impermeable seeds ; but this implication supplies quite a
novel way of viewing the problem of the latent life of seeds.
If the implication is valid, its influence on our views should be
revolutionary.
HYGROSCOPICITY 155
In the first place, as regards the contrast between (a) That air-
permeable and impermeable seeds, it is evident that an seeds^both
air-dry permeable resting seed, which has assumed a stable peccable
* . * and imper-
weight, subject only to ordinary hygroscopic variations, meable, con-
i .u r i 111 tain only the
contains only the water or hygroscopicity, and that the water of
water of vitality disappeared in the drying process. It scopiciity-
also becomes apparent that the impermeable seed con-
tains only the water of hygroscopicity, but in a diminished
amount, so that when deprived of the protection of its
impermeable coverings it at once begins to supply the deficit
by abstracting moisture from the air until a stable weight is
reached.
The implication of course is that resting seeds completely
air-dried, whether permeable or impermeable, possess only
the water which is independent of vitality. If Berthelot's
principle is true and the implication is valid, there is in the
typical resting seed no water that is associated with any vital
function. (I am not here speaking of water locked up in
chemical combination in the seed's tissues, since that may be a
property of both living and dead matter.) Should the seed
exposed to a temperature of 100 C. in the oven yield up (6) that in
more water than it subsequently regains from the air, the higs^ds 8 *"
inference is that it had not completed its drying in air and the f e 1S no .
f T-I water associ-
still contained some of the water of vitality. This residuum ated with
of the water of vitality left in the deficiently air-dried function.
seed has nothing to do with the life of a resting seed,
but merely represents the remains of the water of the
large, soft pre-resting seed of the moist green fruit, a seed
that would have proceeded with its growth and with its
development into a young plant without any pause, if the
resting period had not been imposed on it through external
influences. The resting seed needs no water to prolong its
life, the presence of water being more likely to curtail its
existence than to endow it with longevity. Indeed, there
would seem to be more than fancy in the speculation of
M. Demoussy that a perfectly dry seed kept protected from
i 5 6
STUDIES IN SEEDS AND FRUITS
The view of
Becquerel.
Schroder's
experiments.
the air has the potentialities of immortality (Comptes rendus y
December 1907).
Yet it cannot be doubted that the view expressed so
clearly by Becquerel (Ann. des Sciences Nat. Botan., v., 1907),
that it is absolutely necessary to distinguish in a seed between
the hygrometric water that can vary and the water enclosed in
the cellules of the embryo and albumen which is invariable,
at present holds the field. We must distinguish, he says,
between the water of hygrometricity and the water that
plays a part in the phenomena of the latent life of the
seed. But if Berthelot's principle is correct, the only
water that a seed retains after it has completed its drying
in air is the water of hygrometricity. According to the
implications of this principle, the true resting seed, as
already observed, needs no water for the support of its
latent life ; and the latent life itself becomes almost a figure
of speech.
Several years ago SchrSder ascertained that grains of three
cereals (species of Hordeum and Triticum) retained their
germinative capacity, notwithstanding that after undergoing a
process of artificial desiccation for nearly three months their
water-contents had been reduced respectively to 0*5, fo, and
2'o per cent. (Untersuch. Bolan. Inst. zu Tubingen, 1886). It
would be quite as legitimate to infer from this experiment that
resting seeds can dispense with water altogether as to assume
that Schroder in his experiment reached the minimum com-
patible with the preservation of the germinative powers.
There is an obsession in the human mind respecting water and
active life that makes it difficult to assimilate the notion that
a resting seed could possibly do. without it. The standpoint
adopted in this chapter is that the occurrence of water in a
properly air-dried seed is accidental as far as it is concerned
with the retention of the germinative capacity. It could have
no concern for the student of the latent life of seeds, since its
quantity would be the same whether the seed be living or
dead.
HYGROSCOPIC1TY 1 57
Later investigations on the desiccation of seeds have been
numerous ; but many of them are summed up by Becquerel Becquerel on
in his paper on the latent life of seeds (Ann. Sci. Nat., 1907). seeds!* 1 *
There are certain seeds, he points out, which are able to resist
the most powerful desiccating agencies at our command ; and
very significant is his conclusion, after a review of the liquid-
air results, that it is the seed where the water and " gaz " have
been reduced to the narrowest possible limits by the most active
desiccators of the laboratory that best withstands these tests.
There seems no necessity to assign a function to the extremely
minute amount of water that might survive the desiccating
process.
On the contrary, it might be urged that its water is the Water is the
greatest foe to a seed's longevity. What, we may ask, is the toTseed's 6
real biological significance of the hygroscopicity of seeds, as lon evltv -
far as their longevity is concerned ? It is their hygroscopicity
that limits the life of permeable seeds ; or, in other words,
the constant reaction between the seed and its atmospheric Thehygro-
environment places a term to its existence. Not the least
interesting of the conclusions drawn by Jodin from his
observations on peas lies in this direction, and we may apply its absence
, , , . 1^1 favours their
it to permeable seeds in general. The continued hygroscopic longevity.
reaction, he points out, would in the course of time bring
about molecular changes in the seed, terminating in its loss of
germinative power and death. Thus we can perceive by
implication how the impermeable seed, by not responding to
the changes in its atmospheric surroundings, is secured against
one great risk to its longevity. Here, again, we perceive
that the long life of the seed presents itself as an affair of
the coats rather than one concerned with the dormancy
of the protoplasm of the embryo. It is the free play of
the hygroscopic reaction that curtails the life of a permeable
seed. It is the absence of this reaction that gives long life to
the impermeable seed.
After this long digression on the significance of hygro-
scopicity in seeds, 1 come to my own studies in this connection.
i 5 8
STUDIES IN SEEDS AND FRUITS
The author's
studies of
hygro-
scopicity in
seeds.
Permeable
seeds alone
are hygro-
scopic.
The hygro-
scopic range.
Its charac-
teristics.
Effect of
different
climates on
the weight
of the same
seed.
My observations on the hygroscopic behaviour of seeds are
naturally concerned only with permeable seeds, since the
impermeable seed in the usual sense of the word is non-hygro-
scopic, and when employed in experiments merely serves to
give contrast to the results. Hygroscopic seeds weighed daily
during a fortnight of changeable weather usually vary i^ or 2
per cent, of their average weight, an amount, however, which
is only about half of what may be regarded as the ordinary
extreme of the hygroscopic range, which, as ascertained by
a method to be subsequently described, is usually 3 or
4 per cent. This reaction figures as a possible disturbing
cause in all experiments on seeds where the balance is
employed.
Seeds as a rule continue to lose weight by drying during a
period varying from a few weeks to two or three months after
being gathered from the plant. If we extend the experiment
over a year or more, employing only seeds that have completed
the drying process and have acquired a stable weight, we find a
response to the varying humidity of the air not only in the
minor changes during short intervals, as between day and
night, and in the greater changes from week to week, but
also between the different seasons. It may here be remarked
that the seasonal changes in weight were well exemplified
in my experiments on the seed of sEsculus Hippocastanum
(Horse-chestnut). Seeds that had been kept for three years
were usually i or i^ per cent, heavier in the winter than in
the summer.
Reference will now be made to the changes of weight
which many seeds undergo in transference between regions
where different hygrometric regimes prevail, as between
tropical and temperate countries. I made some observa-
tions in this direction in the case of seeds taken from
England to Jamaica in November 1907, seeds which had
been gathered fresh in Jamaica in the spring of the same
year. Permeable, impermeable, and variable seeds were here
represented.
HYGROSCOPICITY
'59
TABLE ILLUSTRATING THE CHANGES IN WEIGHT EXPERIENCED BY
TROPICAL SEEDS WHEN TRANSFERRED FROM ENGLAND TO JAMAICA,
AND FROM JAMAICA BACK TO ENGLAND. (Seeds obtained fresh in
Jamaica in spring of 1907.)
Change stated
Weight in grains.
as a percentage
of the total weight.
Character.
Eng-
land,
Oct.
1907.
Jamaica,
Jan.
1908.
Eng-
land,
April
1908.
Rise.
Fall.
Range.
Canavalia ensiformis (7
Permeable
167-85
169*60
163-40
1*04
3-66
37
seeds ; Leguminosse)
Achras Sapota (10
Permeable
101-55
102*80
99*80
1*23
2-91
2-9
seeds ; Sapotacese ;
fruit baccate)
Chrysophyllum Cainito
Permeable
51-70
52-15
50-30
0*87
3*55
3-6
(4 seeds ; Sapotaceae ;
fruit baccate)
Abrus precatorius (69
Variable
105-40
105-70
105*00
0-28
0-66
0-7
seeds ; Leguminosse)
Canavalia obtusifolia (8
Variable
102-40
102-50
102-55
0-15
0*2
seeds ; Leguminosas)
Guilandina bonducella
Imperme-
306-60
306*60
306*60
0*00
o'oo
o'oo
(7 seeds ; Legu-
able
minosse)
Entada scandens (3
Imperme-
809*60
8o9 - 65
809-45
O'OO
0'02
o'oo
seeds ; Leguminosse)
able
Adenanthera pavonina
Imperme-
104-80
104*80
104-85
0*05
o'oo
(22 seeds ; Legu-
able
minosse)
The seeds had been five months in England when weighed in October 1907 ; two
months in Jamaica in January 1908, when weighed in that island ; and one month in
England when weighed in April 1908. All the seeds retained their germinative
powers after the experiment, with the exception of those of Achras and Chrysophyllum,
which were sound, but did not germinate.
It may be concluded from the data in this table that the
following were the results of the transportation of these seeds
from the temperate zone to the tropics and back. The range
of the variation in weight of the permeable seeds was 3 to 4
per cent., and that of the variable seeds considerably under i
per cent. ; whilst the range of the impermeable seeds may be
regarded as " nil," or, if present, as probably instrumental and
therefore negligible. In the case of both the variable kinds
i6o
STUDIES IN SEEDS AND FRUITS
The first
method of
determining
the hygro-
scopic range.
Experiment
in Jamaica.
of seeds the proportion of permeable seeds was probably very
small, that is to say, under 10 per cent.; and doubtless the
change of weight was experienced by a very few seeds. The
rise in weight of the three permeable kinds of seeds in Jamaica
and the fall after returning to England are characteristic ; but
the difference between them is probably due to the varying
hygrometric conditions of the air when the two sets of obser-
vations in England were made. On the whole, however, it may
be considered that the changes in weight experienced by these
permeable seeds between warm and cool latitudes are within
the limits of the hygroscopic range defined a few pages back.
In all experiments for determining the limits of hygroscopic
variation it is requisite that the seeds should have completed
the drying process and that they should be, as far as their
water-contents are concerned, in a state of equilibrium with
the air. The method at first employed in investigating the
hygroscopic behaviour of seeds was, as already indicated, to
weigh them daily for ten or fourteen days when the weather was
changeable. The variation was then stated as a percentage of
the total weight of the seed, and this was termed the " hygro-
scopic range." In such experiments four or five kinds of seeds,
of both the permeable and impermeable types, were experi-
mented on at the same time. The results of one of these
experiments in Jamaica are given below in the form of a
diagram ; and in order to obtain a more graphic effect, they
have all been computed for 1000 grains of each kind of seed,
whilst the prevailing weather conditions as regards rain have
been roughly indicated by black and white squares. The
following seeds were employed :
112 seeds of Anona palustris, weighing 440-8 grains.
74 Anona muricata (Sour Sop), 47'$ j>
85 Citrus decumana (Shaddock), 334'7 ?>
212 Adenanthera pavonina 1000-0
3 Entada scandens 1087-3
The first three are permeable seeds, the ranges for the two
species of Anona being 1-3 and i"i per cent., whilst that for
HYGROSCOPICITY
161
the Shaddock was 1*6 per cent. But these do not represent
the maximum hygroscopic ranges. The Shaddock seeds in
another experiment in England gave a range of 2 per cent. ;
and probably the swing of the range, including ordinary extremes,
would amount to nearly 3 per cent, for all the permeable seeds
here experimented on. The last two are typically impermeable,
and the small variation exhibited is probably instrumental.
DIAGRAM CONTRASTING THE BEHAVIOUR OF PERMEABLE AND IMPERME-
ABLE SEEDS AS RESPECTS THEIR VARIATION IN WEIGHT DURING
TEN DAYS OF CHANGEABLE WEATHER IN JAMAICA, THE RAIN
BEING INDICATED BY BLACK.
(For further explanation see the preceding remarks. The three first-named are per-
meable and the last two are impermeable.)
Anona palustrii
Anona muricata .
Citrui decumana .
Entada scandens .
Adenanthera pavontna .
997-3-1010-4= 13-1
997-4- 1009-3= I r-g
looo-o 1016-1 = 1 6- 1
i ooo-o i ooo- 1 = o- 1
lOOO'O IOOO-I= O-2
In course of time, however, I discovered that although
the method described and illustrated in the previous pages The method
exhibited the ordinary hygroscopic response of the permeable adopted of
seed to the usual weather changes within a limited period, J^^"""^
it did not give me the whole range of the variation, such as scopic range.
ii
1 62 STUDIES IN SEEDS AND FRUITS
one would look for if the experiment was continued for a
year. A chance observation led me to believe that the whole
range was quite twice as much as that indicated in the fore-
going experiments ; and I soon found, on transferring the
seeds from a cool, damp room without artificial heat to a dry
cupboard, where the temperature (owing to the vicinity of
hot-water pipes) was from 10 to 15 F. warmer, that the
range of the hygroscopicity was much increased. In such
circumstances the seeds of Anona, Shaddock, Canavalia ensiformis,
etc., which, as first tested, exhibited a variation in weight of
i to i^ per cent., now showed an increased range of 2 or 3
per cent. Accordingly, 1 subjected the seeds to this new
proof, and the results are those given in the following pages.
The seeds were transferred from the cool room to the warm
cupboard for two days and back again to the room, the mean
of the two results being taken. Typical impermeable seeds
used as checks in many experiments displayed no change in
weight, except of a trifling nature.
RESULTS OF THE AUTHOR'S OBSERVATIONS ON THE
HYGROSCOPICITY OF SEEDS.
I. IMPERMEABLE SEEDS. (Hygroscopicity " nil.")
A typical impermeable seed exhibits no change in weight,
except such as can be attributed to instrumental error, or to
a little loose tissue adhering to the scar or to the raphe. For
example, a seed of Guilandina bonducella 40 grains in weight,
and a seed of Entada scandens weighing 400 grains, would
show the same variation during a month of cr i grain, which
is so small that it may be safely attributed to other causes
than to normal hygroscopicity.
The seeds actually tested by me include the following :
Adenanthera pavonina, Dioclea reflexa, Entada scandens, Guilandina
bonducella, Leuc<ena glauca, Mucuna urens, etc. But of course
all the seeds mentioned in the Impermeable Group in
Chapter V would, when typical, display no hygroscopic re-
H YGROSCOP1CITY 1 63
action, excluding seeds like those of Ipomosa pes-capr<e, where
the covering of hairs would give hygroscopicity, though the
seed bared of hairs is non- hygroscopic. The influence of
hairs is dealt with a few pages further on.
Since impermeable seeds are not infrequent in nature, as
is shown in Chapter III, it follows that a large number of
seeds fail to make any response to the weather changes, and
are therefore non-hygroscopic. Here would belong the seeds
of many of the Australian Acacias and a number of the 180
"macrobiotic" or long-lived seeds included in Professor Ewart's
list (Proceedings^ Royal Society of Victoria^ 1908), though a large
proportion also would belong to the Variable Group, where
plants possess both permeable and impermeable seeds.
As illustrating the behaviour of impermeable seeds in
the balance, there are appended the actual results obtained in
the case of those of four species during periods of from ten
to sixty days. It will be noticed, as before remarked, that
the same slight variation of from 0*1 to 0*2 grain is displayed
by large and small samples, being evidently in great part
instrumental. We are here only concerned with the absence
of the ordinary hygroscopic reaction in the course of a few
weeks. The extent to which this behaviour is persistent will
be discussed in Chapter X.
[TABLE
164
STUDIES IN SEEDS AND FRUITS
SOME RESULTS ILLUSTRATING THE ABSENCE OF A TRUE HYGROSCOPIC
REACTION IN IMPERMEABLE SEEDS, THE SLIGHT VARIATION BEING
INSTRUMENTAL. (Daily observations made in the short experiments
only.)
Number
Length of
Variation of weight
Locality of
of seeds.
experiment.
in grains.
experiment.
Guilandina bonducella .
3
1 8 days
990*43 990*60 or 0*17
England.
i
60
3S'3~ 35'iooro'o7
England.
Quartz pebble
60
38*40- 38*47 or 0*07
England.
Dioclea reflexa
ii
10 ,,
1042*00 - 1042*2 or o'2o
Grenada.
Entada scandens .
3
i ,,
1087*4 - IO $7'S or o'ro
Jamaica.
Leucsena glauca .
332
10
250*0 - 249*9 or ' 10
Grenada.
II. PERMEABLE SEEDS. (Hygroscopicity 2 to 5 per cent.)
(The hygroscopic range of a seed is the amount of variation stated as a percentage
of the average weight. Thus, if a seed varied between 98 and 102 grains, the range
would be 4 per cent. The methods of obtaining these results are described a page or
two back.)
Hygroscopic
range.
Average weight of
a seed in grains.
^Esculus Hippocastanum (Horse-chestnut) .
4*5 per cent.
130*0 grains.
Allium ursinum
4*0
0*12
Anona muricata (Sour Sop)
2*8
6*0
,, palustris
2*6
4*0
,, reticulata (Custard Apple) .
2*8
4*0
,, squamosa (Sweet Sop) ....
3'3
5'
Bignonia (species of)
3'S
S'
Canavalia ensiformis
2 "5
24*0
Chrysophyllum Cainito (Star Apple)
1*8
12*0
Citrus decumana (Shaddock) ....
2*4
4 '5
Datura Stramonium
3'
0*13
Dolichos Lablab
1*1
4*0
4*0
? 1 *O
Hura crepitans (Sandbox Tree) ....
T w
2*2
33 "
2O*O
Iris foetidissima .......
4*0
0*8
Luffa acutangula (Loofah)
2*2
I *0
Phaseolus multiflorus (Scarlet-runner) .
S'
1 8*0
Pisum sativum (Peas) wrinkled ....
6*0
6 '5
,, ,, smooth ....
4'5
5'
Primula veris (Primrose)
4' 1
0*012
Ravenala madagascariensis (Travellers' Palm)
2*0
5'
Ricinus communis (Castor Oil) ....
'5
3'S
Sapota Achras (Sapodilla)
"'9
10*0
Scilla nutans (Bluebell)
4*0
0*1
Swietenia Mahogani (Mahogany) ....
2*0
37
Tamus communis
4*0
0*25
HYGROSCOPICITY
.65
III. VARIABLE SEEDS. (Hygroscopicity variable.)
(Variable seeds are those where some are permeable and others impermeable, the pro-
portions being very inconstant, so that the hygroscopic range for different seed-samples
would vary much, and could only be characterised as intermediate between that for im-
permeable seeds (nil) and that for permeable seeds (2 to 4 per cent.).
Hygroscopic
range
(variable in
different
samples).
Average weight of
a seed in grains.
0-5 per
* '5
2'0
7
'S
3'o
0-6
2'0
'3
'3
0-6
0-7
2'O
0'2
0-6
'5
I'O
'5
I'O
I '0
n
cent.
t
1-5 gra
2'0
2 '3
0-33
4'0
IO'O
IO'O
4-5
I2'0
*7
4'0
IO'O
6'6
S'o
17-0
3 '2
1 3'
25-0
IO'O
20 "o
3-0
ins.
Albizzia Lebbek
Aquilegia (species of) .
Caesalpinia Sappan (A), mostly permeable .
,, (B), mostly impermeable
Caesalpinia sepiaria
Canavalia obtusifolia .
Canna indica
Cassia fistula
,, marginata .
Entada polystachya (A), mostly permeable .
,, (B) ,, impermeable
Erythrina corallodendron
,, indica .
Ipomcea tuberosa .
Poinciana regia .
Tamarindus indicus
Thespesia populnea
From the results of the observations on the hygroscopicity of
a number of seeds which are given above it may be inferred
(1) That permeable seeds under ordinary weather conditions General
vary to the extent of 2 or 3 per cent, of their weight drawn S from
in the course of two weeks, though the range may *^ e auth r 's
be reduced to I per cent, in equable conditions, and
increased to 4 or 5 per cent, when the weather is
characterised by extreme changes ;
(2) That impermeable seeds have practically no hygroscopic
reaction, such small changes as do occur, as of I in
1000 or of i in 10,000 of the weight, being either
instrumental or connected with loose tissue adhering
to the scar or to the raphe ;
1 66 STUDIES IN SEEDS AND FRUITS
(3) That with variable seeds, where there is a mixture of
permeable and impermeable seeds, the range is inter-
mediate in amount, frequently about i per cent., but
varying of course with the proportion of permeable
seeds.
With those " variable " seeds, as with Entada polystachya
and Ctesalptnia Sappan, where it is possible to distinguish by
inspection between the two types of seeds, the difference in
the hygroscopic reaction is well marked. Thus, with the
first-named plant, a sample of permeable seeds displayed a
range of 2 per cent., whilst a sample of seeds almost all
impermeable gave a range of 0*2 per cent. So also with
Ctesalpinia Sappan, I found that seeds which had fallen to
the ground in the ordinary way were mostly impermeable
and had a range of cr6 per cent. ; whilst those remaining in
the dried but closed pod on the tree were nearly all permeable
Thehygro- and varied 3 per cent, in their weight. It would be quite
action as" a possible for the gardener or the agriculturist to devise a
V ~ rou g n an< ^ re ady rule by which the proportions of hygro-
scopic permeable seeds and of non- hygroscopic impermeable
seeds in any sample could be approximately estimated. Thus,
assuming that with seeds of a certain kind the complete
hygroscopic reaction when all the seeds were permeable was
3 per cent., then a sample of the same seeds that gave a
range of 1*5 per cent, might be regarded as probably contain-
ing only 50 per cent, of permeable seeds. At all events a
marked departure from the normal might give a valuable hint
to the gardener in making a selection.
The influence The influence of the coats in restraining the hygroscopic
nf i"Vi* dppH
coats on the variations of permeable seeds has already been briefly alluded
scopitity of to i n Chapter IV. It was there shown that the hygroscopic
permeable range of the seed of Canavalia ensiformis with its coats intact
(2'5 per cent.) was less than in the case of the seed where the
coats had been punctured (3^0 per cent.), and that this again
was less than with seeds bared of their coverings (4*0 to 4*5
per cent.), thus clearly indicating a progressive increase in the
HYGROSCOPICITY
167
hygroscopic variation of the seed in proportion to the degree
of loss of the protection it owes to its coats. The same
indications are presented below in the tabulated results for
five kinds of seeds belonging to the four very different families.
It will, however, be noticed that there is a very considerable
difference between seeds in respect to the restraining influence
of the seed-coverings on the hygroscopic reaction. In watery
seeds like those of the Horse-chestnut, Broad Bean, and
Canava/ia ensiformis, it is evidently considerable, whilst with oily
seeds like those of Anona reticulata it may be so small as to be
almost negligible. In such experiments it is requisite that
the seed should have completed its drying process, or at all
events that it should be drying very slowly.
With reference to the differentiation between the coats
and the kernel in this respect, such a contrast would not
indicate a factor of much importance in determining the
nature of the range, since, although the inner layer of the
coats, being often looser in texture than the outer skin, might
be expected to be more hygroscopic, it would not be exposed
directly to the air, as in the case of the detached seed-coverings
in an experiment. However, the results tabulated below show
that the seed in its coverings is less hygroscopic than either
the coats alone or the bared kernel.
COMPARISON OF THE HYGROSCOPIC RANGE OF PERMEABLE SEEDS
WITH AND WITHOUT THEIR COATS.
(The range is the variation stated as a percentage of the average weight. The seed
and its parts were in each case tested together.)
Seed in
Bared
Coats
Age of
its coats.
kernel.
alone.
seeds.
^Esculus Hippocastanum (Horse-chestnut) .
Anona reticulata (Custard Apple)
I 'O
2'8
1-9
3-0
3' 1
6 months.
1 8 months.
Canavalia ensiformis ....
A 1-5
B 2-5
3 '3
4-0
4'i
9 months.
6 months.
Citrus decumana (Shaddock)
2-4
3' 1
3 '4
4 weeks.
Faba vulgaris (Broad Bean)
2'0
3 '2
2'6
8 months.
Note. These results do not represent the full range in the case of the Horse-chestnut,
the experiment being a short one.
i68
STUDIES IN SEEDS AND FRUITS
The effect of A few remarks may be made on the influence of age on
sf e e d P s n h y gro . the hygroscopicity of seeds. If it is a purely physical process
scopicity. an( ^ independent of life, we would not expect any marked
effect to be shown with age, provided that the seeds, when
first experimented on, had completed the drying process. But
if the seed is still slowly drying, we should look for a slight
increase in the " hygroscopic range " as time goes on, a result
that would be due to the seed losing weight, whilst the
hygroscopic variation remained unchanged. In such experi-
ments it is absolutely necessary that the seeds of different
ages should be subjected at the same time to the same test.
Without this condition the results would not be worth com-
paring, and for this reason many of my data are excluded.
However, it will be seen from my experiments on the
seeds of the Horse-chestnut (sEsculus Hippocastanum} and of
Tamus communiS) which fulfilled this condition, that the effect
of age is slight.
RESULTS ILLUSTRATING THE EFFECTS OF AGE ON THE HYGROSCOPIC
RANGE OF SEEDS, THIS RANGE BEING THE VARIATION IN WEIGHT
STATED AS A PERCENTAGE OF THE AVERAGE WEIGHT OF THE
SEEDS.
2 months.
7 months.
13 months.
19 months.
31 months.
^Esculus Hippocastanum
(Horse-chestnut)
Tamus communis
4'3
i '95
4*00
2-08
2 "40
The samples of the Horse-chestnut consisted of 4 to 7 seeds, weighing in all from
500 to 1000 grains. Those of Tamus communis included about 150 seeds, weighing
about 37 grains.
The effect of At first sight it might appear probable that a seed's hygro-
halrs oTa" sco picity would be markedly increased by a hairy covering ;
seed'shygro- but a little reflection will show that this cannot usually be
scopicity. (
expected. It we take an impermeable seed 100 grains in weight,
of which 10 grains belong to the covering of hairs, a propor-
tion, I should imagine, much above the average, and if we
assume that the hairs have a hygroscopic variation or range of
HYGROSCOPIC1TY 1 69
10 per cent., which again is much more above than below the
average for vegetable materials, then the variation for the
entire seed would be only i per cent., since, as an impermeable
hairless seed, it would be non-hygroscopic. Or let us take a
permeable seed corresponding to the above in all its characters,
except that when deprived of its hairs it shows a hygroscopic
reaction of 5 per cent. It is obvious that this reaction would
be but slightly increased by the hairy covering, since the in-
creased hygroscopicity of the hairs would be concerned only
with one-tenth of the seed's weight.
But in thus depreciating in advance the effect of hairs on
a seed's hygroscopicity we have assumed that the covering of
hairs displays a more pronounced hygroscopic reaction than
is exhibited by an ordinary hygroscopic hairless seed. My
observations and experiments, however, go to show that this
is not the case. We will take the impermeable seeds of
Ipomaea pes-capr^e, which have a dense pubescent covering and
an average weight of 1\ to 3 grains. As shown in Chapter IX,
the weight of the hairs barely amounts to 3 per cent, of the
total weight of the seed. To test the influence of the hairs on
the hygroscopicity of the seed two samples, containing each
about twenty-five seeds, were experimented on, one with the
hairs scraped off and the other with the hairs remaining. The
first gave a hygroscopic reaction of 0*7 per cent., and the second
of i'o per cent. The hairs, in fact, made little or no difference,
and the slight change that occurred was probably connected
with quite a different cause, namely, the occurrence of one
or two permeable seeds in each sample, an event which my
flotation experiments indicate as not uncommon.
Still more unexpected were the results of my experiments
on the hairy seeds of a species of Gossypium, probably G.
hirsutum, which are described in the same chapter. The
average weight of the entire seed is about 1*5 grain, and of
this nearly one-half, or 44 per cent., is made up by the hairs.
A sample of scraped seeds and a sample of hairy seeds
displayed a similar but slight hygroscopic reaction of rather
-I yo STUDIES IN SEEDS AND FRUITS
under i per cent. Ordinary cotton-wool, it may be added,
exhibited under my tests a hygroscopic variation of only 2 per
cent., which is merely what one would look for in hairless
permeable seeds.
Hygro- We may infer from Berthelot's principle that hygroscopicity,
germination, being associated with the water which the seed, living or dead,
holds in maintaining its equilibrium with the air, has nothing
to do with germination. It has, however, often the appearance
of bringing about germination. One may gather fresh acorns,
separating at a touch from the cupule on the tree, and leave
them exposed in a saucer in an ordinary room for two or
three weeks, and some of them will germinate. One may
stand a dry, open test tube half filled with seeds of Abrus
precatorius in water in a tall glass vessel which is subsequently
covered over, and in the course of a week or two a few of
them will be found in a germinating or at least in a swollen
condition. But in neither case has this anything to do with
the water of hygroscopicity.
In the case of the acorns, as shown in a later chapter, they
still contain, on falling out of the cupule, a large excess of
water, and it is this excess that is utilised in the early
germination. In this freshly detached state the embryo of the
future oak as it lies enclosed in the shell is almost in the act
of germination, and indeed is apt to germinate in spite of its
drying condition. As they lie drying on the table the chances
are fairly balanced whether the acorns will germinate before
the loss of water renders that impossible, or whether the
process of drying will proceed so fast that the germinative
capacity is unable to assert itself.
In the case of Abrus precatorius y should the vessel be
exposed to the usual diurnal changes of temperature, con-
densation of the water-vapour in the heavily charged air would
probably occur and liquid water would be likely to come
in contact with the seeds, thus introducing another order
of phenomena. Nobbe (pp. 105-108) lays stress on the
point that contact with liquid water is essential for inducing
HYGROSCOPICITY 1 7 1
the swelling that precedes germination, and that the increase Thehygro-
in the water-contents due to hygroscopicity is quite insufficient Ictwn does
for the purpose. The question whether, under ordinary
conditions, seeds will take up sufficient water from the air for
germination he answers in the negative ; but he considers that
germination would be likely to occur when through frequent
great changes of temperature, condensation takes place on the
surface of the seed. In the extreme conditions reproduced in
his experiments, when seeds of Flax and of the Kohl-rabi were
exposed for many days to air saturated with moisture, he found
that an increase in weight of 22 or 23 per cent, did not lead to
germination. In such experiments germination would occur
only when, through condensation within the vessel, liquid water
comes into contact with the seeds.
Jodin put the distinction between the increase of water due
to hygroscopicity and the amount of water required for ger-
mination very clearly in the case of peas. He shows that
whilst the minimum amount of water required to be absorbed
for germination amounts to 67 per cent, of the weight of the
resting seed, the greatest increase in weight involved in the
hygroscopic range of peas is not more than 23 per cent., a
quantity he characterises as insufficient to provoke germination. The ger-
Although he found that the water of hygroscopicity was quite ^o'SitUes
insufficient to produce germination, the results of one of his * bove the .
o ' hygroscopic
experiments described in Note 4 of the Appendix might have maximum
been interpreted in this sense by a superficial observer. In thesatura-
order to ascertain the minimum amount of water requisite for tlonlmut -
germination, he placed the peas on a platinum support suspended
in moist air, the metal condensing the aqueous vapour in fine
drops and communicating the liquid water to the peas. It is
evident from Jodin's experiments that, as far as the water-
contents of the seed are concerned, the germination point lies
between the maximum of the hygroscopic range and the limit
of the seed's capacity for absorbing liquid water, or, in other
words, between the hygrometric extreme and the saturation
point.
IJ2
STUDIES IN SEEDS AND FRUITS
The maxi-
mum ofthe
hygroscopic
capacity.
Nobbe's
experiments.
And now we have to inquire into the nature of this extreme
limit of a seed's hygroscopicity. This is a difficult matter and
one concerning which awkward questions are likely to be raised.
In my own experiments the object was to ascertain the hygro-
scopic range of seeds during a fortnight of changeable weather ;
and the results procured, as shown in the table, differ but little,
whether obtained in the tropical climate of Jamaica or in the
temperate climate of England. Permeable seeds, according to
my observations, vary usually 3 or 4 per cent, of their weight.
Jodin found that in the course of a year's exposure to ordinary
air-conditions the water-contents of peas varied according to
the temperature and hygrometric condition of the atmosphere
from i o to 30 per cent, of the seed's dry weight, or, as he puts
it, between o'i and 0^3 gramme for each gramme of water-free
material. Stated in terms of the wet weight, that is, of the
seed with its water-contents, this represents a variation of from
9 to 23 per cent., and an annual range of 13 or 14 per cent.
This hygroscopic range for peas during a year is considerably
larger than the range assigned to them in my own observations,
namely, 4 to 6 per cent. The difference is probably due as
much to the methods employed as it is to the differences in
the length of the experiments. Such a range was never
indicated in the case of the seeds of Canavalia ensiformis, the
total variation of which in a two years' experiment amounted
to less than 6 per cent, of their weight ; nor was it evidenced
in the course of my " long-period " weighing experiments, the
results of which are discussed in Chapter X.
Serious obstacles are apt to arise in testing the maximum
capacity of a seed for absorbing water-vapour from the air.
They were encountered by Nobbe in his experiments on flax-
seeds (pp. 105-108). Such seeds, after being exposed for nine
days to air saturated with moisture, increased their weight by
1 6^ per cent., whilst others kept for the same period in ordinary
air added from ^ to i^ per cent, to their weight. In another
experiment on these seeds in saturated air, which covered
twenty-six days, it was found that under warm conditions
HYGROSCOP1CITY 1 73
(mean temperature 18 C, or 64 to 65 F.) there was an
increase in weight of 22-5 per cent., and under cool conditions
(mean temperature about 5 C., or 41 F.) an increase only of
4- 1 per cent., whilst with seeds exposed in turn to both the
warm and cool conditions there was an increase of 16*6 per cent.
One is inclined to think that condensation occurred in the
experiment under warm conditions. The seeds were placed
in a porcelain vessel standing in water and covered with a
glass globe, the range of temperature being 13 to 21 C., or
55 to 70 F. With a range of about 15 F., condensa-
tion is quite possible ; and if it occurred at night it might
not be evident in the daytime. We are told that the occur-
rence of mildew brought the experiment to a close, and that
the seeds were still adding to their weight at the end. The
same method was adopted with all the flax-seed experiments,
and also with the seeds of the Kohl-rabi (Brassica oleracea
caulorapa) y which increased their weight 23-5 per cent. It is
to be noted that this investigator was not inclined to accept
Hoffmann's much smaller estimates for the hygroscopic increase
of weight of the seeds of Linum and Brassica^ namely, 4-7 and
4'6 per cent, respectively.
The trend of my own results is all in the direction of
Hoffmann's smaller determinations of a seed's hygroscopicity.
I should imagine that flax-seeds (Linum), containing as they
do so much colloid material capable of combining with water The danger
in the form of mucilage, would give results far from typical. suchexperi-
But of more importance still is the fact that mould or mildew ments -
interfered with both the experiments on flax-seeds made by
Nobbe, where the gain in weight reached i6|- and 22^- per
cent. ; and in neither case had the increase ceased when the
experiment ended. The danger in all experiments where
seeds are exposed to air saturated with moisture is the develop-
ment of mould, which, on account of its hygroscopic properties,
would go far to vitiate the results. Its onset is insidious ;
and, as was often indicated in my drying and similar experi-
ments in the tropics, long before the fungus became evident
The hygro-
scopic be-
haviour of
pods.
STUDIES IN SEEDS AND FRUITS
to the eye there was a marked increase of weight and a slight
softening of the affected materials.
But I may remark that the more moderate view of the
range of hygroscopic variation for seeds is supported by the
results of my observations on air-dried fruits. Some of them
relating to pods or legumes are tabulated below.
A. RESULTS OF EXPERIMENTS ON THE HYGROSCOPIC RANGE OF ENTIRE
AIR-DRIED LEGUMES OR PODS, INDEHISCENT AND CONTAINING THEIR
SEEDS. (The hygroscopic range is the variation in weight stated as a
percentage of the total weight.)
Number and
weight of pods
in grains.
Length
of experi-
ment.
Locality of
experiment.
Hygro-
scopic
range.
Weather.
Albizzia Lebbek
One pod 25 grains
ii days
West Indies
4'3%
Wet and
dry.
Cassia fistula .
i, 7' ,,
2 months
England
3*4,,
Great
contrasts.
>
,. i,S*S .
*
3'4,,
Great
contrasts.
Poinciana regia
i>532 ,.
2
it
*7 ,,
Great
contrasts.
Entada polystachya
> 164 ,,
2
ii
3-8,,
Great
contrasts.
>i >t
The same pod
7 days
West Indies
4 '2
Wet and
dry.
Pisum sativum (Pea)
Two pods, total 120
See note
England
47
See note.
grains
Note. In all the experiments except that on Pea- pods, the pods were kept in one
room. The experiments, occupying two months, lasted from June to August. The data
for the Pea-pods were obtained by transferring them from a cool and moist room
(temperature 50 to 55 F.) to a warm and dry cupboard (temperature 65 to 70 F.) and
weighing them after four days.
B. COMPARISON OF THE HYGROSCOPIC RANGES OF THE AIR-DRIED SEEDS
AND FRUIT-CASE OF PISUM SATIVUM (Poo) AND OF IRIS FCETIDISSIMA
(CAPSULE) UNDER THE SAME CONDITIONS.
Iris foetidissima
Pisum sativum .
H. R. of seeds 4*0 per cent.
,, 4*5 ..
H. R. of fruit-case 3 '6 per cent.
,, 47 ,.
It will be seen from these tables that the variation in weight
in response to the changes in atmospheric humidity was usually
HYGROSCOPICITY 175
3 or 4 and never over 5 per cent., whatever the nature or size
of the pod. These pods, all of them dry, intact, and contain-
ing their seeds, range in length from 3 or 4 inches, as in the
case of the Pea, to a couple of feet, as with the pods of the
species of Cassia and Poinciana ; and there is a great contrast
between the relatively fragile appearance of the first-named
and the tough, woody aspect of the two last. However, not-
withstanding the great differences in size, weight, and texture
of these pods, their changes in weight due to the hygroscopic
reaction are not far apart. The long pods of Cassia fistula are
very sensitive to the hygrometric condition, and vary in weight
whilst being handled for the balance. One of them lost
i per cent, of its weight whilst a wet morning was giving
place to a fine evening. This amounts to a great deal in the
balance, since the pods when dry range between 1500 and
2000 grains in weight. They are durable, easily weighed,
and might prove useful as hygrometers.
It would seem from the foregoing data that permeable
leguminous seeds possess much the same degree of hygro-
scopicity as their pods. Thus under the same conditions peas
gave a range of 4-5 per cent., and the pods with seeds removed
4*7 per cent. (The same principle is also indicated in the case Pods are
of Iris fastidissima, where the ranges for the seeds and the capsular
valves were 4*0 and r6 per cent.) However, there is no seeds are
. . permeable or
such relation between the impermeable seed and its pod. All impermeable.
the impermeable seeds with which I am acquainted, such as
those of Guilandina bonducella, Mucuna urens, Diodea reflexa,
Entada scandens, etc., are enclosed in pods that in the dry state
readily take up and absorb moisture ; whilst in the case of
the hygroscopic pods of the species of Cassia, Poinciana, Entada,
and Albizzia, dealt with in the table, many of the seeds are
impermeable, and the hygroscopic range for any sample of
seeds chosen at random is consequently low, usually not over
i or 2 per cent., but varying according to the proportion of
permeable seeds. As illustrating the hygroscopic behaviour
of pods emptied of their impermeable seeds, I may mention
la
176 STUDIES IN SEEDS AND FRUITS
that the dry open pods of Gullandma bonducella and C<esalpinia
Sappan, as they lay on the table in my room in Grenada, used
to vary in their weight as much as i or 2 per cent, from day
to day, especially between the evening and the following
morning.
In concluding this chapter we may observe that the question
we put to ourselves a few pages ago as to the extreme limit of
a seed's hygroscopicity is very far from being answered, and
perhaps it may prove to be not altogether pertinent to the
subject we are discussing. With the data at our disposal it
seems unnecessary to follow up this special point any further
at present ; and indeed it will appear from the subsequent
chapters that a number of queries claim a reply first.
SUMMARY
(1) Hygroscopicity in a seed is defined as the variation of its water-
contents in response to the changes in the hygrometric state of the
atmosphere (p. 147).
(2) After referring to the important memoir on the subject of
hygroscopicity in general by Leo Errera and to the display of this
quality by vegetable materials in particular, special attention is directed
to the researches of Jodin and Berthelot. Whilst the first-named
investigator approached the subject from the biological and the second
from the physical side, both arrived at the same conclusion : that we
are here concerned with a quality that is independent of vitality
(p. 148).
(3) Jodin, experimenting on living and dead peas, found that they
exhibited much the same hygroscopic variation in the course of a year's
exposure to ordinary air-conditions (p. 148).
(4) Berthelot, experimenting on different vegetable materials (leaves
and stems of grasses, etc.), shows that the peculiar property possessed by
air-dried vegetable substances and some other materials of regaining
from the air the water which they yield up when exposed to a
temperature of 100 to 1 10 C. is a function of the hygrometric state of
the atmosphere and is essentially a physico-chemical process independent
of life. We will take as illustrating this principle 100 grammes of
fresh plant-substance which is reduced to 50 grammes by air-drying in
an ordinary room. Exposing it then to a temperature of 1 00 to 1 1 o C.,
its weight is further reduced to 40 grammes ; but on being allowed to
HYGROSCOPICITY 177
remain in the room for a few days, it replaces the water lost in the oven
by abstracting it from the air and returns to its original air-dried weight
of 50 grammes, subject only to the ordinary hygroscopic variation.
Precisely the same air-dried weight is ultimately reached if the fresh
material is put at once in the oven. In the same way, the leaf that
dries and dies naturally on the plant, if placed in the air after the heat
test, regains the water lost in the oven. This is Berthelot's principle
of reversibility (p. 149).
(5) The author, after confirming this principle by appealing to his
experiments on Hazel leaves, shows that it presents us with the simplest
mode of differentiating the water-contents of plant-tissues, namely,
into (a) the water of hygroscopicity, which they hold whether living or
dead, and (b] the water of vitality, which they lose when they die
(p. 151).
(6) He points out that the chemist, when producing by synthesis
organic vegetable substances, would allow the atmosphere to supply the
water of hygroscopicity, whilst he himself in his creative role would
have to furnish the water of vitality. To emphasise this point he
gives the result of an experiment on bread, and shows that just as
moist fresh plants after being exposed to a temperature of 100 C. can
only recover from the air the water lost by air-dried plants in the oven,
so bread after the same heat test only gains back what was originally
in the miller's flour, but cannot recover the water the baker put into it
(P- r 53)-
(7) After giving a further illustration of the principle of Berthelot
in the results of an experiment on the seeds of Phaseolus multiflorus^ the
author proceeds to deal with the implications of this principle (p. 154)-
(8) The first is that air-dried resting seeds, both permeable and
impermeable, contain only the water of hygroscopicity ; and the
second, which follows from it, is that there is in such seeds no water
associated with any vital function (p. 155).
(9) Since some seeds can retain their germinative powers after
being desiccated to an extreme degree, the presumption arises that
in their resting state they can dispense with water altogether ; and
it is urged that we are not called upon to assign a function to the
minute amount of water that may remain after extreme desiccation.
A perfectly dry seed protected from the air alone possesses the
potentialities of immortality (p. 156).
(10) Instead of favouring the longevity of a seed, water is
regarded here as the source of its greatest danger. Appeal is then
made to the biological significance of hygroscopicity in seeds, and
it is shown that whilst the constant hygroscopic reaction limits the
life of permeable seeds, its absence in impermeable seeds ensures
their longevity. The seed that has the best chance of living for
12
1 78 STUDIES IN SEEDS AND FRUITS
ever is one where a perfectly dry embryo is locked up in a hard
impermeable shell or covering (p. 157).
(n) Coming to the details of his own observations on hygro-
scopicity, the author, after observing that in the nature of things
considerations of hygroscopicity are concerned only with permeable
seeds, proceeds to discuss the effects of change of climate on the weight
of seeds. In this connection he shows that, as a result of transporta-
tion from the temperate zone to the tropics and back, permeable
seeds varied from 3 to 4 per cent, of their weight, variable seeds
(both types in the same plant) less than i per cent., and impermeable
seeds practically not at all. The changes of weight, he points out,
are included within the ordinary hygroscopic range (p. 158).
(12) The methods of determining the range of hygroscopicity
in seeds in terms of the variation of their weight are then described,
and after giving the results of his observations on more than sixty
kinds of seeds, of all sizes and characters, he forms the following
general conclusions :
(a) That permeable seeds vary usually to the extent of from 2
to 3 per cent, of their weight, though the range may
be as little as I per cent, in equable atmospheric conditions,
and as great as 4 or 5 per cent, when the changes in the
relative humidity of the air are extreme ;
(b) That impermeable seeds have practically no hygroscopic
reaction, their weight remaining unchanged in spite of
great variations in the hygrometric state of the air ;
(c) That with variable seeds, where there is a mixture of permeable
and impermeable seeds, the range for any ordinary sample
is usually about i per cent., differing according to the
proportion of permeable seeds (p. 165).
(13) Special stress is laid on the value of the hygroscopic reaction
stated in terms of weight as a test for proving seeds (p. 166).
(14) Additional data are given, as supplementing those already
given in Chapter IV, on the influence of the coats on the hygro-
scopicity of permeable seeds, and supporting the previous conclusion
that the coats tend to restrain the hygroscopic range (p. 167).
(15) Results of observations are then given on the effects of age
on the hygroscopic behaviour of seeds, and they are shown to be
slight (p. 1 68).
(16) Contrary to one's expectation, it is found that a hairy covering,
whilst it gives a small hygroscopic range of less than i per cent,
to impermeable seeds, but slightly if at all increases the hygroscopicity
of permeable seeds (p. 169).
(17) Since it follows from the principle of Berthelot that the water
of hygroscopicity could have little to do with germination, appeal
HYGROSCOPIC1TY 1 79
is made to the results of experiments made by Nobbe, Jodin, and the
author in this connection ; and it is established that the normal
hygroscopic reaction cannot provoke germination, the minimum
amount of water required for germination being far in excess of that
which a seed would take up unaided from the air (p. 171).
(18) The nature of the extreme limit of a seed's hygroscopicity
is then discussed ; and the author, after laying stress on the especial
risks of mould and condensation to which such experiments are
liable, follows the indications of his own experiments in accepting
a range in weight of 5 or 6 per cent, of the average weight of the
seed as the greatest amplitude of normal hygroscopic variation, the
usual range, however, being only 2 or 3 per cent. Hoffmann's
results point in the same direction, and precisely the same limits
to the hygroscopic range of weight are established by the author's
observations on the weight of dry pods (p. 172).
(19) The results of these observations on air-dried legumes are
then tabulated, and it is shown that leguminous pods with permeable
seeds display much the same degree of hygroscopicity as their seeds,
the pod being hygroscopic whether the seeds are permeable or
impermeable (p. 174).
(20) Although the ordinary maximum of the normal hygroscopic
range has been above stated, the author regards the possible extremes
of a seed's hygroscopicity as outside the present inquiry.
CHAPTER VIII
A LAST WORD ON THE HYGROSCOPICITY OF SEEDS
THE seed's capacity of regaining from the air the water driven
off by exposure to a temperature of 100 C. has been discussed
pretty much in the order in which the investigation has been
pursued. We have plodded on without always knowing where
the road was leading to, diverging first to one side and then to
the other, feeling our way often in the darkness, until at length
we have stumbled on a clue that throws much light on the
whole inquiry. The principle of Berthelot only came under
our notice when the investigation was far advanced, and of
course it would be possible to recast much of what has been
already written in the light now displayed to us. But it has
been found easier to present the work in the stages in which it
shaped its course and to introduce this principle much as the
romance-writer produces his climax towards the end of the
story.
The water of In my last word on the subject of permeable and imperme-
scopicity aD ^ e seeds and the contrasts they present, I therefore view the
becomes the whole matter from a different standpoint. Up to now the im-
central point . e '
ofthedis- permeability of seeds has been the most conspicuous feature in
the discussion ; and most of the results obtained shaped them-
selves in one way or another in some relation to this quality.
Here I propose in a few pages to make the water of hygro-
scopicity the centre-point of the discussion. The hydratation
of all living vegetable matter may be thus simply stated. There
is the water that is lost when the materials are allowed to dry
180
THE HYGROSCOPICITY OF SEEDS 181
under ordinary air-conditions, the water of vitality ; and there
is the water that this air-dried material loses in the oven when
exposed to a temperature of 100 C. and subsequently regains
from the air, the water of hygroscopicity. Air-dried vegetable
material, whether living or dead, contains only the water of
hygroscopicity, which in these circumstances is one and the
same with the water-percentage. There is no room for any
more free water in a plant's economy than that which is
included in the water of vitality and the water of hygro-
scopicity. It is the water of hygroscopicity that we are
here concerned with, and we have just seen that in air-dried
vegetable substances this is the water that such materials lose
in the oven. Let us then determine how this principle applies
to seeds.
But before we can apply this principle to seeds it is Thecor-
requisite to determine the correlative of the seed in its pre- [h^seed'with
resting and resting stages with other portions of the plant. othe . r
Manifestly the correlative of the living leaf and the living stem the plant,
is the large soft seed of the ripe fruit before the drying and
shrinking process begins. Manifestly also the correlative of
the dried-up leaf and stem is the same seed after it has com-
pleted its shrinking process and has entered upon the resting
stage. As far as their water-contents are concerned, there is
no difference between the resting seed and the dried-up leaf
and stem, all of them holding only the water of hygroscopicity,
which is driven off in the oven and subsequently regained from
the air. As far as vitality is concerned there is also no differ-
ence. We term the leaf dead and say that the vitality of the
seed is suspended. What is the difference ? There is room
for none.
It is thus clear that the seed's hydratation acquires a new
significance when we allow the .discussion to centre around the
water of hygroscopicity and apply the principle of Berthelot. The logical
This principle raises the whole question of the necessity
of water for the resting seed, and the logical issue is the
denial of its necessity altogether. From this point of view see"
1 82 STUDIES IN SEEDS AND FRUITS
there is no use for any free water in the economy of a seed
that has gone through the normal shrinking and drying
process. With these remarks I would now draw attention
to the contents of the following table, which is intended to
illustrate the hydratation of vegetable substances from this
standpoint.
Comparison One notices at once in the columns on the right side of
contents^" the next table how constant in amount is the water of
leaves, fruits, hygroscopicity (the water of the air-dried tissue) in the living
leaf, fruit, and seed. Stated as a proportion of the living
substance, its amount varies usually between 3 and 6 per cent,
in different cases ; but since its quantity is regulated by
the degree of atmospheric humidity, it is evident that if
all experiments were conducted under precisely the same
conditions, the range of the variation would be much less,
probably only 4 to 5 per cent, for these different parts of
a plant.
It is, therefore, not in the water of the air-dried tissue
(the water of hygroscopicity), but in the water lost by the
living tissue when drying under ordinary air-conditions (the
water of vitality) that the several parts of the living plant
differ from each other. This varies considerably, the range
of the results given in the table being 33 to 80 per cent.
But notwithstanding this variation, the most important sugges-
tion that this table offers to us is that the leaf, the fruit, and
the seed are, as respecting their water-contents, all comparable
in the living condition, the living seed being the soft uncon-
tracted seed, such as we see in the ripe capsule and legume
before drying begins. So, again, these parts of a plant are
all comparable in the air-dried state, the air-dried seed being
the typical resting seed. We cannot consider the seed as a
thing apart and place it in a category by itself. The resting
seed from this point of view is just as dead as the dried leaf.
Both are equally inert vegetable substances, and the only free
water that they both contain is what they yield up in the oven
and gain back from the air. Occasionally in the leaf, and
THE HYGROSCOPICITY OF SEEDS
183
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184
STUDIES IN SEEDS AND FRUITS
The hydra-
tation of per-
meable and
impermeable
resting
seeds.
The resting
seed has no
use for its
water-
contents.
normally in the seed, the life of the air-dried tissues may be
re-kindled, but as air-dried substances they have no life in
them.
Another subject upon which the data of the table throw
light is the contrast in the hydratation of resting seeds of the
permeable and impermeable types. There are four typical
seeds of each kind there referred to, and we see that in
whatever way we state the relation of the water of hygro-
scopicity this contrast is brought out, its proportion in the
impermeable seeds being only about two-thirds of that in the
permeable seeds. The difference as re-stated below is not
very great, but it serves to illustrate the contrast drawn
between these two seed-types from a different point of view
in the earlier chapters. We now see that the ultra-dryness
of impermeable seeds is due to the diminution of the water
of hygroscopicity.
A. In permeable seeds, typified by those of Faba vulgaris,
Phaseolus multiflorus y Canavalia ensiformis^ and Alsculus Hippoca-
stanum, the water of hygroscopicity forms on the average about
6 per cent, of the weight of the moist, living, uncontracted
seed, and about 14 per cent, of the weight of the seed in the
resting state.
B. In impermeable seeds, illustrated by those of Guilandina
bonducella, Entada scandens, Mucuna urens, and Dioclea reflexa^ its
average proportion for the moist, uncontracted seed is about
4 per cent., and for the resting seed about 9 per cent.
And now, in conclusion, let me say that though this treat-
ment of the subject, imperfect as it is in many ways, helps
to clear the problem of the resting seed, its lifeless, inert
condition remains as mysterious as ever. A seed that only
holds the water that it would possess whether or not it
retains the power of germination can owe nothing to this
constituent. Take, for instance, the permeable resting seed
with its water -contents ever varying in response to the
hygrometric changes of the air. It holds more water in a
moist climate than it does in a dry one, and as the experiments
THE HYGROSCOPICITY OF SEEDS 185
of several physicists show, it can retain its germinative powers
after being long in conditions completely water-free. I would
assume that in all experiments where vital processes have been
detected in resting seeds the drying process was incomplete.
The indications of the balance are that the permeable resting
seed, when it has attained a stable weight varying only about
a mean in response to the hygrometric changes of the air,
has no use for the water it contains ; and we may infer the
same for the impermeable seed with its diminished water-
contents. The water of hygroscopicity which the resting
seed alone retains is, as we have seen in the previous chapter,
quite insufficient to induce germination. That it is necessary
for the preservation of the germinative powers is negatived
by the fact that when we have exposed the seed for hours
in a broken condition to a temperature of 100 to 110 C. it
gains back from the air in the course of a week or two all
the water it lost in the oven, and in the case of impermeable
seeds considerably more. As a dead seed, therefore, it holds
at least as much water as it does when preserving its germin-
ative capacity. The water of hygroscopicity belongs to a
plant-tissue, whether living or dead, and this is the only free
water that the resting seed contains.
SUMMARY
(1) The water of hygroscopicity becomes the central point of the
discussion, and it is shown that there is no room for any more water
in a plant's economy than that which is included in the water which
the living tissue loses during natural drying, the water of vitality, and
the water which such air-dried material loses in the oven and subse-
quently regains from the air, the water of hygroscopicity. Such are
the indications of the balance as interpreted by the principle of
Berthelot.
(2) In comparing the water-contents of the leaf, the fruit, and the
seed, it is pointed out that just as they are all comparable in the living
condition, so they can be compared in the natural air-dried state, the
withered leaf with the dried-up fruit-case, and both of them with the
normal resting seed. All of them are inert and lifeless, and if we wish
1 86 STUDIES IN SEEDS AND FRUITS
to contrast them we must look for some other point of difference than
that presented by their water-contents.
(3) It is shown that the permeable and impermeable seed, when
their differences are viewed from this standpoint, may be contrasted as
respects their water of hygroscopicity, which is least in the impermeable
seed and greatest in the permeable seed.
(4) The lesson of the balance is that the true resting seed has no
use for any free water that it holds.
CHAPTER IX
THE REGIME OF THE SHRINKING AND SWELLING SEED
ONE mode of comparing the changes which a seed experiences The relation
in the shrinking, resting, and swelling stages, or, in other the^hree" 1
words, in passing from the pre-resting to the resting con- conditions of
dition, and thence on to the swollen state that precedes
germination, is to compare the relative weights of parts in
the several conditions. In Chapter II we discussed this
subject at length as respects the seed in its entirety. We
will now try to obtain an insight into the details of the
regime of the shrinking and swelling seed, with the balance
again as our guide. Although the view is limited, it is
not without instruction ; and perhaps this is one of the
first attempts to state in terms of weight the correlated
problems concerned with the mysterious resting state, with
that strange shrinking process which even immersion in the
pulp of a watery fruit cannot inhibit, and with that singular
return of the seed by absorption of water to the pre-
resting condition whilst preparing for germination. We
here endeavour to illustrate numerically the changes which
the resting seed has undergone in the shrinking stage and
the changes which it has to undergo when swelling for
germination.
The relative weights of the coats and the kernel in the in the
resting seed will first be dealt with. Though in themselves restin g- seed -
of little interest, they acquire importance when we contrast
187
i88
STUDIES IN SEEDS AND FRUITS
The great
range in the
proportional
weights of
the seed's
coverings in
the resting
state.
them with the same data for other seeds, but more especially
when we compare them with the proportional weights in the
pre-resting seed of the moist fruits, and in the resting seed
swollen for germination. I here append in a tabulated form
my results stated as percentages for about eighty-two species of
plants, arranged in order, the seeds with the smallest proportions
of coverings coming first. The data are given in two tables,
one for leguminous seeds, and the other for seeds of other
orders. For convenience only one value will be referred to
in this discussion, that for the seed's coverings, which I will
term the " seed-coat ratio." Thus, when Iris Pseudacorus is
said to have a seed-coat ratio of 20, it is meant that the
coverings make up 20 per cent, of the weight of the entire
seed.
We notice in these tables that there is a great range in
the proportional weight of the seed's coverings, namely,
from 5 to 69 per cent. The maximum of the range is but
slightly extended in the case of seeds with abundant hairs.
If we were to exclude them altogether we should still
have the hairless seeds of Sapindus Saponaria representing
the maximum limit of 64. But we should be no more
justified in disregarding the hairs of a seed than we should
in leaving out of our calculation the wing-like appendages
of seeds like those of the Mahogany tree (Swietenia) or of
the Moringa tree. It is noticeable that whether we restrict
ourselves to leguminous seeds or to seeds of other orders,
the range is much the same. The leguminous seeds belong
to 39 species and show a variation from 6 to 61 per cent.
The other seeds, which belong to 43 species of 20 different
orders, give a range from 5 to 69 per cent. Since, therefore,
nearly the whole range is to be found with leguminous
seeds, it follows that with seeds of this order there is nothing
distinctive in the proportional weight of the seed's cover-
ings ; and, generally speaking, except in the case of seeds
having a ratio less than 20 per cent., they run fairly well
together.
THE SHRINKING AND SWELLING SEED 189
TABLE SHOWING THE RELATIVE WEIGHTS OF THE COATS AND
KERNELS OF RESTING LEGUMINOUS SEEDS, TAKING THE ENTIRE
SEED AS 100.
Average
Relative weights
of coats and
weight
of a
cernels, taking the
entire seed as 100.
Remarks.
single
seed in
grains.
Coats.
Kernel.
Phaseolus vulgaris (French
13-0
6'2
93'8
Bean)
Phaseolus (tropical species) .
6-5
8-0
92 'o
Pisum sativum (Pea)
6-0
8-5
9i "5
Slightly wrinkled seeds.
7-0
lO'O
90*0
Much wrinkled seeds.
Phaseolus multiflorus (Scarlet -
17-0
12-5
87-5
runner)
Cajanus indicus .
3-0
13-0
87-0
Dolichos Lablab .
4-0
14*0
86-0
Faba vulgaris (Broad Bean) .
3'
14-4
85-6
" Long-pod " variety.
." "
38-0
15-0
85-0
Green Windsor variety.
Cassia fistula
4-0
15-0
85-0
Canavalia ensiformis
25-0
i6'o
84-0
Seeds white.
,, gladiata
45-0
20 'o
8o'o
Seeds brownish -red.
,, (species)
1 8'o
21 '0
79-0
Vicia saliva ....
'3
21 'O
79-0
Bauhinia (species)
4-0
*3'5
76-5
Cassia grandis
9-0
25-0
75-0
Vigna luteola
07
25-0
75-0
Mucuna urens
90*0
26'3
737
Canavalia obtusifolia
I2'0
27-0
73'
Csesalpinia Sappan
IO'O
27-5
72'S
Tamarindus indica
2O'O
28-0
720
Entada polystachya
6-6
28-5
7' '5
Seeds permeable.
Cassia marginata .
lO'O
29 'o
71-0
Abrus precatorius .
i "5
30 "o
70 'o
Erythrina indica .
12-5
30*6
69-4
,, velutina
7 '5
3*4
68-6
Sophora tomentosa
Entada polystachya
2-4
5'
32*0
32-8
68-0
67-2
Seeds impermeable.
Erythrina corallodendron
3'2
33' 1
66-9
Dioclea reflexa
lOO'O
40 'o
60 'o
Entada scandens .
400*0
39-0
6 1 'o
Calliandra Saman
4-0
40*6
59*4
Leucsena glauca .
0-8
46*0
54-0
Guilandina bonduc
50*0
49 'o
51-0
(glabra?) .
60 *o
49-0
51-0
An inland Jamaican
species with oblong
yellow seeds.
Poinciana regia
lO'O
49 '5
5'5
Albizzia Lebbek .
2 '2
50*0
50 'o
Enterolobium cyclocarpum .
I 7 -0
52*0
48*0
Adenanthera pavonina .
47
53 -o
47-0
Guilandina bonducella .
40*0
58-0
42*0
Acacia Farnesiana
2'0
6i'o
39-0
Csesalpinia sepiaria
4'0
61-5
3^5
190
STUDIES IN SEEDS AND FRUITS
TABLE SHOWING THE RELATIVE WEIGHTS OF THE COATS AND KERNELS
OF RESTING SEEDS BELONGING TO OTHER ORDERS THAN THE
LEGUMINOS^E, THE ENTIRE SEED BEING TAKEN AS 100.
Relative weights
Average
of coats and
weight
kernel, taking
Order.
of a
the entire seed
Remarks.
single
as 100.
V
seed in
grains.
Coats.
Kernel.
Tamus communis
Dioscoreae
0-3
S'
95-0
Arum maculatum
Araceae
'7
12-5
87-5
Ipomcea tuberosa . .
Convolvulaceae
25-0
20 '0
80-0
Iris Pseudacorus
Index
7
20 '0
80-0
Canna indica .
Cannaceae
2< S
21 '0
79-0
Mammea americana .
Guttiferae
550-0
*3'5
76-5
Swietenia Mahogani (Ma-
Meliaceae
37
25-0
75 'o
Without wing
hogany)
1 8 and 82.
Citrus decumana (Shad-
Aurantiaceae
4-0
26 'o
74 -o
dock)
^Esculus Hippocastanum
Hippocastanese
130*0
27-0
73-0
(Horse-chestnut)
Anona reticulata
Anonaceae
4-0
27-0
73-0
Citrus Aurantium (Orange)
Aurantiaceae
2-5
28-0
72-0
Ricinus communis (Castor
Euphorbiacese
3-0
28-0
72-0
Oil)
Bignonia (near aequinocti-
Bignoniacese
5'
28-0
72-0
alis)
Hura crepitans .
Euphorbiacese
20 'o
30*0
70*0
Anona palustris
Anonacese
4-0
31-0
69^0
Moringa pterygosperma .
Moringeae
5'o
33-0
67*0
Without wings
30 and 70.
Anona muricata
Anonacese
6-0
34 'o
66-0
,, squamosa
S'
35 -o
65*0
Momordica Charantia
Cucurbitaceae
30
37*5
62-5
Ipomoea dissecta
Convolvulaceae
27
37'5
62-5
Jatropha Curcas
Euphorbiaceae
1 2*0
38-0
62*0
Iris fcetidissima
Iridese
0-8
40 'o
60*0
Bignonia (species)
Bignoniaceae
7'5
40 'o
60 'o
Anona Cherimolia .
Anonaceae
8-0
42 'o
58-0
Ravenala madagascariensis
Musaceae
6'o
42-5
S7'S
Chrysophyllum Cainito
Sapotaceae
I I'D
43 -o
57-0
(Star Apple)
Cardiospermum Halica-
Sapindacese
i'4
43 -o
57-0
cabum
Ipomoea tuba .
Convolvulaceae
S'o
44 'o
56-0
Without hairs
41*7 and 58*3.
pes-caprae .
n
3-0
47 -o
53-0
Without hairs
45-5 and 54-5.
Hibiscus Sabdarifa .
Malvaceae
0-4
47-0
53-0
Thespesia populnea .
3-0
48-7
5''3
Without hairs
48 and 52.
Cardiospermum grandi-
Sapindaceae
2 '5
50-4
49-6
florum
THE SHRINKING AND SWELLING SEED 191
TABLE SHOWING THE RELATIVE WEIGHTS, ETC. continued.
Relative weights
Average
of coats and
weight
kernel, taking
Order.
of a
single
the entire seed
as 100.
Remarks.
seed in
grains.
Coats.
Kernel.
Hibiscus esculentus .
Malvaceae
07
51-0
49 -o
Colubrina asiatica
Rhamneae
0-6
5i7
48-3
Achras Sapota (Sapodilla)
Sapotacese
9'5
53 5
46-5
Luffa acutangula
Cucurbitacese
I 'O
55 'o
45-0
Hibiscus elatus
Malvaceae
0-6
56 'o
44 'o
Without hairs
5 3 '4 and $6'6.
Lucuma mammosa .
Sapotacese
220 'o
56-0
44 -o
Gossypium barbadense
Malvaceae
i '4
57-0
43'
Without hairs
(Cotton)
40 and 60.
Chrysophyllum (species) .
Sapotacese
6-0
59-0
41*0
Calotropis procera .
Asclepiadese
o'z
6 1 'o
39-0
Without hairs
50 and 50.
Sapindus Saponaria .
Sapindacese
13-0
64^0
36*0
Gossypium hirsutum .
Malvacese
1-6
68-7
31-3
Without hairs
44'6 and 55*4.
If, then, we group together the results for all these seeds
of 82 species, we get the following arrangement :
GROUPING OF THE SEED-COAT RATIOS FOR THE RESTING SEEDS OF 82
SPECIES OF PLANTS, THE WEIGHT OF THE ENTIRE SEED BEING
TAKEN AS 100.
Below
20
per cent.
20 to 29
per cent.
30 to 39
per cent.
40 to 49
per cent.
50 to 59
per cent.
60 to 70
per cent.
Total.
Leguminous .
Non-leguminous .
9
2
12
II
8
8
5
10
4
9
2
3
40
43
ii
23
16
5
"3
5
3
Note. The total here is not 82 but 83, as Entada polystachya with its two types of
seeds has been entered twice.
The general
indications
Since just half of the species possess seed-coat ratios
between 20 and 40 per cent, (both inclusive), it is probable that suppHedlbiy
the average weight of the seed-coats would be about 30 per oahYseed
cent., rather below for leguminous seeds and rather above for coat ratios.
1 92 STUDIES IN SEEDS AND FRUITS
seeds of other orders. The ratio may have a generic value in
some cases, as in Erythrina, Guilandina, Phaseolus, and Hibiscus ;
and in others it may vary considerably within the limits of a
genus, as in Anona and Ipomcea^ so that as possible disturbing
influences the one may be set against the other. Whilst
ranging widely in some orders, as in Leguminosae, it may
be comparatively uniform in others, as in Malvaceae and
Sapotaceae. Size has little or nothing to do with the ratio,
excluding very small seeds less than one-tenth of a grain, which
are not here discussed. Looking down the lists, we find large
and small seeds frequently associated on account of the
similarity in their ratios. Thus the seeds of Canna indica and
of Mammea americana have similar ratios, although about 220
seeds of the first will be required to make the weight of a
single seed of the second. So also, if we compare the imper-
meable seeds of the two species of Entada^ we find that their
ratios are not far apart, notwithstanding that at least 80 seeds
of E. polystachya are required to weigh down a single seed of
E. scandens. Then, again, with the two sapotaceous plants,
Lucuma mammosa and Achras Sapota, we notice that the propor-
tional weights of the seed-coats are nearly the same, although
the difference between the weights of a single seed are as 220
to 9*5. Size, of course, goes with weight in all these cases.
The con- In resting seeds the seed-coat ratio is sufficiently constant
seed-coat* C to f rm a character for the species, though, as we have seen
ratio .within above, it may Vary considerably within the limits of a genus.
the limits of ' t ' ' j i i r r
a species. Its constancy tor a species is illustrated in the results tor a tew
plants given below ; but my data do not often lend themselves
for such a comparison, since in determining this relation it was
my usual practice to employ a number of seeds at the same time.
Guilandina bonducella, number of seeds tested 22, range of seed-coat
ratios 53 to 64.
Guilandina bonduc^ number of seeds tested 8, range of seed-coat
ratios 44 to 52.
Entada scandens^ number of seeds tested 5, range of seed-coat ratios
37'7 to 40'5.
THE SHRINKING AND SWELLING SEED 193
Anona muricata, number of seeds tested 1 2, range of seed-coat ratios
31 to 38.
Canna Indica^ number of seeds tested 10, range of seed-coat ratios
18 to 25.
With regard to the influence of variation in size as inter-
preted by weight on the seed-coat ratio in the same species, I
am not able to give many data, as my mode of work rarely
admitted such a comparison. The following results for 22 The influence
seeds of Guilandina bonducella indicate that there is no great
difference. The range of the variation in weight was from
33 to 45 grains, the proportion of the seed-coats being slightly
greater in seeds above than below 40 grains. Thus :
Above 40 grains in weight, average seed-coat ratio 58-5.
Below 57'5-
However, carefully guarded observations on a large
number of seeds of the same age and from the same plant are
necessary for the elucidation of this point.
As respecting the influence of appendages on the proper- The influence
tional weight of the seed-coverings in resting seeds, we will deal
first with hairs and then with wings. In the table subjoined
there are given the data for eight kinds of hairy seeds belonging (A) Hairs,
to three families, Asclepiadeae, Malvaceae, and Convolvulaceas, of
which the two first are especially notable for the hairiness of the
seeds in some genera. The results are arranged in order accord-
ing to the proportional weight of the hairs, commencing with the
seeds where the relative weight is smallest. It is evident that
ordinary pubescence as illustrated in the case of Ipomaea pes-capr<e
adds but little to the weight of a seed. Nor does it make much
difference if a pubescent or puberulous seed, as in the case of
Ipomasa tuba, is bordered by longer hairs at the angles ; but when
these hairs are abundant and woolly, as in the seed of If omasa
peltata, the hairy covering may make up 9 per cent, of the total
weight. The proportions for these convolvulaceous seeds are
probably typical of a good many seeds of other families. The
great development of hairs that we find in some Asclepiads and
in some malvaceous genera is not common in the plant-world.
13
194
STUDIES IN SEEDS AND FRUITS
TABLE ILLUSTRATING THE EFFECT OF HAIRS ON THE PROPORTIONAL
WEIGHT OF THE SEED-COATS IN RESTING SEEDS.
Proportion of
Effect of the
parts, taking the
hairs on the
Aver-
weight of the
entire seed as 100.
relative weight
of the coats.
Order.
age
weight
of a
seed
in
Character and
extent of
the covering
of hairs.
to
to
"u
p
Percentage of
the seed-weight.
grains.
3
pq
O
U
^1
8
M
With
Without
hairs.
hairs.
Thespesia
Malvaceae
3*o
Villous at the
i'6
47-8
50-6
49 '4
48-6
populnea
base and
angles
Ipomoea
Convolvulacese
3-0
Pubescent over
2-8
44*4
52-8
47-2
457
pes-caprae
most of sur-
face
Ipomoea
do.
S'
Puberulous,
4-0
40*0
56-0
44 -o
4i'7
tuba
but villous at
the angles
Hibiscus
Malvaceae
0-6
Villous down
6-0
50*0
44 -o
56*0
53'3
elatus
over all sur-
face
Ipomoea *
Convolvulaceae
i'e
Pubescent, but
Q'O
" w
peltata
j
with abund-
ant woolly
hair at the
angles
Calotropis
Asclepiadeae
O'Z
Terminal coma
22 'O
39-0
39 -o
6i'o
50 'o
procera
with hairs i-
i $ inches
long and
spread out
like a pappus,
the whole
easily carried
by winds
Gossypium t
Malvaceae
i'4
Seed invested
28-5
28-5
43 -o
57 -o
40*0
barbadense
with abund-
ant woolly
hair (cotton)
Gossypium f
do.
1-6
do.
43'S
25-2
3*'3
687
44-6
hirsutum (?)
* The proportional weight of the hairs was alone ascertained.
t In Gossypium (hirsutum ?) the cotton adheres firmly to the black seed, becoming
dirty grey and matted next to the seed. Of the relative weight of the hairy covering
(43'5 P er cent -)> white cotton forms 37*1 and the grey matted portion 6*4.
In G. barbadense the cotton easily separates from the black seed, there being no
adherent covering of matted hairs.
THE SHRINKING AND SWELLING SEED 195
We there have genera, like those of Calotropis and Gossypium,
where the hairs may form a quarter or even nearly half the
weight of the seed ; and, as in one species of Gossypium named
in the table, the hairs may be heavier than the kernel.
In illustration of the effect of large wing-like appendages (B) Wings,
on the relative weight of the seed-coats, I will take the seeds
of three familiar tropical plants, Swietenia Mahogani, Moringa
pterygosperma, and Tecoma stans, the data for which are given in
the following table.
TABLE ILLUSTRATING THE EFFECT OF WINGS ON THE PROPORTIONAL
WEIGHT OF THE SEED-COATS IN RESTING SEEDS.
Weight in grains.
Seed -coat ratio,
Character
Seed and wing.
Coats and wing.
aking the entire
seed as 100.
wing or
wings.
Entire
seed.
Wing
or
wings.
Wing
percen-
tage.
Coats
without
wing or
wings.
Coats
with
wing
or
wings.
Exclu-
ding
wing
or
wings.
Inclu-
ding
wing
or
wings
Swietenia
A terminal
3 '5
0-35
10%
'SS
o'go
7-5
*5-7
Mahogani
oblong wing
as in Pinus
Moringa
Seed round
5'
O'2O
4.,
i '45
1-65
30*2
33 '
pterygosperma
with three
vertical wings
T 1 f c.
Thin flat ob-
O *I C
O*O2 I
11
l ecoma sians
long seed
*T
with margin-
al winggreat-
ly prolonged
at the two
extremities
O "O7O
20 7
Pinus
1. crnnritil OD-
long wing,
5 15
zo /o
but formed
from the
scale, and
not truly
comparable
with the
above
Note. In Pinus the seed is only partially enclosed in the base of the wing, and is
exposed on one side.
196
STUDIES IN SEEDS AND FRUITS
The indica-
tions of the
table.
The wings
of resting
seeds only
serve an
accidental
function.
Withered
leaves and
dried seeds
are in the
same
category.
Excluding the Pine seeds, which are not strictly comparable
with ordinary winged seeds, we observe that in the three types
of seeds here exemplified the weights of these appendages vary
in amount between 4 and 14 per cent, of that of the entire
resting seed. The wings are here greatly developed, so we
may infer that in ordinary " margined " seeds, where the alar
appendage is reduced to a narrow border, there is very little
addition to the seed's weight. Now wings are functionally
useless as we observe them in the resting seed, or we may put
it in another way, and say that though actively functioning
in the soft living seed within the living fruit, they have no
biological significance in the dry seed of the withered fruit.
Being dried up and dead they could only serve an accidental
function in a resting seed which is practically in the same
condition. A more natural comparison of these types of
winged seeds would therefore be obtained by contrasting
them in the living moist condition within the fruit when the
wings are actively functioning organs. In the resting seed
the wings are dead and dried up and could only serve acci-
dental ends.
As far as the capacity for transportal by wind is concerned
the withered leaf and the dry winged seed are in the same
category. That the seed possesses the power of reproducing
the plant is an accident as regards its fitness for wind-
transportal. The puff of wind will carry along both the
seeds that are germinable and the seeds that have lost this
power ; and we cannot distinguish between them as respects
either appearance, weight, or size. Yet the dispersal of
seeds by winds is real enough. The seeds of Tecoma stans,
which are about an inch long, weigh just about the same
as a piece of newspaper cut to the same size. The wind
when strong could carry them great distances, and the like
may be said for the seeds of the Pine. The much heavier
winged seeds of Moringa, as experiment shows, are but little
aided in this way by their appendages. In an ordinary
breeze a Mahogany seed as it falls out of the dried dehiscing
THE SHRINKING AND SWELLING SEED 197
fruit would be transported, as I find, only a few paces ;
but during a strong gust I have known it to be carried a
hundred feet.
In this connection the remarks of Dr Goebel on the Goehel's
" parachute-apparatus " of fruits are well worth quoting, since concerning
they would apply in a sense also to seeds. In his Organo- fruits -
graphy of Plants (English edition, ii. 570), he writes as
follows : " . . . Many arrangements which have hitherto
been considered merely as a parachute-apparatus on the
ripe fruit are in my view to be considered as a trans-
piration-apparatus for the ripening fruit, and these sub-
sequently can be used for distribution, but are not necessarily
for this. ..." However, the function of the wings of
the moist seed in the living fruit would probably be
haustorial. In other words, these appendages would greatly The author's
increase the seed's capacity for absorbing water. In the cernhj"
instance of the moist white seeds of the Mahogany tree the ^attd b"
increase of the area of the receiving or absorbing surface due Mahogany
to the wing is very large, the alar surface-area being more than
double that of the seed, as is indicated in the following
measurements :
Surface-area of the seed without the wing, 450 square millimetres.
wing alone, 1050
winged seed, 1500
In the case of the seed of the Pine it was long ago
suggested by Goeppert, as quoted by Nobbe in his Handbuch
der Samenkunde (p. 49), that the wing exercised the function
of a funicle or umbilical cord.
With the Mahogany seed it is probable that in the closed
living fruit the wing also serves for storage of water. As
shown in the tabulated results of my observations given
below, the wing and coverings of the soft white seed in the
full-grown fruit hold nearly twice as much water as the
kernel, losing about 89 per cent, of their weight in the
drying and shrinking process, as against 49 per cent, lost by
198
STUDIES IN SEEDS AND FRUITS
the kernel. This excess of water in the wing is probably
associated with the watery condition of the fleshy placental
column in the living fruit. It will be seen from the discussion
of the regime of the drying Mahogany capsule in Note 22
of the Appendix that the placental column loses about 70 per
cent, of its weight as the fruit dehisces and dries, the loss of
the capsular walls being about 60 per cent. Thus we find
a regular gradation in the water-contents of a living Mahogany
fruit, viz. about 60 per cent, in the fruit walls, about 70 per
cent, in the placental column, and about 90 per cent, in the
wings of the seeds. We are here referring to the indications
supplied by the loss of weight during the natural drying
process.
THE SHRINKING REGIME OF THE PRE-RESTING MAHOGANY SEED, THAT
IS TO SAY, OF THE SOFT, UNCONTRACTED, MOIST SEED OF THE
FULL-GROWN FRUIT.
(The data required for this purpose are the weights of the pre-resting and resting
seeds and the proportion of parts in each condition. )
Condition of the wing.
Absolute and relative
weights, the first
in grains.
Loss of weight during
the natural drying
of the fruit.
Pre-resting.
Resting.
Pre-resting.
Resting.
Wing and
seed-coats
Kernel
Entire seed
White, heavy,
thick, soft,
and flabby
Brown, light,
thin, and
crisp
8-4 (60)
5-6 (40)
14*0 (100)
0-95 (25)
t'*S (75)
3 '80 (100)
887%.
49%
73%-
The pro-
portional
weights of
parts in the
three condi-
tions of the
seed supply
data for
determining
the regime of
the shrinking
and swelling
seed.
We now pass on to the determination of the proportional
weight of the seed's coverings in the two other conditions
of the seed, the pre-resting state, when the seed attains its
full size in the moist ripe fruit, and the state immediately
preceding germination, when the resting seed has absorbed
much water, and the embryo is on the eve of continuing
its growth that was brought to a standstill during the shrink-
ing process. These data being obtained, we shall possess
THE SHRINKING AND SWELLING SEED 199
the seed-coat ratios for the three conditions of the seed,
the pre-resting, the resting, and the swollen state pre-
paratory for germination ; and in contrasting them we
shall be constructing the regime of the shrinking and
swelling seed, of the seed as it enters upon the rest-
ing period, and of the seed as it subsequently swells for
germination.
It has already been established in Chapter II. that the The return
seed takes up when swelling for germination the water that higseeTto
it lost in the shrinking process, the weight lost during J^^f^ujg
the shrinking being approximately regained during the pre-resting
swelling. But it will be brought out in this chapter that in simple
the attainment of this result the parts of the seed take P rocess -
different shares, the coverings of the swelling seed never
regaining all the water originally lost, whilst the kernel
takes up more water than it held in the pre-resting state.
However, the loss of the one tends to counterbalance the
gain of the other in the following fashion. The deficiency
of the coats is generally larger than the excess of the
kernel ; but since the coats as a rule are only one-half
or one-third of the weight of the kernel, the ultimate
result is usually not much affected. Nevertheless, this is
sufficient to show that the return of the resting seed
when swelling for germination to its original weight as a
pre-resting seed is not a simple process, and that such a
result of experiments can only be regarded as approximate
in value.
In the following table are given the data for construct- The elements
ing the regime of the shrinking and swelling seed in a jngthe
considerable number of cases. Knowing the weight of l^^g
the resting seed, the shrinking and swelling ratio, and the regime,
proportional weight of the coverings (the seed-coat ratio)
in the three conditions of the seed, the determination of
the shrinking and swelling regime for any seed named in
the table can be readily effected, as shown in the example
added.
200
STUDIES IN SEEDS AND FRUITS
TABLE SHOWING THE PROPORTIONAL WEIGHT OF THE SEED'S COVERINGS
(SEED-COAT RATIO) IN THE THREE CONDITIONS OF THE SEED,
THE LARGE, MOIST, PRE-RESTING SEED OF THE RIPE FRUIT, THE
RESTING SEED, AND THE SEED SWOLLEN FOR GERMINATION.
(From the data given in this table the regime of the shrinking and swelling seed can
be readily constructed, as explained in the example given. P. = permeable ; I. = imper-
meable ; V. variable.)
The seed-coat ratio
The
in the three con-
T3
Order.
Average
weight ol
a resting
seed in
shrinking
and swell-
ing ratio,
the weight
of the rest-
ditions of the seed,
the weight of the
entire seed being
taken as 100.
U
S!
IM
O
Ig
8
rt
grains.
ing seed
B
rt
being
c?
_c
S i o
i QJ -X
^J
taken as i.
1-1 '-Z3
to
Pi <8
cnv2'|
Abrus precatorius .
Leguminosse
i-5
2-25
30*0
28-0
V.
Acacia Farnesiana .
, (
2'O
2'OO
59-6
60-8
53*6
V.
Adenanthera pavonina .
ii
47
2-42
...
53'
50-1
I.
^Esculus Hippocastanum
Hippocastaneae
2 '20
35-0
27-0
P.
Albizzia Lebbek .
Leguminosse
2 '2
2-27
50 'o
32-5
V.
Anona muricata
Anonaceae
6-0
i -4 3
33-0
26 '4
P.
Arum maculatum .
Aracese
07
1-63
33 -o
12-5
P.
Bauhinia (species) .
Leguminosse
4'0
2'IO
23-0
Z 3'5
24 'o
V.
Bignonia (near sequi-
Bignoniacese
5'
2-30
38*0
28-0
...
p.
noctialis)
Csesalpinia Sappan
Leguminosse
10*0
2 '2O
3 2 '5
27 '5
26*4
V.
, , sepiaria
M
4-0
2'22
6 1 *o
6 1 '4
53-0
V.
Cajanus indicus
ii
3-0
2'10
28-0
13-0
i6'o
p.
Calliandra Saman .
II
4-0
2-SO
40 '6
35 -o
V.
Canavalia ensiformis
25-0
2-17
i6'o
21-5
p.
, , glad ia ta
M
45-0
2'I I
...
19-8
23-3
V.
,, obtusifolia .
n
I2'0
2^0
45-0
27-0
34-6
V.
,, (species of) .
18-0
21 '0
22-3
V.
Cassia fistula . .
II
4-0
2^0
26*3
I5-0
17'2
V.
,, marginata .
II
lO'O
2*10
28-3
V.
grandis
I)
9-0
Z'H
...
25-0
26 "o
V.
Dioclea reflexa
(A) Impermeable
M
90 'o
2-07
48-5
40 'o
33*5
I.
(B) Permeable seed .
,,
lOO'O
1-86
48-5
38-0
36*1
p.
Entada polystachya
(A) Impermeable
)>
5'
2-50
27-2
32 P 8
25-1
I.
(B) Permeable seed
6'6
2-25
27-2
28-5
24*0
p.
Entada scandens .
II
400^0
2-50
46^0
39'0
31-0
I.
Enterolobium cyclo-
ii
17*0
2-30
46*0
V.
carpum
Erythrina corallodendron
M
3 '2
2-16
33' 1
30-4
V.
,, indica
II
12-6
2-49
...
30*6
28-1
V.
,, velutina .
ii
7'S
2 "40
...
3 I- 4
34-0
V.
Faba vulgaris (Broad
II
30*0
2 '00
33-0
15-0
13-0
p.
Bean)
Guilandina bonduc
"
50*0
2-47
48-7
48-2
I.
THE SHRINKING AND SWELLING SEED 201
TABLE SHOWING THE PROPORTIONAL WEIGHT, ETC. continued.
The seed-coat ratio
The
in the three con-
TJ
Order.
Average
weight of
a resting
seed in
shrinking
and swell-
ing ratio,
the weight
of the rest-
ditions of the seed,
the weight of the
entire seed being
taken as 100.
B
1
grains.
ing seed
n . /-
being
. tjb
B
|B.J
6
taken as i.
o _c
O rt
<u
B
*v2-S
K
C/3 g
Guilandina bonducella
Leguminosse
40*0
3 - oo
60-8
57'8
53 'o
i.
, , glabra (?)
60 'o
2-52
49 'o
44 '4
i.
Hura crepitans
Euphorbiacese
20 "o
2*10
57-0
30*0
44-0
p.
Ipomoea pes-caprse
Convolvulacese
3-0
2-50
55'
47 -o
40 'o
i.
tuba
f>
2-63
46*0
44 -o
32*0
i.
, , tuberosa
M
25-0
2-50
2 I'O
ig'o
V.
Iris fcetidissima
Iridese
0-8
3-10
65-0
40 'o
6o'o
p.
,, Pseudacorus
ii
0*7
2'OO
40*0
2O 'O
25-0
p.
Leucsena glauca
Leguminosse
0-8
2'6o
45-2
46 '2
i.
Luffa acutangula
Cucurbitacese
I'O
77
55'
62*0
p.
Mucuna urens
Leguminosse
90 'o
2'OO
47'5
26-3
20 '4
i.
Phaseolus multiflorus
n
i8'o
2 '00
25-0
I2'S
9-0
p.
Pisum sativum
(A) Smooth seeds
ii
6'o
I '90
25-0
8-5
9-0
p.
(B) Wrinkled seeds *
ii
7-0
2*40
30*0
IO'O
9 '4
p.
Poinciana regia
ii
10 '0
2'3O
45 '5
49 '5
41*0
V.
Ricinus communis .
Euphorbiacese
3'
1-33
28-0
23 'o
p.
Swietenia Mahogani
Meliacese
37
3-70
60 'o
25-0
p.
Tamarindus indica
Leguminosse
20 'o
2-15
28-0
33'
V.
Thespesia populnea
Malvaceae
3'
1-82
37 'o
48-7
45-0
V.
* The collection of water under the coats seriously affects the regime of the
wrinkled seed.
I will take the seed of Entada scandens to illustrate the illustration
employment of the data in the above table for determining ^e
the shrinking and swelling regime of a seed. All that is the table
required are the shrinking and swelling ratios of the entire
seed and the proportional weight of parts in the three
conditions of the seed, the pre-resting, the resting, and the
swollen state. The ratios are given in two ways, one where
the weight of the resting seed is taken as i, the other where
that of the pre-resting seed is taken as 100, the first
method being required for purposes of comparison when,
as often happens, the data for the swelling process are alone
available.
202
STUDIES IN SEEDS AND FRUITS
ENTADA SCANDENS.
(Weight of resting seed 400 grains. Shrinking and swelling ratio 2*5, taking the
weight of the entire seed as i. Pr. =pre-resting seed ; R. = resting seed ; and Sw. = the
seed swollen for germination. )
Proportional
Shrinking and swelling ratios.
weights stated
as a percentage
of the weight of
the entire seed.
Weights in
grains.
Weight of rest-
ing seed as i.
Weight of pre-
resting seed
as loo.
Pr.
R.
Sw.
Pr.
R.
Sw.
Pr.
R.
Sw.
Pr.
R.
Sw.
Coats .
46
39
3i
460
156
310
z'9S
I
1-99
IOO
34
67
Kernel
$4
61
69
540
244
690
2*21
I
2-8,
IOO
4<y
128
Entire
IOO
IOO
IOO
1,000
400
1,000
2- S
I
2-50
IOO
40
IOO
We will commence with the comparison of the regimes
of two types of leguminous seeds, that of Guilandina bonducella
and that of Faba vu/garis (Broad Bean), the first with im-
permeable, the last with permeable coverings. Employing
the data given in the table, we get the following results :
COMPARISON OF THE SHRINKING AND SWELLING REGIMES OF AN
IMPERMEABLE AND A PERMEABLE LEGUMINOUS SEED, TAKING THE
WEIGHT OF THE PRE-RESTING SEED AS 100.
Pre-resting
seed.
Resting seed.
Seed swollen for
germination.
Guilandina bonducella (im- I
permeable) . . .1
Coats
Kernel
Entire
IOO
IOO
IOO
3*
36
33
87
120
IOO
Faba vulgaris (permeable) -{
Coats
Kernel
Entire
IOO
IOO
IOO
23
63
5
39
130
IOO
Note that the pre-resting seed is the soft seed of the full-grown moist fruit.
Illustrations We here see that whilst in both seeds the coats of the
oftheshnnk 6 swe lli n g see( i fail to regain the water lost in the shrinking
ing and process and the kernel ultimately holds more water than
swelling 1,1-1 i i-
seed. it held in the pre-restmg state, there is an important dis-
THE SHRINKING AND SWELLING SEED 203
tinction in their behaviour, the deficiency in the gain of
the coats of the permeable seed being much the largest.
But the difference is only one of degree, since both types
of seeds illustrate the same general principle. There is
much that is extremely suggestive in these figures ; and
if we compare them with those tabulated below which
represent the average results for impermeable, variable,
and permeable leguminous seeds, we perceive that the
regime illustrated by the two type-seeds just dealt with
applies generally to seeds of the family. It is as true of
the individual species as it is of the aggregate. Of the
seventeen species of leguminous seeds, for which complete
data are given in the preceding general table, all but one,
that of Bauhinia, conform to the principle that during the
swelling of the resting seed for germination the coats fail
to regain all the water lost in the shrinking process, whilst
the kernel not only regains all the lost water but absorbs
TABLE GIVING THE AVERAGE SHRINKING AND SWELLING RATIOS FOR
THE COATS, KERNEL, AND ENTIRE SEED OF IMPERMEABLE, VARI-
ABLE, AND PERMEABLE LEGUMINOUS SEEDS.
The impermeable seeds used are those of Dioclea rcflexa, Entada scandens, Entada
polystachya (impermeable type), Guilandina bonducella, Leucana glauca. The variable
seeds are those of Acacia Farnesiana, Bauhtnia, Casalpinia sepiaria, Casalpinia Sappan,
Canavalia obtusifolia, Cassia fistula, Poinciana regia. The permeable belong to Cajanus
indicus, Pisum sativum, Faba vulgaris, Phaseolus multiflorus.
Shrinking and swelling ratios for the pre-resting (Pr.), resting (R.), and swollen
(Sw.) seed stated in two ways, the pre-resting seed being taken as 100 in the first way,
and the resting seed as i in the second way.
Number of
species.
Coats.
Kernel.
Entire Seed.
Impermeable
' I
Pr. R. Sw.
100 39 So
(2-6 i 2-1)
Pr. R. Sw.
100 42 1 18
(2-4 i 2-8)
Pr. R. Sw.
100 40 100
(2-5 I 2-5)
Variable .
' {
too 40 85
(2-5 I 2'l)
100 47 112
(2'I I 2- 4 )
100 44 100
(2-3 i 2-3)
Permeable
i
100 22 42
(4'5 r i'9)
100 60 122
(l'7 I 2'0)
100 50 ioo
(2'O I 2*0)
204 STUDIES IN SEEDS AND FRUITS
considerably more. It is likely that further investigation
may bring the behaviour of the Bauhinia seeds into line
with that of other seeds. It would appear from the table
that as a general rule, although the coats of the per-
meable seed shrink more than those of the impermeable
seed, both double their weight in the swelling process.
On the other hand, the kernels of permeable seeds, though
shrinking less, only double their weight when swelling for
germination, whilst the kernels of impermeable seeds shrink
more and increase their weight threefold in the swelling
process.
It becomes at once apparent from all the tabulated results
that the resting state leaves its impress on the germinating
seed, especially with reference to the behaviour of the coats.
The impress But the impress is also evident in the contrasts in appearance
presented by the coverings in the pre-resting seed and in the
see< ^ sw U en f r germination. In the pre-resting state the
tion. coats are usually thick, moist, fleshy, easily marked by the
finger-nail or cut with a knife, and elastic or yielding. In the
swollen seed on the eve of germination the seed's coverings
are thinner, relatively dry, tough, and unyielding. With a
seed like that of Entada scandens these characteristics are well
displayed, and we may take it as a good example of the
mechanism of germination in seeds of this type. In the
pre-resting or so-called unripe state we have a white, moist,
flabby seed with coats 3 to 4 millimetres thick. In the
swollen, germinating stage we have a dark brown seed with
tougher and drier coverings between 2 and i\ millimetres
thick.
But a more important indication of the impress of the
resting state appears when we compare the changes in weight
with the changes in size. The seed on the point of germi-
nation is usually rather smaller than the so-called unripe
or pre-resting seed. This is brought out in the measure-
ments for four leguminous seeds in their several stages below
given.
THE SHRINKING AND SWELLING SEED 205
MEASUREMENTS IN MILLIMETRES OF LEGUMINOUS SEEDS IN
THE THREE CONDITIONS
Pre-resting
Resting.
Swollen for
germination.
Entada scandens
66-5
47 '5
64
Guilandina bonducella
25-0
1 8'o
Z 4
Csesalpinia sepiaria . .
14-0
IO'O
'3
Canavalia obtusifolia .
21'0
'5'S
20
Taking the case of the disc-shaped seed of Entada scandens,
we find that the embryo or kernel of the seed swollen for
germination is no longer enclosed, as in the pre-resting seed, Thecondi-
in soft, yielding coverings, in which it lies easily, filling the j^rainwithin
space without tension. It is now invested by tough, unyield- the swelling
ing, drier coverings ; and, whilst the kernel has increased its
weight by about 28 per cent, through water-absorption, the
coverings are drawn tighter round it than in the pre-resting
state. As shown in the regime before illustrated, the kernel
that weighed 540 grains in the pre-resting state now weighs
690 grains, and the seed, as we have just seen, is rather smaller.
The strain produced by the swelling embryo within its
tightened coats must be great, and the coverings yield opposite
the hilum, the process being purely physical and not necessarily
followed by germination, itself a purely biological process in
which the active growth of the hypocotyl is involved. The
tension within the seed is well illustrated at times when the
rupture of the coats is from some cause delayed and one or
both of the thick cotyledons within break right across. The
selection of the hilum or scar for the seat of the first rupture
of the coats is on physical grounds not easy to explain, since
the coverings are here thicker than elsewhere ; but this is a
point that is discussed in Note 23 of the Appendix.
The great tension existing within the seed on the eve of
germination is also well exemplified in the regimes of the
three other leguminous seeds, for which measurements have
above been given, viz. Csesalpinia sepiaria^ Canavalia obtusifolia^
2C>6
STUDIES IN SEEDS AND FRUITS
and Guilandina bonducella. The swollen seed ready for ger-
mination is rather smaller than the pre-resting seed of the
ripe moist pod. Its coats are tougher and drier, holding in
one instance 23, and in two instances 13 per cent, less water
than in the pre-resting condition. Yet within these tightened
relatively unyielding envelopes lies in each case a kernel that
is about 20 per cent, heavier through the absorption of water,
and correspondingly larger than in the pre-resting state, a
condition of strain necessarily resulting.
As a rule the conditions of strain within the swelling seed
are at first rather more pronounced in permeable than in imper-
meable leguminous seeds. This is well shown in the average
results for these two types of seeds already given on a previous
page. But in the case of the permeable seed the relatively
thin coverings soon give way, whilst with the impermeable seed
the tougher and thicker coats resist the strain of the swelling
kernel for many days, and the strain, though less at first,
becomes very great when the swelling of the kernel is far
advanced.
It occasionally happens with impermeable seeds that the
conditions of strain are intensified from the beginning, and, as
in the case of the seed of Mucuna urens, a somewhat abnormal
regime is displayed. Whilst its coats behave like those of a
permeable seed, its kernel plays the r61e of a seed of its type,
but in an exaggerated fashion.
The regime of
Mucuna urens
Coats : pre-resting 100, resting 28, swollen for
germination 43.
Kernel : pre-resting 100, resting 70, swollen for
germination 152.
Entire: pre-resting 100, resting 50, swollen for
germination 100.
Whilst studying this seed in the West Indies, I noticed
that the complete soaking of the coats was not requisite for
germination, the radicle often protruding through coverings
partly dry. This occurs occasionally with seeds like those of
Dioclea reflexa and Entada scandens. In some other leguminous
Cassia fistula
Tlauhinia
THE SHRINKING AND SWELLING SEED 207
seeds, usually of the variable type, the tension produced during
the swelling of the resting seed is but slight, as with those of
Entada polystachya and Poinciana regia. In other variable seeds
again, as with those of Cassia fistula, the strain may be great ;
whilst in rare instances, as with the seeds of Bauhinia, there
may be none at all. The case of Cassia fistula is interesting, as
it indicates that albuminous seeds may behave like exalbuminous
seeds in this respect.
' Coats : pre-resting 100, resting 23, swollen for
germination 65.
Kernel : pre-resting 100, resting 46, swollen for
germination 112.
Entire : pre-resting 100, resting 40, swollen for
germination 100.
Coats : pre-resting 100, resting 49, swollen for
germination 105.
Kernel: pre-resting 100, resting 47, swollen for
germination 99.
Entire : pre-resting 100, resting 48, swollen for
germination 100.
This is all that can be said here for the combined shrinking
and swelling regime of leguminous seeds, and the data in the
general table before given must be allowed to tell their own
story in individual cases. The reader can work out for himself
the regime of any particular seed. Should he wish to contrast
the impermeable and permeable types in the same species, he
will find in the cases of Dioclea and Entada that the permeable
seed in its behaviour, strictly speaking, comes between
the two.
But the seeds of other orders may behave like leguminous
seeds when shrinking before entering upon the rest-period
and when swelling previous to germination. What we may
term the convolvulaceous regime, as exemplified in the
behaviour of the two species of Ipomcea illustrated below, does
not seem to differ materially from the leguminous regime,
although the seeds themselves differ much as respects the
albumen, embryo, and other characters. In its conspicuous
The con-
208
STUDIES IN SEEDS AND FRUITS
features it comes near the average regime of a leguminous
impermeable seed as previously given.
The difficulty
of the seeds
of Hura
crepitans.
Additional
data relating
to the
swelling
ratios of the
parts of
seeds.
THE CONVOLVULACEOUS REGIME.
Pre-resting
seed.
Resting seed.
Seed swollen
for germination.
Ipomcea pes-caprse
Coats
IOO
34
73
Kernel ....
100
47
133
Entire
IOO
40
IOO
Ipomoea tuba
Coats
IOO
37
70
Kernel ....
IOO
40
126
Entire
IOO
38
IOO
There are seeds where the shrinking and swelling regime
presents special difficulties, as in the case of those of Hura
crepitans^ the well-known Sand-box tree, belonging to the
Euphorbiaceae. In this instance when the pre-resting seed is
fully matured, the seed-coverings have already lost consider-
ably in weight, whilst the kernel has just attained its maximum
development. We encounter here the same difficulty that we
meet with when following the development of certain fruits,
such as those of Quercus Robur, Barringtonia speciosa, and Cocos
nucifera (Coco-nut), in Chapter XIV. The behaviour of the
seed of Hura crepitans is fully dealt with in Note 24 of the
Appendix and requires no further mention here, except the
remark that, like other seeds with oily kernels, such as those
of Ricinus and Anona^ there is much less water lost in the
shrinking process and regained in the swelling process than is
required by a typical leguminous seed. Evidently oily seeds
have a regime of their own.
We will now utilise the results obtained for the seeds of a
considerable number of plants where the swelling phenomena
were alone observed, and we shall thus obtain a large accession
to our data relating to the swelling ratio of seeds preparing for
germination with especial reference to the respective parts
THE SHRINKING AND SWELLING SEED 209
taken by the coats and the kernel in the process. We have,
in fact, the " swelling " data for the coats and the kernel in
forty-four species, of which all but ten are leguminous, the
residue belonging to a variety of orders, such as Convolvulacese,
Euphorbiaceae, Iridaceae, etc.
Many influences come into play in determining the swelling The dis-
ratios of the coats and of the kernel of the resting seed pre-
paring for germination, influences that are more numerous,
however, with the seed's coverings than with its kernel. In
the case of the kernel there is the relative dryness of that of
the impermeable seed as compared with that of the permeable
seed, and there is the peculiar regime of the oily seed, as in
RicinuSy where the oil seems to take a vicarious part, much less
water than usual being required for germination. In the case
of the coats there is also the relative dryness of the seed-
coverings in typical impermeable seeds ; but this influence is
at times masked in the swelling process of seeds like those of
Mucuna and Dioclea, where the kernel may begin to germinate
whilst its coats are still partly dry. Then we have the diverse
influence of the various textures of the coverings themselves,
influences that are far more diverse than any that could be
offered by the kernel, however much it may vary in consistence,
as indicated by such terms as farinaceous, fleshy, horny, oily, etc.
If we begin by comparing the swelling ratios of coats and The swelling
kernel for all the plants named in the following table, we find k^neUs *
that in just about two-thirds the kernel has the largest ratio. I 1811 * 117 .
J & larger than
But if we except the fact that all the four species of Canavalia that of the
and both the species of Iris are included in the smaller group
where the coats have the largest ratio, there is little that is
determinate in such an arrangement, species of the same
genera being sometimes separated, as in the cases of Cassia and
Erythrina, whilst permeable and variable seeds are more or
less divided between the two groups, the larger group being
made up of the three types of seeds, impermeable, permeable,
and variable. It is not therefore from such an arrangement
that we should expect to be able to frame any definite infer-
210
STUDIES IN SEEDS AND FRUITS
The most
instructive
arrangement
of the
"swelling"
data.
The deter-
mining
influence of
permeability.
ences in this direction, and accordingly I have not burdened
my pages with it, though the reader can construct it for him-
self from the table subjoined, where all the data are grouped
in another fashion.
In order to wrest their story from all these data, I will make
use of another arrangement as given below. Here the seeds
are arranged in two columns. In the first column the seeds
are placed in order according to the amount of the swelling
ratio of the coats, those with the greatest ratio being placed
first. In the second they are placed according to the value of
the swelling ratio of the kernel, those with the largest ratio
coming first. There is nothing definite to be made out of the
arrangement of the seeds in the first column, since permeable,
variable, and impermeable seeds, whether or not we restrict
ourselves to the Leguminosae, are fairly well distributed. On
the other hand, if we turn to the second column, which contains
the data for eleven impermeable, twenty-one variable, and
thirteen permeable seeds, we find that all but one of the im-
permeable seeds occur in the upper half of the column, where
the swelling ratio for the kernel is the largest, and all but one
of the permeable seeds in the lower half, where the ratio is
smallest, the variable seeds being about equally distributed.
We perceive the same contrast between the indications of
the two columns when we compare the places occupied by
seeds when both permeable and impermeable seeds occur in
the same species. Thus with Entada polystachya and Dioclea
reflexa^ the permeable and impermeable seeds come close
together in the column where the seeds are arranged accord-
ing to the amount of the swelling ratio of the coats, but lie far
apart when the arrangement chosen, as in the second column,
is that of the amount of the swelling ratio of the kernel.
Evidently, therefore, although the question of permeability
or of impermeability is largely shaping itself in its influence on
the swelling ratio of seeds, it is an influence that chiefly affects
the kernel. The coats also respond, though in a less degree,
to this influence, but their behaviour is often masked by
THE SHRINKING AND SWELLING SEED 211
TABLE GIVING THE SWELLING RATIOS OF THE COATS AND KERNELS
OF SEEDS, THE WEIGHT IN THE RESTING STATE BEING TAKEN AS i.
(The ratios are arranged in order, the largest being placed first. Permeable seeds
are marked P., variable seeds V., and impermeable seeds I. Leguminous seeds are
denoted by L.)
Swelling ratio of the coats.
Swelling ratio of the kernel.
Iris fostidissima
P.
4-65
Guilandina bonducella
L.
I.
3"34
Canavalia obtusifolia
L.
V.
3-20
Ipomcea tuba .
I.
3''4
Hura crepitans
P.
3-08
Albizzia Lebbek
L.
V.
3 '06
Canavalia ensiformis
L.
P.
2-87
Leucsena glauca
L.
I.
2-98
Cassia fistula .
L.
V.
2-87
Ipomoea pes-caprse .
I.
2-83
Guilandina bonducella
L.
I.
2*75
Entada scandens
L.
I.
2-83
Cajanus indicus
L.
P.
2-59
,, polystachya .
L.
I.
279
Erythrina velutina
L.
V.
Guilandina (species)
L.
I.
274
Tamarindus indica .
L.
V.
2 '53
Calliandra Saman .
L.
V.
273
Iris Pseudacorus
Canavalia gladiata .
L.
p.
V.
2-50
2-48
Csesalpinia sepiaria .
Poinciana regia
L.
L.
V.
V.
271
2^69
Guilandina bonduc .
L.
I.
2-45
Erythrina indica
L.
V.
2-59
Adenanthera pavonina
L.
I.
2-29
Adenanthera pavonina
L.
I.
Erythrina indica
L.
V.
2-28
Enterolobium cyclocarpum
L.
V.
2'57
Guilandina ( species)
L.
I.
2-28
Ipomcea tuberosa
V.
2-56
Ipomcea tuberosa
V.
2-27
Guilandina bonduc .
L.
I.
2-49
Cassia grandis .
L.
V.
2'20
Cassia fistula .
L.
V.
2-44
Calliandra Saman .
L.
V.
2'l6
Entada polystachya .
L.
p.
2-39
Leucsena glauca
L.
I.
2'l6
Acacia Farnesiana .
L.
V.
2-38
Bauhinia (species) .
L.
V.
2'I5
Erythrina velutina .
L.
V.
Ipomcea pes-caprse .
I.
2-13
Abrus precatorius .
L.
V.
2-31
Pisum sativum (smooth) .
L.
p.
2*12
Dioclea reflexa
L.
I.
2-29
Abrus precatorius .
L.
V.
Z'll
Erythrina corallodendron
L.
V.
2-25
Csesalpinia Sappan .
L.
V.
Z'll
Canavalia obtusifolia
L.
V.
2-24
Enterolobium cyclocarpum
L.
V.
2-05
Csesalpinia Sappan .
L.
V.
2-23
Canavalia (species) .
L.
V.
2-05
Mucuna urens .
L.
I.
2'l6
Cassia marginata
L.
V.
2-03
Cassia marginata
L.
V.
2-13
Luffa acutangula
p.
2'OO
,, grandis
L.
V.
2-08
Entada scandens
L.
I.
'99
Bauhinia (species) .
L.
V.
2*08
Erythrina corallodendron
Ipomcea tuba .
L!
V.
I.
98
'9 1
Phaseolus multiflorus
Iris foetidissima
L.
p.
p.
2-08
2-07
r ,
Pomciana regia
L
V.
'9 1
Faba vulgaris .
L!
p.
2-05
Csesalpinia sepiaria .
Entada polystachya .
L.
L.
V.
I.
'9 1
'9 1
Cajanus indicus
Canavalia ensiformis
L.
L.
p.
p.
2-03
L.
p.
89
,, gladiata .
L.
V.
2 '02
Dioclea reflexa
L.
p.
'77
Tamarindus indica .
L.
V.
2'OO
Acacia Farnesiana .
L.
V.
75
Pisum sativum (smooth) .
L.
p.
'99
Dioclea reflexa
L.
L
73
Thespesia populnea .
V.
'95
T,
p
73
Dioclea reflexa
L.
p.
92
Thespesia populnea .
Mucuna urens .
L.
V.
I.
68
'55
Canavalia (species) .
Iris Pseudacorus
L.
V.
p.
88
Albizzia Lebbek
L.
V.
'47
Hura crepitans
p.
68
Phaseolus multiflorus
L.
p.
'44
Anona muricata
...
p.
'57
Anona muricata
p.
1-15
Luffa acutangula
p.
'49
Ricinus communis .
p.
I'lO
Ricinus communis .
p.
'43
disturbing causes, and, speaking generally, they tend to play a
neutral part in the matter. This relative independence of the.
212
STUDIES IN SEEDS AND FRUITS
The indica-
tions of the
table.
coverings is well shown, not only in the general lack of
correspondence of seeds in this respect, but in extreme cases
like that of Hura crepitans^ where the seeds, on account of the
large swelling ratio of the coats, stand nearly at the head of the
first column, and on account of the small swelling ratio of the
kernel are placed nearly at the bottom in the second column.
The run of the data in the above table would therefore
lead us to expect that whilst the coats of permeable, variable,
and impermeable seeds would on the average possess swelling
ratios not far apart from each other, the kernels of these three
seed-types would differ markedly in this feature, the imper-
meable seed displaying the largest, the permeable seed the
smallest, and the variable seed a ratio intermediate in amount.
This expectation is fulfilled in the following tabulated results
of the table, whether for all the seeds or for the leguminous
seeds only, though it is on the indications of the leguminous
seed that we must mainly rely, since the disturbing influences
of different ordinal characters are then eliminated.
TABULATED SUMMARY OF THE PRECEDING TABLE SHOWING THE AVERAGE
SWELLING RATIOS OF THE COATS AND KERNELS OF PERMEABLE,
VARIABLE, AND IMPERMEABLE SEEDS WHEN PREPARING FOR
GERMINATION.
Character
of the
seeds.
Number
of species
tested.
Swelling ratios, taking
the resting seed as i.
Coats.
Kernel.
Leguminous only . . . -{
Permeable
Variable
Impermeable
7
'9
9
2*06
2*20
2*12
2-07
2'35
2-69
Leguminous (35 species) and (
seeds of other orders (io-j
Permeable
Variable
Impermeable
13
21
II
2*22
2-18
2'IO
1-89
2-34
274
Their con- The interesting indications afforded m the tabulated
nection with L . ,
the water- summary just given become more important when we connect
percentage, them with the water-contents of the resting seed as signified
THE SHRINKING AND SWELLING SEED 213
by the loss of weight of the materials when exposed in the
oven to a temperature of about 100 C. We should expect
to find with all three types of seeds, where the swelling ratios
for the coats are not far apart, that the water-percentages for
the seed-coverings would not differ much in amount. We
would also expect in the case of the kernels that where the
swelling ratio is greatest, as with impermeable seeds, the
water-percentage would be lowest ; that where the ratio is
smallest, as with permeable seeds, the water-percentage
would be largest ; and that where it is intermediate in value,
as with variable seeds, the water-percentage would be also
intermediate in amount. These indeed are the actual
results that are represented in the tabulated summary to
be now given as respecting seeds for which all the requisite
data have been obtained. In order to avoid disturbing
influences, the summary is restricted entirely to leguminous
seeds, not to all leguminous seeds, but to exalbuminous
seeds of that order.
TABULATED SUMMARY OF RESULTS SHOWING THE AVERAGE RELATION
BETWEEN THE SWELLING RATIOS OF THE COATS AND KERNELS OF
PERMEABLE, VARIABLE, AND IMPERMEABLE SEEDS AND THE WATER-
PERCENTAGES.
(The swelling ratios are given in the general table in this chapter, and the water-
percentages in the table illustrating the absorptive capacities of seeds in Chapter VI.)
Coats.
Kernel.
Character.
Number.
Swelling
Water-
Swelling
Water-
ratio.
percentage.
ratio.
percentage.
Permeable
4
2 '04
'3'4
2*04
14-9
Variable
4
2'IZ
12-3
2-34
11-4
Impermeable .
6
2-13
II'O
2-61
8-3
The Permeable seeds are Canavalia ensiformis, Pisum salivum, Faba vulgaris,
and Phaseolus multiflorus.
The Variable seeds are Abrus precatortus, Ccesalpinia Sappan, Erythrina
corallodendron, and E. indica,
The Impermeable seeds are Adenanthera pavonina, Dioclea reftexa, Entada scandens,
Guilandina bonducella, G. bonduc, and Mucuna urens.
2i 4 STUDIES IN SEEDS AND FRUITS
We see here that whilst with the coats the differences in
the swelling ratios and water-percentages of all three types of
seeds are small, the differences that do exist are in accord with
the principles laid down in Chapters IV. and VI. Thus, the
coats of permeable seeds have a smaller swelling ratio and a
larger water-percentage than the coats of seeds that are more
or less impermeable. But the difference is small, and it is to
the kernels, where the contrast between the three types of
seeds is pronounced, that we chiefly look for evidence in this
direction. The determination of the amount of the swelling
ratio by the quantity of water held by the seed is fully
established by the behaviour of the kernels, the kernel of an
impermeable seed holding on the average not much more than
half the water held by the kernel of an average permeable
seed, and possessing a much larger swelling ratio. In the
first we have a water-percentage of 8 '3, associated with a
swelling ratio of 2*6 1. In the second the water-percentage
amounts to 14*9, and the swelling ratio to 2*04.
The effect of The effect of oil on the absorption of water by the kernels
oil on the r , , . f ... .. .
absorption of or the seeds preparing tor germination is another point to be
water. referred to. The effect is shown in the small swelling ratio of
such kernels, a fact indicating a relatively small absorption of
water. Such seeds have a regime of their own when swelling
for germination. Ordinary permeable resting seeds, like those
of Canavalia, Faba, Pisum, and Phaseolus, dealt with in the
tabulated summary given above, display an average swelling
ratio for the kernel of 2*04, taking the weight of the kernel of
the resting seed as i. But permeable seeds with more or
less oily kernels exhibit a much smaller swelling ratio. Thus,
the kernels of the seeds of Hura crepitans, Anona muricata, and
Luffa acutangula possess swelling ratios of i'68, 1*57, and 1*49
respectively ; whilst with Ricinus communis the swelling ratio
for the entire seed is only 1*33, as against 2*04 for typical
entire permeable seeds belonging to the four leguminous
genera above named. It will thus be seen that whilst an
ordinary permeable leguminous seed doubles its weight by
THE SHRINKING AND SWELLING SEED 215
absorbing water when preparing for germination, a Ricinus seed
adds only one-third to its weight. It is probable that the
small swelling ratios of many of the seeds mentioned in the
table of the results obtained by Hoffmann and Nobbe in
Chapter II. (Brassica, Raphanus, Cannabis, Cameling Helianthus,
and Pinus) result from the oil in the kernels.
That oil takes the place of water in the kernel is shown when
we compare the water-percentages of the kernels of permeable
resting seeds. In Hura crepilans the water-contents of the
kernel amount to 87 per cent. ; in Ricinus they form 6 per
cent. ; whilst with the kernels of the four leguminous plants
dealt with in the tabulated summary, the water-percentage
ranges between 14 and 16. In the cases of certain Palm seeds
oil plays a prominent part in determining the regime. The
water-percentage is low when the spontaneous drying is
complete. Thus in El<eis guineensis it is 9 per cent., and in the
Coco-nut about 7 per cent., this small percentage of water
being connected with the large amount of oil present.
It will be appropriate here to make a few remarks on the The decrease
decrease in the relative weight of the seed-coats as the seed weight 6 of lv
matures in the ripening fruit. Just as the growth of the coatsfas'the
pericarp is always in advance of the seed-growth, so the growth seed ripens,
of the seed's coverings is always in advance of that of the
kernel or seed proper. Thus with Guilandina bonducella the
weight of the coats of the full-sized soft seed in the mature
moist pod is about 61 per cent, of the total weight of the seed.
A little earlier in the history of the seed's growth it is about
66 per cent., and earlier still, when the seed is not much over
half size and the embryo incompletely formed, it is about 70
per cent. The behaviour of the seeds of the Horse-chestnut
\Msculus Hippocastanum) as they ripen in the capsule well
illustrate this progressive change. When the seed is only
one-fourth grown the coats form 46 per cent, of the weight of
the entire seed, when half size 42 per cent., and when full size
35 per cent. In this connection again let us take the data
afforded by Peas (Pisum sativum) from the same set of plants.
2l6
STUDIES IN SEEDS AND FRUITS
In young seeds weighing about 8 grains (when the coats make
up one-fourth of the seed's diameter) the weight of the
coverings is about 37 per cent, of that of the entire seed.
In the mature soft seeds, weighing 12 grains, the proportional
weight of the coats is reduced to 27 per cent. In all cases, one
may add, there is a further decrease in the relative weight of
the coverings in the resting seed. Taking the approximate
data for the different stages, we obtain the following results :
THE RELATIVE WEIGHT OF THE COATS OF THE PRE-RESTING SEED IN
DIFFERENT STAGES AND OF THE RESTING SEED, STATED AS A
PERCENTAGE OF THE WEIGHT OF THE ENTIRE SEED.
The role of
the embryo
in the shrink-
ing and
swelling
stages of
albuminous
seeds.
Pre-resting seed.
Resting
seed.
\ size.
\ size.
f size.
Full size.
Guilandina bonducella
70
66
61
58
/Esculus Hippocastanum .
46
4Z
35
27
Pisum sativum .
37
27
9
Not the least interesting feature of this discussion relating
to the proportion of parts in the three conditions of the seed
is that concerning the r61e taken by the embryo in albuminous
seeds. I deal here only with types of those dicotyledonous
seeds where the embryo has attained the maximum size
permitted by the limits of the seed. The general subject
of the size and other features of embryos is handled in
Chapter XVIII. Here we deal only with those embryos, with
large, flat, more or less foliaceous cotyledons, that occupy the
length and breadth of the seed and lie usually between two
slab-like masses of albumen. A few of the leguminous seeds
used in this inquiry, viz. those of species of Bauhinia, Cassia,
and Poinciana, have these characters ; and for most of them I
possess the requisite data for the embryo's weight-relation in
the pre-resting, resting, and swollen conditions of the seed.
In addition I have also materials for two euphorbiaceous plants
possessing albuminous seeds with simikr embryos, viz. Ricinus
THE SHRINKING AND SWELLING SEED 217
communis and Hura crepitans. The seeds of the two plants just
named are permeable, whilst those of the leguminous seeds are
variable in this respect. If the kernels of the leguminous seeds
experimented upon were, as is probable in some cases, ultra-
dry, it would only be to a small degree (2 or 3 per cent.),
and not sufficient to materially affect their behaviour. For
practical purposes we may assume that the kernels of all these
seeds attain a more or less stable weight in the resting state.
A singular feature of these dicotyledonous embryos, and
we may say the same of other similar embryos, such as those
of the sapotaceous genera, Achras and Chrysophyllum, is that
they do not display in the resting seed the dried-up, shrivelled
appearance so characteristic of monocotyledonous embryos in
the naturally dried seeds of Palms, Cannas, etc. This is
probably due in part to the difference in form and situation of
the embryos in these two types of seeds. In the dicotyle-
donous seed the embryo lies flat between two slabs of albumen
and contracts with the kernel, leaving no unfilled space. With
ordinary seeds of Palms the embryo lies in an elongated cavity,
which it completely fills in the moist seed, but in the dry seed
it has shrunk away from the walls of the cavity. At all events
the water lost by the embryos of the moist seeds of both types
when drying spontaneously does not differ much in amount,
those of Palm seeds (Cocos, Areca, etc.) losing about 66 per
cent, of their weight, and those of the leguminous embryos
(Bauhima^ Cassia^ Poinciana] 50 to 62 per cent.
We have already dealt with the behaviour of the kernel Differentiat-
in the shrinking and swelling of seeds. Here, then, we are Jhf bdiavlour
going to differentiate in the case of albuminous seeds between fthe
r i i 11 i 11 embryos and
the two components ot the kernel, the embryo and the the albumen,
albumen. Allowing for the crudeness of the method, the
indications of the table below are clear enough. The embryo
and the albumen evidently go fairly well together in the three
conditions of the seed, and consequently in the shrinking and
swelling stages, each of them taking its proportionate share in
the processes. The deviations in opposite directions suffi-
2l8
STUDIES IN SEEDS AND FRUITS
ciently establish this point, and it would be unwise to place
much stress on individual differences. Thus, to take the
swelling ratios, although in Cassia and Ricinus this ratio for the
embryo is rather greater than for the albumen, in Poinciana it
is considerably less, and in Bauhinia it is about the same.
TABLE SHOWING THE BEHAVIOUR OF THE EMBRYO IN THE THREE CON-
DITIONS OF ALBUMINOUS SEEDS, THE PRE-RESTING, THE RESTING,
AND THE SWOLLEN STATE PRECEDING GERMINATION. (All are
leguminous except the last.)
The relative weight of the
embryo, taking the kernel
as 100.
The shrinking and swelling ratios
of the embryo and albumen, the
first for the embryo, the second
in parentheses for the albumen.
Pre-
resting.
Resting.
Swollen.
The pre-resting
state as 100.
The resting
state as i.
Pr. R. Sw.
Pr. R. Sw.
Poinciana regia .
Bauhinia (species)
Cassia fistula
47 '9
42-8
27-1
53'5
45-8
22-4
45 '8 j
46-1 1
24-2
100 45 103
(100 36 113)
100 50^5 106
(100 44-9 93)
100 38 100
(100 49 117)
2'22 2*30
(*78 3''3)
1*98 2'IO
(2-23 2-07)
2*63 2*63
(2-03 2-38)
,, marginata
...
18-3
19-1
2-23
( 2'IO)
,, grandis .
...
H7
16-2 |
2-30
Ricinus communis
5-6
''{
I-6 7
( 1-40
Method of
constructing
the shrinking
and swelling
regime of an
albuminous
seed.
In order to obtain the data summarised in the foregoing
tabular statement a considerable amount of work was done. For
the study of the part played by the embryo in the shrinking and
swelling regime of an albuminous seed of the type before de-
scribed it was necessary to make use of a formula containing the
elements for the requisite determinations, these elements being :
(a) The weight of the resting seed ;
() The shrinking and swelling ratios of the entire seed ;
(c) The relative weights of coats, albumen, and embryo
in the three conditions of the seed, that of the un-
contracted pre-resting seed, the contracted resting
seed, and the swollen seed ready for germination.
THE SHRINKING AND SWELLING SEED 219
The elements for the seeds under discussion are given in
the following table. From its columns we can obtain the
materials for constructing the complete regime of the shrink-
ing and swelling seed in the case of three of the species of
seeds there dealt with, the seeds of Hura crepitans being not
here included, as they present special difficulties which are
treated in Note 24 of the Appendix. In three other cases we
have only the elements in part, namely, those for the determina-
tion of the swelling regime. As an example of how the formula
can be worked, I have appended to the table the complete
regime, as thus indicated numerically, for the seeds of Cassia
fistula. Whilst preparing the tabulated summary given above,
I have had before me the regimes of all the seeds dealt with.
Guided by the example given, the reader, by using the elements
in the following table, can determine the regime for any of
the other seeds.
ALBUMINOUS SEEDS. TABLE SHOWING THE PROPORTIONAL WEIGHTS OF
THE COATS, ALBUMEN, AND EMBRYO IN THE THREE CONDITIONS
OF THE SEED.
(From these data the complete regime can be constructed for the shrinking and
swelling seed. )
Aver-
Shrink-
ing and
swelling
Relative weights, taking the entire seed as 100.
weight
of a
resting
seed
ratio,
taking
the
weight
Pre-resting seed.
Resting seed.
Seed swollen
for germination.
of the
in
grains.
resting
seed
|
a
1
i
in
"rt
e
p
1
in
1
a
I
3
o
p
as i.
U
_a
s
w
O
S
W
O
.Q
1
Poinciana regia .
10
2'3
iS'S
28-4
26-1
49 '5
23-5
27-0
41-0
32-0
27-0
Bauhinia (species)
Cassia fistula
4
4
J.'j
23-0
26-^
44 -o
53'7
33-0
20 '0
15*0
66-0
35-0
19*0
24*0
17-2
62-8
35'
20 '0
,, marginata
,, grandis .
10
9
I'll
29*0
25-0
58-0
64*0
13-0
I I '0
28-3
26*0
58-0
62*0
1 2*0
Ricinuscommunis
3
1-33
28 'o
68'o
4-0
23'0
72*0
5
Hura crepitans .
20
57 -o
38-2
4-8
30*0
bi's
8-5
44-0
4-5
7'S
The seed of Hura crepitans presents special difficulties, its regime being discussed in
Note 24 of the Appendix.
22O
STUDIES IN SEEDS AND FRUITS
CASSIA FISTULA. THE SHRINKING AND SWELLING REGIME OF A SEED OF
CASSIA FISTULA IN ILLUSTRATION OF THE MODE OF EMPLOYING THE
DATA IN THE ABOVE TABLE AS DESCRIBED ON THE PRECEDING PAGE.
Weights in grains.
Shrinking and
swelling ratios,
taking the
pre-resting
state as 100.
Pre-resting.
Resting.
Swollen for
germination.
Coats . ...'.:
Albumen
Embryo
Entire .
2*63
5 '37
2'oo
o'6o
2 '64
0*76
172
6-28
2'OO
P. R. S.
100 23 66
100 49 117
100 38 100
10 '00
4'oo
lO'OO
ioo 40 ioo
SUMMARY
(1) In order to illustrate the shrinking and swelling regime of a
seed, a comparison is made of the relative weights of the coats and
kernel in the three conditions : the pre-resting, the resting, and the
swollen state preceding germination (p. 187).
(2) In connection with the requisite data the proportional weights
of the coats and kernel of the resting seed are first dealt with, results
being given for thirty-nine species of leguminous seeds and for forty-
three species belonging to twenty other orders, including Anonaceae,
Convolvulaceae, Euphorbiaceae, Malvaceae, Sapindaceae, Sapotaceae, etc.
For convenience only one value is generally employed in the discussion,
that of the relative. weight of the coverings, which is termed the "seed-
coat ratio" (p. 1 8 8).
(3) Respecting the great range in the proportional weight of the
coats of the resting seed, it is shown that although the range is
from 5 to 69 per cent, of the seed's weight, nearly the whole of it
is presented by the leguminous seeds, and that the maximum of
the range is but slightly extended in the case of seeds with abundant
hairs (p. 189).
(4) By grouping the results for the eighty-two species, it is found
that the average weight of the coats of the resting seed is about 30
per cent, of the total weight, rather below for leguminous seeds and
rather above for seeds of other orders. Excluding very small seeds,
"size" has little or nothing to do with the ratio (p. 191).
(5) As regards the constancy of the seed-coat ratio within the
THE SHRINKING AND SWELLING SEED 221
limits of a species, it is shown that the relative weight is sufficiently
stable, although it may vary considerably within a genus (p. 192).
(6) With reference to the influence of appendages, such as hairs
and wings, on the proportional weight of the coverings of a resting
seed, that of hairs is first dealt with. Although ordinary pubescence
adds but little to the weight of a seed, a copious covering of long hairs
may increase it by 10 per cent. ; whilst in the case of the great hair-
development occasionally found with seeds, as in certain Asclepiads and
in some malvaceous genera (Gossypiuni), the weight of the hairs may
amount to one-fourth or even to nearly a half of the entire weight
(P- 193)-
(7) Coming to the influence of wings on the weight of the resting
seed, it is shown in the case of Swietenia^ Moringa^ and Tecoma that
the wing or wings may make up between 4 and 14 per cent, of the
total weight. With ordinary " margined " seeds there would be but
little addition to the seed's weight (p. 195).
(8) Discussing the function of wings in the resting seed, the author
points out that they serve only an accidental purpose in aiding dispersal,
and that they have no biological significance except in the actively
functioning soft seed of the living fruit. Withered leaves and dry
resting seeds stand in this respect in the same category. The possession
of wings, he shows, does not always materially assist dispersal. In the
case of Pine seeds and the light seeds of Tecoma stans^ wind may carry
them a long distance ; but Mahogany seeds are usually only carried
a short way ; whilst the seeds of Morlnga pterygosperma are not much
assisted in this respect (p. 196).
(9) With regard to wings in resting seeds, the author adopts the
standpoint taken by Dr Goebel respecting the parachute-apparatus of
dry fruits, namely, that although at times serviceable for their dispersal,
they were not originally developed for this end, but performed quite
a different function in the moist pre-resting seed. As regards winged
Mahogany seeds, the author contrasts the heavy, moist, flabby seeds
of the living, closed capsule with the dry, crisp seeds only one-fourth
of their moist weight of the dehiscing dead or dying fruit ; and he
regards the function of the wing in a seed in the first-named condition
as mainly concerned with the absorption and storage of water, the
absorbing surface being increased threefold and the quantity of water
for the seed's wants greatly augmented (p. 197)-
(10) The proportional weight of the coverings in the two other
conditions of the seed is then considered, and it is pointed out that,
knowing the relative weight of parts (coats and kernel) in all the three
conditions of the seed (pre-resting, resting, and swollen for germination),
we possess the requisite data for determining the re'gime of the shrinking
and swelling seed (p. 198).
222 STUDIES IN SEEDS AND FRUITS
(i i) Although, as established in Chapter II., the seed when swelling
for germination regains approximately the water lost in the shrinking
process, or, in other words, returns to about its original weight in the
pre-resting state, it is shown that this result is in a sense accidental,
since the coats do not win back all the water they gave up in the
shrinking stage, whilst the kernel takes up as a rule considerably more,
the two results going to counterbalance each other in determining the
ultimate swelling weight (p. 199).
(12) The materials for constructing the shrinking and swelling
re'gime for a considerable number of seeds are then tabulated and
explained. Commencing with a typical impermeable and a typical
permeable leguminous seed, it is shown that in both cases the coverings
of the swelling seed fail to regain all the water lost in the shrinking
process, the deficiency being greatest with the permeable seed. On the
other hand, the kernel in both cases ultimately holds more water than in
the pre-resting state. The same principle, it is pointed out, applies
generally to leguminous seeds ; but by the employment of the additional
materials we are enabled to see a little more into the average details of
the processes. As a general rule, although the coats of the permeable
seed shrink more than those of the impermeable seed, both double their
weight in the swelling process ; whilst the kernel of the impermeable
seed shrinks more and increases its weight threefold as compared with
the kernel of the permeable seed, which shrinks less and only doubles
its weight when swelling for germination (p. 200).
(13) It becomes apparent from all the tabulated results that the
resting state leaves its impress on the seed swelling for germination,
especially with regard to the coats. This is also evident in the contrast
in appearance between the drier, tougher, and relatively unyielding
coverings of the seed swollen for germination and the moister, softer,
and more yielding coats of the pre-resting seed. But it becomes
particularly noteworthy when we find that the seed on the point of
germinating is a little smaller than the so-called unripe or pre-resting
seed (p. 204).
(14) The result is that conditions of strain arise within the swelling
seed. Whilst with the pre-resting seed the kernel lies easily within
its coverings, with the swollen seed ready for germination the kernel
holds considerably more water than in the pre-resting state and lies
constrained within its tightened, unyielding coats. Examples of the
strain within the seed thus produced are given, and it is shown that
within its tightened envelopes lies a kernel on the average more than
2O per cent, heavier through water-absorption than in the pre-resting
state. The result is the rupture of the coverings, the process being
purely physical and not necessarily succeeded by germination (p. 205).
(15) That the seeds of other orders may possess a regime similar to.
THE SHRINKING AND SWELLING SEED 223
that of leguminous seeds is brought out for purposes of illustration in
the case of the seeds of the two species of Ipomcea^ which represent the
convolvulaceous regime (p. 207).
(16) The special difficulty presented by the seeds of Hura
crepitans is next referred to. These seeds follow the fashion of some
indehiscent fruits, like those of the Oak (Quercus) and of the Coco-nut,
the seed-coverings losing considerably in weight before the kernel
attains its mature' size (p. 208).
(17) The author then utilises a large amount of data obtained for
seeds where the swelling phenomena of the coats and kernel were alone
observed. The results for forty-four species are thus employed, of which
all but ten are leguminous ; and it is remarked that although in about
two-thirds the kernel has a larger swelling ratio than the coats, there is
no very determinate result in this direction, genera behaving sometimes
consistently and at other times being divided in this respect (p. 209).
(18) In order to wrest their story, another arrangement of these
"swelling" data is adopted, from which it appears that whilst with
the coats the swelling ratios, as respects impermeable, variable, and
permeable seeds, are not far apart, with the kernels the ratios for all
three types of seeds difter markedly from each other, the impermeable
seed showing the largest, the permeable seed the smallest, and the
variable seed a ratio intermediate in amount (p. 210).
(19) It is then elicited that this behaviour of the coats and the
kernel in these three seed-types is to be connected with the water-
percentage of the resting seed, but less in the case of the coats, where
the differences are small, than with the kernels, where the differences
are large, the kernel of an impermeable seed holding on the average
not much more than half the water held by the kernel of a permeable
seed and possessing a much greater swelling ratio. With the kernels
of variable seeds, where the swelling ratio is intermediate in extent, the
water-percentage is also intermediate in amount (p. 212).
(20) Two other points are then referred to, the first being that in
seeds with oily kernels, where the unusually low water-percentage
indicates that the oil supplies the deficiency, the swelling ratio, as in
the case of the seeds of Ricinus^ is also unusually small. The second
is the decrease in the relative weight of the coats as the seed ripens ;
and in this connection it is remarked that just as with fruits the growth
of the pericarp is always in advance of the seed-growth, so with seeds
the growth of the coats is always in advance of the kernel (p. 214).
(21) Having dealt with the shrinking and swelling processes of the
kernel, we now differentiate in the case of dicotyledonous albuminous
seeds between the two components of the kernel, the embryo and the
albumen. The role of the embryo in this connection is now studied.
For this purpose only seeds with embryos possessing large, flat cotyledons,
224 STUDIES IN SEEDS AND FRUITS
and occupying the length and breadth of the seed, are employed, seeds
such as those of Ptindana, Bauhinia y Cassia, Ricinus y and Hura. It is
shown that the embryo and the albumen go fairly well together in the
three conditions of the seed, and consequently in the shrinking and
swelling stages, each of them taking its appropriate share in the
processes (p. 2 1 7).
(22) Such a statement implies that the author, with the aid of the
balance, has been able to construct a complete regime for the shrinking
and swelling stages of a dicotyledonous albuminous seed, not merely
for the seed in its entirety, but independently for all its parts : the coats,
the albumen, and the embryo. The materials for such determinations
are tabulated, and the seed of Cassia fistula is taken to illustrate the
employment of the data (p. 218).
CHAPTER X
THE FATE OF SEEDS AS INDICATED BY THE BALANCE
WE realise from the results of the recent researches of Becquerel Long years
and others that long years are needed for the satisfactory study for the study
of the latent life of seeds, a period, to employ the words of jj
this French investigator, far longer than the time during which
the seeds preserve their germinative powers. This is as true
for the indications of the balance as it is for those of any other
method of physical or chemical research. It is necessary that
the life of the inquirer should extend beyond that of the seed
he is studying ; and too often, as Jodin aptly observes, the
savant who commences such an experiment will never know
the results. This is the spirit in which we should approach
such a difficult subject as the life of the seed, one of the
deepest and most mysterious problems that can occupy the
wits of man. A study, though unfinished, is not altogether
incomplete if we leave it so that others can take it up. There-
fore, although the results given in this chapter are derived
from experiments two to four and a half years in length, they
represent only the beginning of a long series of experiments
which, it may be, someone else may continue after my term
of life has ended.
Yet we have here a record of the start and sufficient
indications to enable us to look a little ahead in the matter.
After seeds have entered upon the resting stage and have
quite completed the process of drying in air, four possibilities
present themselves. As years go on they may either lose or
225 15
226
STUDIES IN SEEDS AND FRUITS
The be-
haviour in
time of im-
permeable,
permeable,
and variable
seeds.
The main-
tenance of
the same
weight by
impermeable
seeds implies
the retention
of their ger-
minative
powers.
gain in weight very slowly, or they may remain absolutely un-
changed, or they may acquire a stable weight subject only
to hygroscopic variation about a mean. A period of a few
weeks or of two or three months is usually sufficient for the
completion of the process of drying in free air. For most
permeable and impermeable seeds this is quite enough, as
is shown in Note 12 of the Appendix, though longer periods
may be occasionally required, as in the case of Mammea
americana^ specially referred to in Note 6, where the drying
was continued for about a year.
Speaking generally, my data show that impermeable seeds
can retain their weight unchanged for at least four years,
excluding such small variations, amounting in the case of
Entada scandens to only about 2~oVo of the total weight,
which are mainly instrumental in their nature. On the other
hand, during the same period permeable seeds, assuming what
we may call " the hygrometric state," display a variation in
weight of 2 or 3 per cent, around a fairly constant mean
in response to the varying humidity of the atmosphere.
Variable seeds again behave in an intermediate but change-
able fashion, the result of their varying proportions of
permeable and impermeable seeds, sometimes approaching
one type, sometimes the other, but usually holding a half-
way position and exhibiting a small hygroscopic range of
i per cent, or less.
Coming first to the impermeable seed, we are justified, I
think, in believing that as long as it preserves the same weight
and is non- hygroscopic it retains its vitality. It enjoys
complete immunity from the dangers of the hygroscopic
reaction, which, if continued through years, must, as M. Jodin
observes, ultimately induce molecular changes and lead to
the loss of germinative capacity in the case of the permeable
seed. The impermeable seed, on the contrary, as long as
it is true to its original weight, is exposed to no such risk.
However, Professor Ewart, in his paper on " The Longevity
of Seeds," contends that " even when perfectly inert a macro-
FATE OF SEEDS INDICATED BY BALANCE 227
biotic seed (that is to say, a long-living seed with more or
less impermeable coats) is subject to slow and gradual molecular
changes and rearrangements, such as take place in glass or
wood in the progress of centuries, and that these changes
cannot take place in the contents of the seed without destroy-
ing the molecular arrangements and groupings requisite for
the restoration of life."
Admitting for argument's sake the force of this contention,
we should be compelled to credit such seeds with the capacity
of retaining their germinative powers for many centuries.
But this seems to me to be hardly a correct comparison.
Glass and wood are at all events exposed to atmospheric
influences, and the last named in particular would be continu-
ously subjected to the hygroscopic reaction. The feature
of the non-hygroscopic impermeable seed is that as long as
its coverings are intact it remains hermetically sealed up and
beyond the influence of atmospheric conditions. If we allow
that such a seed may be expected to retain its germinative
powers as long as it retains its weight, then the question
left to determine is concerned with the duration of its capacity
of preserving its weight unchanged ; and in illustration of
this point there are appended the results of some experiments
on impermeable seeds extending over a period of from two
to four years.
It has already been established in Chapters IV. and VI. that
impermeable seeds weighed from day to day give no indication
of any response to the varying hygrometric states of the air.
The data in the table below given make it plain that these seeds
preserve their non-hygroscopic behaviour from year to year.
Time alone will show how long they will remain in this
irresponsive condition as far as any reaction with their
surroundings is concerned. Although, as pointed out in a
previous chapter, the experiment truest to nature would consist
in burying the seed deep in the soil in a dry climate, still,
these tests in free air go to show that impermeable seeds may
remain for many years in this inert condition.
228
STUDIES IN SEEDS AND FRUITS
THE WEIGHTS OF IMPERMEABLE SEEDS DURING PERIODS OF
FROM TWO TO FOUR YEARS.
The aberrant
behaviour of
an imperme-
able seed is
at once de-
tected by
the balance.
Number
of
seeds.
Length
of ex-
periment
in years.
Changes in
weight stated
in grains.
Proportion of the
change stated as
a fraction of the
total weight of
the seed.
i
4i
301' 8-302*0
ToVtf
i
4i
266* 7-266*9
13S8
4*3
TH7J3"
i
3l
406* 5-406*6
4065
Guilandina bonducella
7
4
306* 6-306*8
1
Adenanthera pavonina
22
3
104* 8-104*9
Ipomoea pes - caprse (with
20
3
41*15- 41-2
hairs) ....
Note. The observations were made at irregular intervals every few months. The
first three seeds of Entada scandens were carried to Jamaica and kept there some months
during the first year, which accounts for their rather larger variation of 0*2 grain ; but
in the last three years in England the weighings only varied 0*1 grain. A pebble of
quartz would probably have behaved in the same way ; and evidently the cause of the
variation is largely instrumental. This is also true of Guilandina bonducella. The
samples of the seeds of Adenanthera pavonina and Ipomcea pes-capm were small in
weight ; but the results give the same general indications. In connection with the last-
named it is shown on page 169 that its pubescent hairs have a very slight disturbing
effect.
However, although this is the rule, cases of failure are not
infrequent, and their aberrant behaviour is at once detected by
the balance. Some slight defect in the coats, due probably
to some imperfection in the shrinking process, gives time
its opportunity ; and the seed within, brought into relation
with its surroundings, responds to the changing atmospheric
conditions, first slowly and then more rapidly, until it assumes
the r61e and the limited life-duration of a permeable hygro-
scopic seed. The manner in which this change of state is
carried out has been described in Chapters IV. and VI. in
connection with the results of puncturing or filing the seed-
coverings. The seed gradually gains weight in the course of
months, taking up from the air the water which it previously
lacked ; and, as is shown in the case of filed seeds of Guilandina
bonducella^ it may retain its germinative capacity for two years
after it has virtually lost the protection of its coats, an event,
FATE OF SEEDS INDICATED BY BALANCE 229
however, only possible when kept in a dry room. A
punctured seed in nature would soon fall a victim to the
attacks of mould and insects, unless it germinated quickly.
The failures amongst the impermeable seeds are, as one The failures
might expect, very instructive. We can trace the slow
progress of the loss of impermeability in seeds gathered by
ourselves from the plant. In the course of an experiment senting per-
i j i j 11 i meabihtyas
covering years, a single seed in a sample gradually begins a quality by
to fail, a change unerringly indicated in the balance by the deault
increase of weight. Two seeds of Entada scandens^ the
shrinking process of which I had watched after collecting them
in the immature, uncontracted state, preserved their weight
unchanged for a few weeks, and then began slowly to gain
weight, until at the end of a year each had added 3 per
cent, to its weight. After this they behaved hygroscopically,
like ordinary permeable seeds. The explanation was supplied
in the development of fine cracks in the cuticle. In another
case three seeds, also of Entada scandem^ which together
weighed 1080 grains, gained i grain during the first year.
By subsequently weighing them separately the culprit was
discovered, two of the seeds remaining quite unchanged in
weight. The cause of failure in one of the seeds lay in an
imperfection of the cuticle. The same thing occurred during
an experiment on six seeds of Guilandina bonducella weighing
in all about 200 grains. A gain in weight of i per cent,
during the first year led me to weigh them separately, and it
was thus discovered that this increase was due entirely to one
seed, which on close inspection showed defects in the outer
coat.
The above experiences of faulty impermeable seeds show
that nature fails at times in endowing a seed with imperme-
ability, but the suggestive implication is that in such failures
permeability is presented to us as a quality by default.
Although the indications supplied by my numerous Prof. Ewart
experiments seem clear and unmistakable with reference to the the imperme-
ultimate fate of the impermeable seed, the views held by ablese e d -
230
STUDIES IN SEEDS AND FRUITS
The Acacia
seed.
Old seeds
and in-
organic sub-
stances.
Professor Ewart respecting the matter are opposed to the
position adopted in this work. It has been established by my
observations that the impermeable seed, more especially the
leguminous seed, holds much less water in the entire state than
when broken up and exposed to the air. The process of the
change is exhibited when the seed develops some defect in its
coverings or when we imitate such a defect by puncturing
the coats. The seed then slowly gains in weight by abstracting
moisture from the air, until in time it assumes the stable
hygrometric condition of an ordinary permeable seed.
Now, Professor Ewart takes a very different position. In
the case of Acacia seeds, which are notable for their imperme-
ability, and often contain less than 5 to 8 per cent, of water, he
writes that " such seeds when preserved in a dry atmosphere
seem to steadily lose water, until ultimately as dry as if kept in
a desiccator " (Proceedings of the Royal Society of Victoria^ vol.
xxi. p. 199, 1908). This is based on the fact that old seeds
lost less weight in the oven than fresh seeds. Fresh air-dried
Acacia seeds, he says, contain 5 to 14 per cent, of moisture ;
seeds ten to twenty years old contain from i to 3 per cent. ;
whilst fifty-year-old seeds hold less than i per cent., losing
only O'7 per cent, of their weight after the prolonged exposure
of a day to a temperature of 1 10 C. Fine capillary glass tubes,
he writes, show a greater loss of weight than this, and hence
he infers that " old, dry, cuticularised macrobiotic seeds become
drier than corresponding inorganic material."
Professor Ewart thus observes that in course of time Acacia
seeds become as dry as if kept in a desiccator, and implies that
they behave like inorganic material. This raises the question
as to the behaviour of these two types of substances after
desiccation. Seeds that have been exposed to such a low
temperature that the free water has been completely expelled
fall to powder when struck with a hammer and quickly absorb
the hygrometric water from the air (P. Becquerel, in Annales
des Sciences Naturelles^ Botanique, tome v., 1907). This is
but an extreme form of what occurs in the kernel of an
FATE OF SEEDS INDICATED SY BALANCE 231
impermeable seed when its coats are broken. Being normally
in a state of partial desiccation, it at once begins to supply
the deficiency by absorbing moisture from the air. From
inorganic substances like glass, we should look for no such
behaviour. They have little or no water to lose under
desiccating conditions, and in consequence have little or no
water to regain. This matter is discussed in Chapters VII.
and VIII. It will be there seen that Berthelot lays stress on
the contrast in behaviour between inorganic substances (like
porcelain and metals) and plant-tissues, the first drying com-
pletely in air, whilst the second do not.
There is nothing to lead us to expect that the kernels The kernels
of seeds of any type would ever lose their capacity for meableseeds.
behaving hygroscopically and become non-hygroscopic, inert
substances like porcelain and metals. If this were the case,
Berthelot's principle of reversibility would lose much of its
significance. It must, however, be admitted that the semi-
stony consistence of the kernels of some old permeable seeds
would at first sight seem to justify such a belief. At one time
I thought that the seeds of Msculm Hippocastanum (Horse-
chestnut) and of the Acorn (Quercus Robur) would in time
assume some of the characters and behaviour of inorganic
material, such as chlorite and opal, as regards the diminished
water-contents and the small hygroscopic reaction ; but this
proved to be incorrect. As regards hygroscopicity, reference
has already been made to the effect of time on the behaviour
of the seeds of the Horse-chestnut in their coats, the results
of the experiments being tabulated in Chapter VII. We
saw there that, whether six months or thirty months old, the
hygroscopic reaction was much about the same, namely, 2*0 to
2*4 per cent. Whilst writing these remarks I have conducted
another experiment on the same seeds three or four years
old ; but in this case the seeds were first bared of their
coverings. The three-year-old seeds give a hygroscopic range
of 2 '4 per cent., and the four-year-old seeds of 3*5 per cent.
So also with reference to the bared seeds of the Acorn. I find
232
STUDIES IN SEEDS AND FRUITS
Quercus
Robur.
jEsculus
Hippo-
castanum.
Grias
cauliflora.
that two-year-old seeds display a range of 2*0 per cent., and
three-year-old seeds i'6 per cent.
Respecting the diminution of the water-contents in time in
the case of the kernels of permeable seeds, I will first take those
of Quercus Robur. Here the kernel in the course of time
assumes a chocolate-coloured, semi-waxy appearance and almost
a stony hardness, changes which begin at the periphery. Of
kernels fourteen months old about a third were completely
affected. In another third half of the kernel had undergone
the change ; whilst in the remaining third the transformation
was either in its early stage or scarcely noticeable. Here a
mixed sample of the kernels proved to contain 11*3 per cent,
of water. Every seed in samples two years old and more
displayed the change completed, the water-percentage in
kernels two years old being 13*2, and in kernels three years
old 12-2.
So with the old seeds of Msculus Hippocastanum, it was
found that at least for the first three or four years there was
no diminution in the water-contents. Seeds bared of their
coverings exhibited a water-percentage of iy6 when eleven
months old, 14*4 when twenty-six months old, 12*6 when three
years old, and 13*8 after being kept for four years. These
seeds, it may be added, do not discolour with time like the
seeds of Quercus Robur. As is well known, the seeds of the
Oak only retain their germinative capacity for a few months.
With those of the Horse-chestnut the period, as shown in
Chapter XVIII., is still less.
Now and then one comes upon old seeds that are as hard
and seemingly as dry as a stone, seeds that might almost
be taken for fossils, yet in the oven they prove to contain 10
or 12 per cent, of water. The old seeds of Grias cauliflora,
the Anchovy tree of Jamaica, a myrtaceous tree that flourishes
in the lower courses of rivers in the West Indies, offer con-
spicuous examples. A very remarkable alteration in texture
takes place in the seeds after their death, when the conditions
are dry, as on beaches, where they are stranded in quantities.
The fleshy, though tough living seed, has the singular structure
presented by the seeds of some other myrtaceous trees, such
as Barringfonia, where an enlarged hypocotyl, invested by a
thick rind and forming the storehouse of the food-reserve,
constitutes the seed. As the seed dries it becomes as hard as
a stone, and on section displays the appearance of a fossil fruit,
these stone-like seeds being usually i to i-^ inches long. Yet
on testing the water-contents of one of these old seeds, which
must have been at least six or seven years old, and had been
almost five years in my possession, I obtained a result of 1 2 per
cent., almost all the water lost in the oven being subsequently
regained from the air in the course of a few weeks. I may
direct the attention of the botanist engaged in microscopical
and chemical research to these remarkable changes in the seeds
of this plant. Sometimes a portion of the seed rots, whilst
the other portions experience the change ; and when such a
seed is found in the early stage of transformation, a very
puzzling structure is displayed.
Similar questions might be raised with reference to the Barringtonia
condition of old seeds of Barringtonia speciosa, which possess the
structural features above described in the case of the seed of
the Anchovy tree. The seeds do not become quite so hard
with time, but are sufficiently altered to cause one to look
twice in order to be assured that one is not dealing with some
non-vegetable substance. Yet old kernels collected three
years before lost 10 per cent, of their weight in the oven,
and in a few weeks returned almost to their original weight by
replacing the lost water with moisture abstracted from the air.
There is, however, an indication in my experiments on
impermeable seeds that might seem to point in the direction
of the change in seeds as interpreted from Professor Ewart's
point of view. In Chapter IV. it is shown in the case of bared
kernels of Guilandina bonducella that whilst freshly bared Guilandina
kernels added 13*4 per cent, to their weight in five days, this on uce
excess was reduced to 7*3 per cent, in three months, and to
3 or 4 per cent, after a year, an excess which was retained
2.34 STUDIES IN SEEDS AND FRUITS
during the next twelve months, when the experiment ended.
I did not finally test the water-contents, but the fact that in
the last year the seeds exhibited a hygroscopic variation of 1-4
per cent, indicates that they must still have held a fair amount
of water. But against this indication of Professor Ewart's
view must be placed the indications of another experiment
on the same seeds, the results of which are also tabulated in
Chapter IV. Here I merely filed through the impervious
shell, and thus enabled the air to have access to its ultra-dry
kernel within. During four months the seed slowly added to
its weight as much as 1 1 per cent. ; but at the end of the
experiment, which covered two years, the seed was still about
8 per cent, heavier than before its shell was filed through.
Possible However, a solution of the difficulty seems to be offered
the difficulty, by Professor Ewart's remark, when discussing the drying in
time of Acacia seeds, that " it is as though the cuticle allowed
traces of water to escape externally, but none to enter " (ibid. t
p. 199). From this I am inclined to think that his oven-
experiments for testing the water-contents were carried out on
the seeds whilst protected by their hard, impervious coats. If
so, this explains the whole matter. In my experiments on the
impermeable seeds of Entada scandens and Guilandina bonducella^
which are described towards the close of Chapter VI., I show
that when exposed both in the entire condition and in the
broken condition to a temperature of 100 to 110 C. for two
hours, the seeds in their hard coverings lost only about a
fourth of the water lost by the seeds no longer protected by
their coats. It was also elicited that the seeds in their cover-
ings subsequently made little or no attempt to regain the
moisture from the air and doggedly maintained their imper-
meability. Thus Professor Ewart's surmise that the coats of
a seed allow the water to escape, but inhibit re-absorption, is
certainly applicable to the behaviour of an impermeable seed
during and after the oven test. But this does not reproduce
the conditions of drying at ordinary temperatures in the course
of years.
FATE OF SEEDS INDICATED BY BALANCE 235
Nearly all his results relating to the diminution of the
water-contents of Acacia seeds when kept for years can be
explained on the assumption that the oven-experiments were
made on seeds in their coverings. The fact that the fresh
air-dried seeds sometimes hold as much as 14 per cent, of
water sufficiently indicates that the shrinking process was not
always complete, and that, as his general table also indicates,
they included some permeable seeds, thus accounting for the
greater loss of water in the oven. I am inclined to think that
the low water-percentages of his old Acacia seeds were due to
the experiments being carried out on seeds in their impervious
coverings.
The protection a seed receives from its coats in the oven
was not only exhibited in other experiments on impermeable
seeds, as in the case of those on the seeds of Canavalia obtusi-
folia discussed at the close of Chapter VI., but it was well
displayed by the differences in behaviour of permeable seeds,
when subjected to the oven test in the entire and in the
divided condition, as shown in the results tabulated towards
the end of the same chapter. After an exposure of two hours
to a temperature of 100 to 110 C., the entire seeds of Pisum
sativum, Faba vu/garis, and Phaseolus multiflorus lost 10 or 11
per cent, of their weight, whilst seeds of the same set which
had been cut across lost 14 or 15 per cent. In the first case
the seeds were completely covered by their coats, and in the
last case only in part. The seeds were in all cases eight to
ten months old.
It is on these grounds that I venture to differ from Professor
Ewart. The future inquirer must decide between us.
The hygroscopic variation offers a special difficulty in the Permeable
examination of the effect of time on the weight of a permeable
seed. Notwithstanding that my experiments extend over
periods of three to four years, it is only safe to say at present the first three
11 i -11 i i i'ii or four years,
that the seeds are still m the hygrometric state which they
assumed when first entering the resting stage, exhibiting a
variation about a mean between the several weighings of about
236 STUDIES IN SEEDS AND FRUITS
2 or 3 per cent., being lightest in the summer and heaviest
in the winter months. Variable seeds, where there is a
mixture of permeable with impermeable seeds, display about
half this variation, namely, i per cent. But, as has been
said, the disturbing influence of the hygroscopic reaction is
a great obstacle in detecting small differences in such ex-
periments. If there has been a change, it has certainly not
involved any increase in the average weight. On the contrary,
the indications, such as they are, point slightly in the direction
of a diminution ; but it will not be possible to obtain definite
results until the experiments have been greatly prolonged and
one is able to eliminate the effect of the hygroscopic reaction
by comparing the averages for groups of years.
In such experiments on hygroscopic seeds it is necessary
that they should always be kept in the same room. So
sensitive were my seeds to change that a transference from
one room to another was sufficient to cause a variation of
The experi- l or even of i per cent. Several years ago MM. Van Tieghem
Tieghem * * an d Bonnier published some interesting results in a paper in
and Bonnier. t ^ e ft u u et i n de la Sodete Botanique de France (tome xxix. 1882),
some of which bear directly on the effect of time on the weight
of permeable seeds. They found that after two years in free
air, peas had gained about i^- per cent, in weight, haricots
about 2 per cent., seeds of a species of Vida about i per cent.,
and Ridnus seeds rather more, but the actual increase in the
last case is not given. From my own observations it would
appear that this rise in weight was within the ordinary
hygroscopic range, and that if weighed at another season all
the seeds might have displayed a decrease instead of an
increase in their weight.
As indicated in Note 25 of the Appendix, the variation
in weight of completely air-dried seeds of Pisum sativum,
Faba vulgaris, and Phaseolus multiflorus during a period of
nearly fifteen months ranged from 2'6 to y6 per cent, of the
seed's weight. The variation in weight is also there given
for the seeds of Ridnus communis in the case of experiments
FATE OF SEEDS INDICATED BY BALANCE 237
extending over three years and nearly two years, the amount
of the change being n to 1-6 per cent, of the total weight.
In all cases the seeds were heavier at the beginning than at
the end, a result due to their being kept at first in a damp
room. The variation is the normal hygroscopic reaction.
There is no sign of any permanent increase in weight. If
one was guided only by the run of the figures and disregarded
the conditions of the experiment, one might infer that these
seeds lose weight as they get older.
The permeable and variable seeds now under observation The author's
with the object of testing the influence of time on their ig S e xpen-~
weight belong to nearly thirty genera, of which one-third ments -
are leguminous, and include Abrus, Achras, Anona, C<gsalpinia,
Canavalia, Citrus, Datura, Erythrina, Faba, Hura, Iris, Luffa,
Morinda, Phaseolus, Pisum, Ricinus, Thespesia, etc.
In conducting all experiments of this kind it is, as already Whilst with
remarked, a matter of necessity that the seed should have sSTrfrufts
acquired a stable weight, either as an impermeable seed when, the s <r ed s
with regard to the hygroscopic reaction, it is absolutely inert, complete the
or as a permeable seed when it displays a small variation on
' either side of a mean. It is not merely requisite to employ
resting seeds for the purpose, but they must be resting seeds tached, the
with a stable weight. The seeds of the berry and of the legume moist, fleshy
when first liberated by the opening or by the decay of the half of^heir
fruit are, as described in subsequent chapters, in very different w ^ght after
stages of drying. In both cases the seed may in colour, liberated
hardness, and other features have the appearance of a normal
resting seed. Yet if it belongs to a berry it has still to lose
40 or 50 per cent, of its weight by drying in air ; whilst if
it belongs to a legume it will have already practically completed
the drying process. It is true, as shown below, that legumin-
ous seeds usually lose slightly in weight after being gathered
from the dehiscing pod ; but here we must often be anticipating
nature a little. I have not many observations bearing on this
point, but they are sufficient for the purpose of illustration.
With regard first to the impermeable seeds of legumes, my
238 STUDIES IN SEEDS AND FRUITS
observations indicate in the case of those of Entada scandens
that resting seeds, weighing about 400 grains when removed
from the pod, may lose about 2 grains during the next
few weeks whilst exposed to the free air. Most of this small
loss is probably connected with surface moisture, since Entada
pods break up into closed joints from which the seed has to
be removed. In the cases of the pod of Guilandina bonducella^
which dehisces usually in full exposure to the sun, it would
be unlikely that seeds after lying in the gaping pod under
such conditions would not have completed the drying process.
Coming to permeable seeds of dehiscing pods, I will cite
the case of those of Canavalia ensiformis, which in ten days
after collection from the pods lost about 8 per cent, of their
weight and then entered the stable hygrometric state. Then,
again, the seeds of Csesalpinia sepiaria^ which are in some cases
permeable and in others impermeable, lost about 10 per cent,
of their weight after being gathered from the opening pod.
In both these instances of permeable seeds it is highly probable
that nature was to some degree anticipated, and that, left alone,
they would have completed their drying before detachment
from the pod.
However, the loss of weight experienced by resting seeds
require or seed-like fruits after they have been collected is often far
"airing" more considerable than in the leguminous seeds above cited,
before being
stored. As Nobbe puts it (p. 382), the process here involved is
what the agriculturist would term " sweating " in the case of
wheat, and what the forester would call " airing " when gather-
ing acorns, chestnuts, and maple fruits for winter storage. My
experiments on Acorns (Quercus Robur] and on the seeds of the
Horse-chestnut (^Escu/us Hippocastanum) indicate that they
have still much moisture to lose when they are first detached
in the " browned " condition from the tree. The Horse-
chestnut seed, as it lies on the ground freshly liberated from
its fruit, has still to surrender one-third of its weight in
moisture to the air before its drying process is complete.
The Acorn also, when in the early stage of browning it falls
Seeds that
"sweat" or
FATE OF SEEDS INDICATED BY BALANCE 239
from the cupule, has yet one-fourth of its weight to lose
during its drying. Though leguminous seeds as they escape The after-
from the withered pod have practically completed the drying se ^^>f
process, it is very different with the seeds of watery or fleshy fleshy or
r i r i r i r i wateryfruits.
fruits when they are treed, as must orten happen, rrom the
moist fruit. As the result of a number of observations I
found that after removal from the ripe fruit, and before enter-
ing upon the air-dry condition of the normal resting seed, the
seeds lost weight as shown below :
(a) The seeds of the Apple (Pyrus Malui) lost 45 per cent, of their
weight.
(Z>) The seeds of the Bread fruit (Artocarpus incisa] lost 55 per cent.
of their weight.
(c) The seeds of Momordica Charantia lost 30 per cent, of their
weight.
(d) The seeds of Tamus communis lost 44 per cent, of their weight.
(e) The seeds of the Honeysuckle (Lonlcera) lost 42 per cent, of
their weight.
(f) The seeds of Arum maculatum lost 49 per cent, of their weight.
(g) The seeds of the Shaddock (Citrus decumand] lost 40 per cent, of
their weight.
(/z) The seeds of Genipa clusiifoha lost 43 per cent, of their weight.
(/) The seeds of Opuntia Tuna lost 45 per cent, of their weight.
Before quitting this subject of the drying of seeds after their
liberation by nature's means or after their collection by man, I
would refer the reader to Note 12 of the Appendix for further
details ; but in many ways this stage of the drying process is
linked with other processes dealt with in other chapters.
SUMMARY
(1) For the satisfactory study of the latent life of seeds, says
Becquerel, the experiment ought to cover a period far exceeding that
of the duration of the seed's germinative capacity (p. 225).
(2) The author's investigations into the changes in weight that
seeds experience during the first three or four years after their assump-
tion of a stable weight in the drying process give the following
indications. The impermeable seed preserves its weight and shows no
hygroscopic reaction throughout that period ; whilst the permeable
2 4 o STUDIES IN SEEDS AND FRUITS
seed remains always in the same hygrometric state, and retains the
same average weight, showing only fluctuations of i or 2 per cent, on
either side of a constant mean (p. 226).
(3) As regards the impermeable seed, it is urged that as long as it
preserves its weight and is non-hygroscopic, we may assume that it
retains its germinative powers (p. 226).
(4) The constancy of the weight of impermeable seeds during a
period of three or four years is then illustrated in a tabular form
(p. 228).
(5) The failures in impermeable seeds are at once detected by the
balance. They are instructive in their presentation of permeability as
a quality by default, the impermeable seed owing to some defect in its
coats gradually gaining weight and slowly assuming the role of a
permeable seed (p. 229).
(6) Reference is made at some length to the very different view of
the ultimate fate of the impermeable seed held by Professor Ewart.
In the case of Acacia seeds he considers that in the course of years
they become as dry as corresponding inorganic material, and may hold
less than i per cent, of moisture. This view is controverted, and an
explanation of its origin is suggested (p. 230).
(7) It is shown that in all experiments on the weight of permeable
seeds extending over some time, the disturbing effect of the hygroscopic
reaction, involving as it does a variation of 2 or 3 per cent, of the total
weight, presents a great obstacle to the detection of small differences.
For this reason, therefore, the experiments should cover many years
(P- 235).
(8) It is considered that the increase in weight of i to 2 per cent,
recorded by Van Tieghem and Bonnier, in the case of seeds of peas,
haricots, vetches, etc., after a two years' experiment, comes within the
ordinary hygroscopic range and does not necessarily imply an increase
in the average weight (p. 236).
(9) With the object of testing the influence of time on seed- weight,
the author began four years ago a series of experiments on the seeds of
nearly thirty genera, the intention being to continue them for many
years (p. 237).
(10) The necessity in weighing experiments extending over long
periods of first selecting seeds that have completed the drying process
is pointed out (p. 237).
(n) In this connection it is shown that whilst some seeds, as those
of leguminous pods and of similar dehiscent fruits, are almost completely
air-dry when liberated naturally from the fruit, others from fleshy or
watery fruits have still 40 or 50 per cent, of their weight to give up to
the air. Seed-like fruits, as grains of cereals and acorns, have to submit
to a "sweating" or "airing" process before storage (p. 238).
CHAPTER XI
A CLUE TO THE HOMOLOGIES OF FRUITS
SOME casual observations of the berries of a Berberis in my
garden directed my attention to the fact that the seeds in the
ripe fruit were harder, smaller, and lighter in weight than
those of the green berry, or, in other words, that seed-contraction
had taken place within the moist fruit. This was established
by further investigation, as shown by the results tabulated
below. The curious circumstance that the seeds of Berberis
had undergone shrinkage in the ripening berry gave me a clue
for attacking the problem concerned with the homologies in
the maturation of different kinds of fruits, especially of the
berry, capsule, and legume. It led me to study the conditions
of seed-shrinkage and of seed-coloration in fruits generally,
and as a matter of course this in its turn led to the investiga-
tion of the dehiscence and drying of the fruits with which such
matters are closely bound up. It kept me clear of the en-
tanglement of the controversy relating to the priority of the
TABLE SHOWING THE CONTRACTION OF THE SEEDS OF BERBERIS
IN THE RIPENING BERRY.
Condition of fruit.
Condition of seeds.
Average weight
of a seed.
Average length
of a seed.
Full-sized green berry just
beginning to colour
Ripe berry
Soft and green
Harder and brown
o'23 grain
0-19 ,,
4*5 millimetres.
3 '5-4 >,
The shrink-
age of seeds
in the moist
berry affords
a clue for the
comparison
of fruits in
their ripen-
ing stages as
illustrated
(a) by Ber-
beris,
The loss in weight of the seed was about 17 per cent.
241
16
242
STUDIES IN SEEDS AND FRUITS
(/>) by Arum
maculatum,
capsule and the berry by finally causing me to regard the
baccate condition as one that may be imposed on a variety of
fruits, not only on the capsule but on the legume, as in the
Tamarind, Acacia Farnesiana, and some species of Cassia, but
also on the nucule, as with some Labiatae.
The indications in this table are sufficiently evident. Sub-
sequently, on investigating this point in the cases of Arum
maculatum, Tamus communis, and Passiflora pectinata, I found
that there also a marked contraction of the seeds occurred
whilst the berry was passing from the green unripe stage into
the red, juicy, mature condition.
In the instance of Arum maculatum, after a comparison of the
full-sized green and red berries on the same spike, and con-
taining the same number of seeds for several plants, the follow-
ing results were obtained.
TABLE SHOWING THE CONTRACTION OP THE SEEDS OF
ARUM MACULATUM IN THE RIPENING BERRY.
Condition of fruit.
Condition of
seeds.
Average weight
of a seed.
Average size
of a seed.
Full-sized green berry .
Red berry . ,
Whitish and un-
wrinkled.
Reddish and
wrinkled.
i "i grain
'9 >,
6 millimetres.
5
The loss in weight of the seed was about 1 8 per cent.
It is thus shown that in spite of their immersion in a moist
pulp, the seeds in the reddening berry of Arum maculatum
underwent a noticeable contraction and loss of weight. To
the eye the contrast is greater than appears in the figures of
the table, since the change is associated with marked differences
in the general appearance and condition of the seeds. On the
one hand, the seeds of the green berry are not only larger and
heavier, but they are distinguished also by their whitish hue
and their unwrinkled surface. On the other hand, the seeds
of the red berry, besides differing in size and weight, are
reddish, wrinkled, and somewhat harder. The embryo in both
CLUE TO THE HOMOLOGIES OF FRUITS 243
cases is rather less than half of the seed's length, the chief
difference being in the albumen, which is rather mealy in the
seeds of the red berry and more fleshy in the seeds of the
green berry. Another indication of the contraction of the
seed in the moist ripening berry is to be found in the decrease
in the relative weight of the coats. Since the coats form 33
per cent, of the weight of the entire seed in the green berry,
and 25 per cent, in the red berry, we see that these seeds
follow the principle laid down for shrinking seeds in
Chapter IX.
The fruits of Tamus communis give us the same indications, (e)byTamus
the seeds of the ripe red berries being smaller, less heavy, and
rather harder than those of the full-sized unripe green berries.
There seemed at first to be an intermediate stage, when the
berries assumed a yellowish hue, but this proved to be con-
nected with the premature withering of the parent stem. In
making such observations it is necessary to compare berries
growing on the same branch. The table subjoined gives
the average of a large number of weighings and measurements,
almost all yielding similar results.
TABLE SHOWING THE CONTRACTION OF THE SEEDS OF
TAMUS COMMUNIS IN THE RIPENING BERRY.
communis.
Condition of fruit.
Condition of seeds.
Average weight
of a seed.
Average size
of a seed.
Full-sized green berry
Red berry
Greenish-yellow
Brown and harder
0-57 grain
o'S 2 ,.
3 '9 millimetres.
3'6
The loss in weight of the seed was about 9 per cent.
The loss of weight (about 9 per cent.) of the shrinking seed
in the ripening berry is not great, and a much greater loss is
sustained when the seed is exposed to the air, as is shown in
the results given a page or two later. The individual differ-
ences in weight and size in the seeds of Tamus communis seem
small, but they become considerable when forty or fifty seeds
are weighed together or measured in a line. The seeds of
(d) by Passi-
flora
pectinata.
244 STUDIES IN SEEDS AND FRUITS
the green berry are greenish yellow, whilst those of the red
are brown, the " browning " beginning in the green berry.
In both stages the seeds are firm and the albumen solid, but
the brown seeds are rather harder.
From the berries of Passiflora pectinata, a species first
described from the Bahamas, the same evidence is obtained.
I made a study of these fruits in the island of Grand Turk at
the southern end of the group. In the red mature berry the
dark purplish crustaceous seeds are enclosed each of them in a
moist, pulpy aril, as is characteristic of the genus, the whole
interior of the fruit being moist. In the green, full-grown
unripe fruit, the seeds are dark green, heavier, larger, and
rather softer than in the ripe berry, the interior of the fruit,
together with the saccate arils, being relatively dry. The results
of my observations may be thus tabulated.
TABLE SHOWING THE CONTRACTION OF THE SEEDS OF
PASSIFLORA PECTINATA IN THE RIPENING BERRY.
The signifi-
cance of the
shrinking of
the seed in
the moist
berry.
Condition of fruit.
Condition of
seeds.
Average weight Average length
of a seed. of a seed.
Average breadth
of a seed.
Full-grown, dryish
green berry
Dark green and
semi-crusta-
ceous in dryish
arils
0-35 grain
5*8 millimetres.
3 "5 millimetres.
Red, ripe, moist
berry
Dark purplish
and crustaceous
in moist, pulpy
arils
Q'3 1
5'3
3'3
The loss in weight of the seed was about 1 1 per cent.
The shrinking of the seed immersed in the moist pulp of
a berry is significant in many ways, and particularly because
it supplies, as already observed, a clue by which we can trace
the homologies in the maturing and drying stages of very
different types of fruits. Or perhaps we would better
describe it as affording a datum-mark to which we can reduce
for purposes of comparison the various conditions presented
by such fruits.
CLUE TO THE HOMOLOGIES OF FRUITS 245
It has first to be noticed that the loss of weight which the
seeds of these berries undergo in the moist fruit is but a small
proportion of the loss which they sustain when subsequently
freed by decay of the berry and exposed to the air. If the
seed of Tamus communis loses 9 per cent, in the reddening
berry, its total loss of weight when dried in free air amounts
to about 46 per cent., as shown in the results tabulated below.
The seeds of Berberis, Passiflora, and of Arum maculatum^ which
give the same indications, are there compared with it. One
can recall familiar instances of the shrinking, hardening, and
" browning " of seeds in fleshy fruits such as the Apple, the
Sapodilla, and the Star Apple ; but here, though the change is
evident to the eye, it is not easy to give a numerical value to
the difference without a carefully guarded comparison of the
average weight of the seeds in a large number of the full-
sized unripe and ripe fruits. As the green apple mellows, its
soft white seeds become smaller, harder, and brown in colour.
The same process is familiar in sapotaceous fruits like the
Sapodilla and the Star Apple (Achras Sapota and Chrysophyllum
Cainito\ where, as the fruit ripens, the soft white seeds become
hard and brown.
In the following table the loss in weight of the seed in the
ripening berry is compared with the total loss when the berry
dries up.
CHANGES IN THE WEIGHT OF SEEDS OF BERRIES DURING THE
RIPENING AND DRYING UP OF THE FRUIT.
Weight of a seed in grains.
Relative weight of a seed,
taking the seed of the
green berry as 100.
Green
berry.
Ripe
berry.
Dried-up
berry.
Green
berry.
Ripe
berry.
Dried-up
berry.
Berberis (species of) .
Arum maculatum
Tamus communis
Passiflora pectinata
0-23
1*10
0-57
'35
0*19
o'go
0-52
0-31
0'12
'5S
0-31
O'2O
IOO
100
IOO
IOO
83
Sz
9 1
89
52
5
54
57
246
STUDIES IN SEEDS AND FRUITS
Comparison
haviour of
thoseofother
fruits.
First,
Hippo-
castamim).
This table supplies a means of comparing the behaviour
during the maturing and drying stages not only of the seeds
^ ^ er kinds of fruits, but of the fruits themselves, and
particularly of the capsule and the leguminous pod.
We will first take the Horse-chestnut (&sculus Hippo-
castanum\ which almost acquires the baccate habit, though its
familiar condition, as it lies open on the ground, is that of a
dryish dehiscent fruit. The same preliminary shrinking of
the seed, associated with hardening and " browning " of the
seed-coverings, takes place in the closed capsule. These
changes, however, only occur in the last stage of maturation
immediately preceding dehiscence. As the green fruit mellows
with maturity it becomes yellowish, and it is during this
,1 , , , - ,
mellowing stage that the shrinking, hardening, and browning
of the soft white seed take place within.
If the soft white seed is removed and allowed to dry in
the air, its coats rapidly harden and assume the characteristic
reddish-brown hue, a change which experiment showed to be
associated with a loss of 17 per cent, of the original weight.
The hardening and coloration of the coverings were completed
in twenty-four hours, when the seed was placed in a warm, dry
cupboard ; whilst in diffuse light in a damp room they occupied
two or three days, an indication that these changes are the result
of partial drying only and do not require the action of light.
If we wished to designate the particular stage in the
maturation of the capsule of the Horse-chestnut correspond-
ing to the ripe berry, we should select the mellowing stage
immediately preceding dehiscence, when the green capsule
assumes a yellowish tinge. It is then, and we are now
indebted to the clue supplied by the seeds of the Herberts berry,
that the seed undergoes its preliminary shrinking and that the
hardening and colouring of its coverings within the closed
capsule occur. Like the seeds of the berry also, it has yet
much more water to lose. It has been already implied that as
soon as the capsule begins to open it displays a well-browned,
hard-coated seed (or seeds), which, as indicated by an experi-
CLUE TO THE HOMOLOGIES OF FRUITS 247
ment before described, has already sustained before dehiscence
a loss of water to the extent of 17 per cent, of its original
weight as a soft white seed. When such seeds after removal
from the naturally dehiscing fruit are allowed to dry in the air
of a room, the total loss of weight finally amounts to about
53 per cent. Thus, to take an example, a soft white seed
freshly removed from a full-sized green capsule and weighing
300 grains would weigh about 250 grains when first exposed
as a brown, hardening seed in the fruit commencing to dehisce.
In the air it would rapidly dry, until it ultimately assumed a
stable weight, subject only to hygroscopic variations, of about
142 grains. Stated as percentages, these changes in weight in
the successive stages of drying would be as follows :
Soft white seed . . . . . . 100
Same seed after some hardening and shrinking in ) R
the closed capsule j 3
Same seed after the drying process has been 1
completed in the open capsule j
Such are the indications supplied by the Horse-chestnut
seeds and by comparing them with the data before given for the
berries of Berberis, Passiflora, Arum maculatum, and Tamus communis,
it will be at once perceived that they run well together with
the indications of the berry. There is the same preliminary
shrinking of the seeds within the closed ripening fruit, and
there is the same great loss of weight when the fruit has passed
maturity and begins to dry. Whether the seed undergoes
the greater part of its drying within a shrivelling berry or
exposed in an open capsule, the process belongs to the same
stage in the history of the fruit. We can now perceive how
the shrinking of the seed in the ripening berry comes to our aid
in contrasting other fruits in their several stages of maturation
by enabling us to fix on a stage that is common to all.
My next example of a capsular fruit will be that of Iris iris Pseud-
Pseudacorus. Here, as in jEsculus Hippocastanum, the Horse- acorus -
chestnut, the soft white seeds of the green full-sized capsule
begin to shrink and harden and commence to " brown," whilst
248 STUDIES IN SEEDS AND FRUITS
the fruit is mellowing and assuming a yellowish hue before
dehiscence. Since the soft white seeds of the green capsule
lose 60 per cent, of their weight when allowed to dry, and since
the brownish seeds in the capsule on the eve of dehiscence lose
about 50 per cent, of their weight when exposed to the air, it
follows that about 20 per cent, of their weight is lost by the
soft unripe seeds when shrinking in the ripening fruit before
dehiscence. We thus get for Iris Pseudacorus results very
similar to those obtained for the Horse-chestnut. Both display
the regime of the berry in the drying of their fruits and
seeds, processes quite independent of any distinction that may
be drawn between baccate and capsular fruits. Here again
the mellowing, greenish-yellow stage immediately preceding
dehiscence corresponds to the ripening of the green berry when
it reddens in Arum, Tamus, etc. I have compared the results
for these two capsular fruits in the table below with the mean
result for a berry as supplied by the data for Herberts, Arum
maculatum, Tamus communis, and Passiflora pectinata.
COMPARISON OF CAPSULES AND BERRIES WITH REGARD TO THE
RELATIVE WEIGHT OF THE SEEDS DURING MATURATION AND
DURING THE DRYING PROCESS, THE WEIGHT OF THE SEED IN THE
FULL-SIZED GREEN OR UNRIPE FRUIT BEING TAKEN AS 100.
Soft white seeds
in the full-sized
green capsule.
Seeds in the ripe
capsule on the
eve of dehiscence.
Seeds dried in
air after being
freed from the
dehisced capsule.
^Esculus Hippocastanum
( Horse-chestnut)
Iris Pseudacorus .
Mean results for a berry (see
table before given)
IOO
100
3
80
47
40
Seeds in the full-
sized green
berry
Seeds in the ripe
berry
Seeds in the
shrivelled and
dried-up berry
IOO
86
S3
The weights of an average Horse-chestnut seed in the three stages are 300, 250, 142
grains ; and for Iris Pseudacorus, 2*0, i'6, and o'8 grain.
CLUE TO THE HOMOLOGIES OF FRUITS 249
Observations of this kind extend over a year or two and
require a little patience, since the same locality has often to be
visited several times, and much also has to be done at home.
I will now take a fruit intermediate between a capsule and Second,
a berry, the baccate capsule of Thespesia populnea, a tropical capsules
beach tree of the malvaceous order. The full-sized yellowish-
green fruit possesses an abundant, thick yellow juice and white, populnea.
softish seeds. In the next stage it becomes a darker green,
the juice becomes scanty, and the seeds shrink a little, harden,
and assume a purplish tinge. Then the fruit begins to
" brown " rapidly, and its sides collapse ; whilst its seeds also
turn brown, and, continuing to dry and harden, ultimately lose
about half their original weight when the drying of the fruit
is complete. Finally, the fruit breaks down and the seeds are
freed by its decay. In the figures 100, 87, and 50, which
represent the relative weights of the white softish seed, of
the purplish seed before drying of the fruit has actively
commenced, and of the brown, hard seed in the fruit when the
drying has ended, we have stated numerically the essential
stages of the capsule and the berry. The actual weights of an
average seed in these three stages would be 5-5, 4' 8, and 2*25
grains. An index of the changes in the fruit is afforded by the
changes in the condition of the adherent calyx, which remains
moist and green long after the seeds within have begun to shrink
and harden, and only begins to wither when the capsule com-
mences to " brown " and to lose weight, thus indicating that the
first shrinkage of the seed within the still moist fruit, as in the
case of the true berry, precedes the active drying of the capsule.
With the ordinary dehiscent leguminous pod there is Third,
quite another regime. In illustration I will first take that
of Ctesalpinia sepiaria, the familiar " Wait-a-bit " of Jamaica. Caesalpinia
The full-sized green pod with its white, soft seeds represents
the green capsules of the Horse-chestnut and Iris Pseudacorus
and the green berries of Herberts, Arum maculatum, and Tamus
communis after they have attained their maximum size. In the
next stage, which corresponds to the ripe berry and the mellow-
2 50 STUDIES IN SEEDS AND FRUITS
ing capsule before dehiscence, the pod turns yellowish green and
the white seeds experience the preliminary shrinkage and
hardening and take on a greenish hue. Then active drying of
the pod and seeds commences ; but before dehiscence begins
the shrinking and hardening of the seeds have been almost
completed, so that in the opening pod we find normal dark,
mottled resting seeds that will perhaps lose another 10 per
cent, of the original weight in keeping. The respective
weights of the seeds in the green pod, in the pod turning
yellowish, and in the dried pod on the eve of dehiscing, are
8-3, 6*2, and 3*8 grains, which stand to each other as 100, 75,
and 46, and thus indicate the three stages of the berry.
Some of the processes involved in the general shrinking of
leguminous pods and seeds will be discussed more in detail
in the succeeding chapter. Here I will only refer to cases
which seem specially suggestive for determining the stages in
maturation and in the drying process that are homologous or
are truly comparable with those in the capsule and berry. In
Ulex euro- this connection the pods of Ulex europteus occupied much of
paeus(Gorse). my attent i on> They were the first fruits to which I applied
the clue afforded by the Berberis berry. Though much of
their behaviour is characteristic of the typical leguminous pod,
it is not always that we find the stages so well defined.
With Ulex europteus practically all the shrinkage, hardening,
and coloration of the seeds are carried out in the closed pod ;
and when the pod dehisces it exposes to view the normally
contracted hard seeds. Three stages in the maturation and
drying of the fruit are distinguished by the colour of the seeds.
When the green pod has reached its full size they are soft
and bright green, a hue that they owe mainly to the dark
green embryo which can be seen through the thin coats. Then
follows a stage which corresponds seemingly to the first failure
of the nutrient supplies from the mother plant. The soft green
seeds turn a greenish yellow as the pod begins to dry and darken.
But there is no very evident shrinking of the seed, though the
cord withers. That is only detected by careful measurement and
by the balance, since it is slight in amount. The colour-change
again is largely due to the change in colour of the embryo.
The last stage is occupied with the active drying of the darken-
ing pod, the yellow seeds contracting and hardening rapidly and
adopting the permanent chocolate-brown colour of the normal
resting seed. In this stage, however, the change in seed-colour
is mainly an affair of the coverings, whilst in the two earlier stages,
marked by green and yellow seeds, it was largely concerned
with the embryo. This last stage closes with the completion
of the drying of the pod in the sun's rays, and the pod dehisces
suddenly, giving rise to those curious little clicks that one hears
so frequently when standing near a gorse bush on a sunny day.
Now all these changes in the seeds of Ulex europ<eus, from
the soft green state to the hard chocolate-brown condition,
are carried on in the closed pod. In fact, all three stages
may be observed together in the same pod. The discolora-
tion begins at its distal end, and before the blackening process
has extended down one-third of the pod's length all the seeds
will have changed their hue from green to yellow. When
it has affected four-fifths of the pod, the uppermost seeds
will be found actively shrinking, hardening, and colouring
chocolate brown ; and by the time the whole pod has blackened
all the seeds will be in that condition. But although the
pod has dried considerably during the blackening process, it
is still fairly moist at its completion ; and the seeds, though
considerably reduced in size and no longer soft, are far from
being as hard as in the normal resting seed, and have yet to
decrease in size. Up to this point there has been no opening
of the pod, and the completion of the drying process and the
ultimate dehiscence are soon affected by exposure to the sun.
It has been noted above that the green and yellow seeds
have green and yellow embryos, the colouring of the soft
seeds depending in these two stages mainly on the colour
of the embryos. This change from green to yellow is
probably connected with the failing of the nutrient supplies,
since it coincides with the commencement of the withering
The corre-
spondence
between a
legume and
a berry.
252 STUDIES IN SEEDS AND FRUITS
of the cord or funicle. But the change in the last stage
from yellow to chocolate brown is exclusively associated with
the drying process. This is indicated by a simple experiment.
If a yellow seed is allowed to sink in a glass of water no altera-
tion takes place. But if it is allowed to rest on the surface for
a day or two, the lower submerged portion preserves its yellow
hue, whilst the upper part exposed to the air turns brown.
TABLE SHOWING THE SHRINKAGE OR CONTRACTION OF THE SEEDS
OF ULEX EUROP^EUS (GORSE) IN THE POD BEFORE DEHISCENCE.
Condition of pod.
Condition of
seeds.
Weight of a seed.
Size of a seed.
Green and full-sized
Beginning to discolour and
to dry
Dried and on the eve of
dehiscing
Soft and green.
Soft and greenish
yellow
Hard and choco-
late brown
o'zs grain
O'ZO
O'll ,,
4-4*5 millimetres.
3-3'S
2'5
The loss in weight in passing from the green to the yellow stage is 20 per cent. ;
whilst the total loss experienced is 56 per cent.
If we wished to determine the correspondence in the
maturing and drying stages between a leguminous pod like
that of Ulex euro-pans and a berry like that of Berberis, we
would do so in this fashion :
| Green pod, with soft green seeds of Ulex.
' \ Green berry, with soft green seeds of Berberis.
r Green pod of Ulex commencing to darken, with green seeds
\ turning yellow and shrinking slightly.
" i Colouring berry of Berberis^ with seeds turning brown and
v becoming smaller and harder.
r Pod of Ulex rapidly drying and blackening, with seeds turn-
\ ing brown, shrinking greatly, and hardening.
*" I Berry of Berberis rapidly shrivelling, with seeds losing much
N- water and hardening.
f Dried pod of Ulex liberating its seeds by dehiscence.
4. J Shrivelled berry of Berberis liberating its seeds through the
( decay of its coverings.
The correspondence in the fourth stage will perhaps be least
expected. But when one reflects that the opening of a pod,
CLUE TO THE HOMOLOGIES OF FRUITS 253
however methodical the process may appear to be, depends
on a structural character which was originally developed for
a special purpose in the living plant and could have had no
concern with the liberation of seeds from a dead pod, we
must confess that this appearance of method is purely accidental.
It is an accident that I am able to avail myself of the binder's
crease in tearing the sheets of a book into regular portions ;
and to that extent the mode of dehiscence is accidental with
the Ulex pod. It will subsequently be shown that if this
parallelism between the dry, dehiscing pod and the decaying,
shrivelled berry is valid, it ought to have a far-reaching
influence on our views of adaptation and seed-dispersal.
My readers will in this connection recall those numerous
leguminous pods that liberate the seeds only by breaking
down through decay, and 1 shall in a later page point out
that the peculiar form of moniliform pods, which is there
described, is probably determined by constrictions induced in
an earlier stage of the development of the fruit by the abortion
of the ovules, and the premature shrinking of the seeds.
COMPARISON OF THE MEAN RESULTS OBTAINED FOR BERRIES, CAPSULES,
AND LEGUMES, WITH RESPECT TO THE RELATIVE WEIGHTS OF THE
SEEDS DURING THE MATURATION AND DRYING OF THE FRUITS, THE
WEIGHT OF THE SEED IN THE GREEN UNRIPE FRUIT BEING TAKEN
AS 100.
In the green berry
In the ripe berry
86
In the dried-up, shrivelled
berry
53
In the green capsule
In the green legume
In the ripe capsule on the
eve of dehiscence
8a
In the green legume turn-
ing yellow or beginning
to blacken
78
When dried in air after the
opening of the capsule
44
In the dried-up legume on
the point of dehiscing
45
The results here given are for the berries of Berberis, Passiflora, Arum maculatum,
and Tamus communis ; for the capsules of ^Esculus Hippocastanum (Horse-chestnut) and
Iris Pseudacorttt ; and for the legumes of Ccesalpinia sepiaria and Ulex europaus (Gorse).
254 STUDIES IN SEEDS AND FRUITS
Thecorre- We see from these results that in the ripe berry only a
between" small shrinkage of the seeds occurs, namely, about 14 per cent.,
berries, anc j t } iat t h e seec [ s have still much of their water to lose in
capsules, and
legumes. drying. In the capsule the same small shrinkage takes place
before dehiscence, but the principal loss of weight and the
greater part of the contraction occur after the seeds have
been exposed to the air. In the pod practically all the shrink-
age of the seeds is carried out in the closed fruit, and when
dehiscence occurs normal resting seeds are exposed. The
seeds of a capsule are thus placed at a disadvantage when
compared with those of a pod, since in the pod the seeds
are protected until sufficiently hardened, whilst in the capsule
they are usually exposed in a relatively soft and in a less
protected state on account of the dehiscence taking place at
a much earlier stage.
The parallelism, or rather the correspondence, between
the stages of the maturation and the drying of berries,
legumes, and capsules, may be put in the following manner :
(1) The green berry, the green capsule, and the green
legume of maximum size, with their large, soft, white or green
seeds, are all in the same stage.
(2) The ripe, juicy berry, the mellowing, still closed capsule,
and the legume- just beginning to discolour represent the
next stage, which is characterised by a slight shrinking of
the seeds, and by their coloration when white, or by a
change of colour if green. Though evident enough in the
berry, this stage is transient and often disguised in the capsule
and legume, points which will be further discussed in the
succeeding chapter. It is early in this stage that the shrinking
of the cord or funicle marks in dehiscent fruits the commence-
ment of the severing of the seed's connection with the parent
plant.
(3) The shrivelling berry, the capsule dehiscing and losing
much of its water in the air, the drying and blackening but
still closed legume, belong to the next stage. Dehiscence
occurs at a much earlier stage with the capsule than with the
CLUE TO THE HOMOLOGIES OF FRUITS 255
legume. As shown in Chapter XIII, the legumes lose before
dehiscing nearly all the water they can yield to the air ; whilst
the capsule before it opens may not even have commenced
to dry, or loses only a small proportion of the water that it
ultimately gives up in the air-drying process. The greater
part of the shrinking and of the hardening of the seeds belongs
to this stage.
(4) This stage characterises only the berry and the legume,
since the dried capsule has already completed its stages and
is lying widely open with its seeds falling out. The shrivelled
berry and the dry pod now in their turn liberate their seeds,
the one by decay and the other by dehiscence.
Such are some of the principal points brought out in
this comparison of the capsule, legume, and berry. Additional
evidence will be adduced in support of most of them in
the following chapters.
There is much that is significant in this correspondence
between these three different kinds of fruits, and much that
we should bear in mind when we speak of special adaptation The question
for dispersal of fruits and seeds. Though there is a great ion. aP
deal that may please the eye and captivate the fancy in the
mechanisms of a dehiscing pod or capsule, it is doubtful
whether they represent anything more in nature than the
rotting apple and the shrivelling currant. The exposure
of the brightly coloured seed in the opening pod, as in
Abrus, Adenanthera^ and Erythrina, often adds beauty to the
plant ; yet, viewed from this standpoint, it is nothing more
than one observes in the seeds exposed in the decaying
orange and in the rotting Anona fruit as they lie on the
ground. If the seeds in the ripe berry, or mature baccate
fruit, are in the same stage as those in the mellowing capsule
before it opens, or in the closed, full-sized green legume on
the eve of drying, then the shrivelled berry represents the
dried- up open capsule and the shrunken but still closed
legume.
In all three fruits the shrivelling and drying, whether
256 STUDIES IN SEEDS AND FRUITS
accompanied or not by dehiscence, seem to betoken a stage
that was not, if I may use the expression, in the original
plan laid down for nature. The biological connection being
severed with the parent plant, the fruit dies, but the seed lives.
There was a time, as I hold, in the age of vivipary, when
uniform climatic conditions prevailed, and the embryo was
already well advanced in germination and able to start life for
itself before the severance from the parent took place. In
later ages climatic differentiation has intervened, and the fruit
dies, leaving the embryo in all stages of arrested growth, with
the chances of its future development by no means assured.
The embryo is then dependent for its protection on the
hardening of its coverings, a process mainly accomplished after
the cord has withered, and in a fruit no longer drawing its
nutrient supplies from the parent, but practically dead.
It is hard to detect anything but a baffled design when we
see nature suddenly withdrawing the plant's fostering care
over its offspring and leaving all to chance. It is difficult to
perceive any evidence of adaptation for dispersal in a rotting
apple ; but if my view is correct, the same should be true of
dehiscent fruits, the withering and opening of which, though
seemingly displaying more of method, are equally determined
by external influences of a haphazard kind.
SUMMARY
(1) The shrinkage of seeds in the moist berry affords a clue for
the comparison of fruits in their ripening stages, as illustrated by
Berberis (p. 241), Arum maculatum (p. 242), Tamus communis (p. 243),
and Passiflora (p. 244). Thus guided, we can trace the homologies in
the maturing and drying stages of very different types of fruits. This
shrinkage within the moist berry, which involves a loss of weight on
the average of from 10 to 15 per cent., represents but a small proportion
of the total loss which the seed sustains when exposed to the air or
dried with the fruit.
(2) It is the shrinking of the seeds in the ripening berry that
comes to our aid in contrasting other fruits in their several stages of
maturation by enabling us to fix on a stage that is common to all.
CLUE TO THE HOMOLOGIES OF FRUITS 257
Thus in the case of capsular fruits, like those of the Horse-chestnut
(/Esculus Hippocastanum] and of Iris Pseudacorus^ we see displayed the
regime of the berry in the preliminary shrinking of the seeds within
the ripening fruit and in the subsequent great loss of weight when the
fruit has passed its maturity and dries in the air. Here, then, it
becomes evident that the green berry and the green capsule are in the
same stage, the ripe juicy. berry and the mellowing still closed capsule
in another stage, and the shrivelling berry with the drying, dehiscing
capsule in a third stage.
(3) With the ordinary dehiscent leguminous pod, as illustrated by
the behaviour of those of Cessalpinia sepiaria and Ulex europteus^ there
is quite another regime, since dehiscence occurs much later than in the
capsule ; but here also the preliminary shrinking of the seeds and other
changes in the fruit enable us to detect the equivalents of the stages
of the berry and the capsule in those of the leguminous pod. We
thus learn that the berry, the capsule, and the legume, in the full-
grown green or so-called unripe condition with large soft seeds, are
in the same stage. The ripe, juicy berry, the mellowing, still closed
capsule, and the green legume just commencing to discolour represent
the next stage in the maturation of the fruit, which is characterised
by a slight shrinking and hardening of the seeds. Then the berry
shrivels, the capsule dehisces and dries, and the legume darkens
and dries rapidly, but still remains unopened, the shrinking and
hardening of the seeds being in all cases actively continued. When
the last stage arrives the dry capsule has already completed its history
and lies gaping widely, with its seeds falling out, whilst the shrivelled
berry and the dry legume now liberate their seeds, the first by decay,
the second by dehiscence.
(4) If the seeds in the ripe berry are in the same stage as those
of the mellowing capsule before dehiscence and of the full-sized moist
legume on the eve of drying, then the shrivelled berry represents the
dried-up open capsule and the dry legume or pod on the point of
dehiscing. From this standpoint, therefore, the mechanism of a
dehiscing legume or capsule, however adaptive its appearance, does not
count for anything more in nature than the rotting apple or the
shrivelling currant. If we are not able to detect any signs of adapta-
tion for dispersal in a decaying berry, the same should be true of
dehiscent fruits, the withering and opening of which, though
apparently displaying more of method, are equally determined by
external influences of a haphazard kind.
CHAPTER XII
THE HOMOLOGIES OF FRUITS AS REVEALED IN THE
DRYING PROCESS
THIS chapter is concerned principally with the story of the
drying fruit, or rather with the indications that it supplies.
Here again it is to the balance that we look for our data, and
it will be seen that the results obtained are of some interest
and often unexpected in their significance. Without further
introductory remarks I will at once plunge into the middle of
my subject.
Indications It is very suggestive that two such different-looking fruits
trastbetween as those of Barringtonia speciosa and Ribes Grossularia (Goose-
the berries of berry), both of which are characterised by the systematic
Barringtoma ' ** . . ' 11
speciosa and botanist as berries, give off when allowed to dry naturally in
Grossularia the air the same amount of water, losing in each case about
^5 P er cent ' ^ ^ Gir we ^g nt m the ripe condition. The one, a
large fruit 8000 to 9000 grains in weight, is described as
corticate and fibrous, whilst the other, weighing about 100
grains, is described as succulent and pulpy. Even if the air-
dried fruits of both plants were subsequently exposed in the
oven to a temperature of 100 C., the relative weight of the
water-free residues would not differ greatly in amount, that of
the Gooseberry being probably about 10 per cent., and that of
Barringtonia speciosa about 13 or 14 per cent, of the moist
fruit. For details of the experiments on the Gooseberry see
Note 10 of the Appendix.
When comparing two such different-looking kinds of
258
THE HOMOLOGIES OF FRUITS 259
berries we are likely to begin with a misconception. The dry, Misconcep-
husky, symmetrical fruit of Earringtonia speciosa, such as the
currents disperse over the coral islands of the Pacific, is a dried
berry, and as such is only to be compared with the shrivelled are not in the
< r i ^ i TII i i r i -r i same stage.
fruit of the Gooseberry. This lack or adjustment is frequently
met with in comparing the stages of fruits. Take, for
instance, the distinction which the systematist usually draws
between a berry, as fleshy and indehiscent, and a capsule, as
dry and dehiscent. Here we are contrasting the air-dried
capsule with the moist berry, two quite different stages in the
history of these fruits. Naturally, the true correlative of the
dry dehiscent capsule would be the shrivelled berry, whilst the
ripe berry would find its homologue in the full-grown moist
capsule as we find it living on the plant. This relation
between the berry and the capsule has been already dealt with
in Chapter XI. The necessities of the systematist are partly
responsible for the incongruities in the comparison of fruits,
since he gives a place to the dry fruit that retains its shape,
but refuses to recognise as on the same footing the dried-up
berry or the shrivelled drupe. But part of the blame must
lie with one's natural repugnance to the shrivelling process,
seemingly so significant of inutility and death. Let but the
form be preserved, even though the life of the fruit has gone,
and we become apt to attach importance to a distinction which
is purely accidental and in no sense ordinal in character.
These remarks do not at all exaggerate the lack of true
adjustment which prevails in the general classifications of
fruits. It is far from easy to see how this can be avoided in
practical systematic botany, but the inconsistency remains.
There lies beside me The Handbook of the British Flora , by
Bentham and Hooker (5th edit., 1887), and there I read
(p. 36) that fruits are generally divided into "succulent" and Thedistinc-
" dry," the first being usually indehiscent, whilst the second
are often dehiscent and open at maturity. The succulent systematist
fruits are there typified by the berry and the drupe, and succulent
the dry fruits by the capsule, legume, achene, etc. Of
260 STUDIES IN SEEDS AND FRUITS
the dehiscent capsule and legume it is stated that when ripe
the pericarp usually splits into valves. One may note in
passing that this can only be said of the capsule. How-
ever, each of these statements taken independently has the
sanction of experience ; but it is an error to connect them
together in a classification of fruits, since they are essentially
incongruous.
In the first place, as regards the two main divisions into
succulent and dry fruits, it is apparent that we are here con-
trasting moist fruits that have yet to dry with those that have
more or less completed the drying process. As already
indicated in Chapter XI, the moist fruit is a living fruit,
whilst the dry fruit is a dead one. Strictly speaking,
there is no such marked distinction in nature between moist
Nature does and dry fruits, except such as is connected with the differ-
sucha - 8 ^ 6 ence between a living and a dying or dead fruit. To be
distinction, convinced on this point we have only to look at the
columns of the following tables, though this view has
already been established in the previous chapter. Where,
for instance, are we to find amongst other types of fruits
the stage that is representative of the air-dried capsule of
Datura ? If we followed the method of the systematist
we should find it in the moist drupe of the Sloe (Prunus
communis). A glance at the tables will show that in so doing
we should be comparing a dead and dry fruit with a moist
and living one. Both the living capsule and the living drupe
in these two plants lose about the same amount of water
when they die and dry up (70 to 73 per cent, of their
weight) ; and if we contrast them we should either compare
them when they have attained their maximum size on the
plant as moist living fruits, or when they have lost their
vitality and have dried up. This is the only valid mode of
comparing fruits, and the failure to adopt it leads to erroneous
conceptions of the biological significance of the process of
dehiscence. The dried dehiscing capsule and the shrivelled
drupe go together.
THE HOMOLOG1ES OF FRUITS 261
The same rule applies when we look for the representative
of the Datura capsule amongst the legumes or the berries.
A Canavalia pod, an Arum berry, and a Datura capsule
contain about the same amount of water in the full-grown
living state, and can only be compared in the same condition
either as moist living fruits or as dry dead ones. We thus
come to perceive that all fruits, when they reach maturity
on the plant, whether drupes, legumes, berries, capsules, All mature
etc., are moist fruits and cannot be distinguished from each are'moist 1 S
other by their water-contents. Nature does not recognise frmts>
the distinction between moist drupes and berries on the
one hand and dry legumes and capsules on the other.
Group for group, the contrast between capsules, legumes,
berries, drupes, etc., as regards their water-contents in the
full-grown living condition, is relatively small ; and in
each group we find much the same variation in the amount
of water lost in drying, namely, between 50 and 80 or 85
per cent.
The differences are mainly developed when we allow the
drying to take place in all cases, the berry and the drupe to
shrivel up, and the capsule and the legume to dry and dehisce,
the ultimate contrast between the asymmetry of the one kind
and the retention of the regular form in the other being
dependent on the nature of the tissues composing the pericarp.
Nature makes no deliberate effort to assist the systematist,
and inconsistencies of the kind above noted are inseparable
from our necessarily arbitrary endeavours to systematise her
processes. The error involved above is of course the com-
parison of fruits that are not in the same stage. But other
inconsistencies are apt to follow. Thus, as already noticed, it
is implied in the above statements from The Handbook of the
British Flora, that dry dehiscent fruits like those of the capsule
and the pod open when they are " ripe." This might indicate
that dehiscence occurs in these fruits in the moist, mature
condition. But, as we will see in Chapter XIII, this is
only true of the capsule, the legume opening when the fruit
STUDIES IN SEEDS AND FRUITS
ry and dead. The typical capsule which opens before
drying begins, or in the early stage of drying, is just as
much entitled to the designation of " moist " as a berry.
I venture, therefore, to think that these remarks indicate
the necessity of renovating our prime conceptions of the
differences between fruits.
THE Loss OF WEIGHT OF MATURE FRUITS, INCLUDING THEIR SEEDS,
WHEN DRIED IN AIR UNDER ORDINARY CONDITIONS OF TEMPERA-
TURE. (The full-grown moist fruits before drying or shrinking begins
are here employed.)
I. LEGUMES.
Loss of weight after drying in air for
weeks or months.
Number
of seeds.
Char-
acter of
dry
Stated in grains.
Stated as a
percentage.
Stated as
fruit.
water-loss
or water-
Moist
Dry
Moist
Dry
percentage.
weight.
weight.
weight.
weight.
Pisum sativum (Pea)
7
250
So
IOO
20
80
Guilandina bondu-
2
400
95
IOO
24
76
cella
Phaseolus multi-
4
300
75
IOO
2 5
75
florus (Scarlet-
runner
Faba vulgaris
5
75
195
IOO
26
74
(Broad Bean)
Mucuna urens
3
IOOO
280
IOO
28
7*
Canavalia obtusi-
6
400
112
IOO
28
72
folia
Leucsena glauca .
24
IOO
3
IOO
30
70
Entada polystachya
H
800
240
IOO
30
70
Csesalpinia sepiaria
5
IOO
3*
IOO
3 2
68
Cassia fistula
95
Woody
5000
1650
IOO
33
67
Vicia sativa .
10
15
5'6
IOO
37
63
Ca janus indicus
4
40
16
IOO
40
60
Acacia Farnesiana
20
...
150
60
IOO
40
60
Andira inermis
i
Woody
1 3S
54
IOO
40
60
Dioclea reflexa
4
Woody
1800
738
IOO
4i
59
Vicia sepium
3 or 4
6
2-5
IOO
42
5
Ulex europaeus
4 or 5
'S
1*1
IOO
44
56
Poinciana regia
40
Woody
3500
1575
IOO
45
55
Csesalpinia Sappan
4
Woody
260
130
IOO
5
5
THE HOMOLOGIES OF FRUITS
II. CAPSULES.
Loss of weight after drying in air
for weeks or months.
Char
wBBtt*
acter
of
dry
Stated in grains.
Stated as a
percentage.
Stated as
fruit.
water-loss
or water-
Moist
Dry
Moist
Dry
percentage.
weight.
weight.
weight.
weight.
Momordica Charantia
500
75
IOO
15
85
Blighia sapida (Akee)
...
1730
346
IOO
20
80
Scilla nutans .
10
2-4
IOO
24
76
^Esculus Hippocastanum
i seeded
700
168
IOO
24
76
(Horse-chestnut)
Iris foetidissima
170
42-5
IOO
*5
75
Ipomoea tuba .
IOO
*5
IOO
25
75
Iris Pseudacorus
250
65
IOO
26
74
Gossypium barbadense
IOO
26
IOO
26
74
Primula veris (Primrose) .
4
I '2
IOO
3
70
Datura Stramonium .
360
108
IOO
3
70
Allium ursinum
3 seeded
2-4
o'8
IOO
33
67
Thespesia populnea , .
Inde-
230
76
IOO
33
67
hiscent
Swietenia Mahogani (Ma-
Woody
5800
2030
IOO
35
65
hogany)
Hura crepitans .
Woody
3200
1152
IOO
36
64
Hypericum Androssemum
Inde-
3
i 'i
IOO
37
63
hiscent
Viola tricolor .
3
I '2
IOO
40
60
Bignonia (near sequinoc-
Siliqui-
1250
500
IOO
40
60
tialis)
form
Arenaria peploides .
8
3'3
IOO
4*
59
Ra venal a madagascari-
Woody
700
294
IOO
42
5
ensis
Aquilegia (species of)
Folli-
10
4'S
IOO
45
55
cular
Canna indica .
IOO
47
IOO
47
53
264 STUDIES IN SEEDS AND FRUITS
III. BERRIES, DRUPES, etc.
Loss of weight when dried in air
for weeks or months.
Family.
Fruit.
Stated in grains.
Stated as a
percentage.
Stated as
water-
loss or
water-
Moist
Dry
Moist
Dry
percent-
weight.
weight.
weight.
weight.
age.
Pyrus Malus (Apple)
Rosacese
Berry
900
126
IOO
H
86
Ribes Grossularia
Ribesiacese
91
120
18
IOO
15
85
(Gooseberry)
Tamus communis
Dioscoreae
II
H
*'5
IOO
it
82
Opuntia Tuna
Cactese
}
800
144
IOO
18
82
(Prickly Pear)
Citrus aurantium
Aurantiacese
M
2400
460
IOO
'9
Ii
(Orange)
Sambucus nigra
Caprifoli-
II
3*3
07
IOO
21
79
(Elder)
acese
Lonicera Pericly-
Caprifoli-
M
4'8
I '2
IOO
*5
75
menum (Honey-
acese
suckle)
Monstera pertusa
Aracese
II
5'
I 'O
IOO
20
80
Arum maculatum
M
M
6-1
1-8
IOO
2 9
7i
Hedera Helix (Ivy) .
Araliacese
II
5
2
IOO
40
60
Quercus Robur (Oak)
Amentaceae
Nut
60
24-0
IOO
4
60
Prunus communis
Rosaceae
Drupe
30
8
IOO
27
73
(Sloe)
Sparganium ramosum
Pandaneae
ii
i
0-45
IOO
45
55
Barringtonia speciosa
Myrtaceae
Berry
9000
1350
IOO
15
5
Areca Catechu .
Palmaceae
ii
250
80
IOO
3 Z
68
Cocosnucifera (Coco-
i>
Drupe
60,000
18,000
IOO
3
70
nut)
Acrocomia lasiospatha
ii
55
200
IOO
36
64
Arenga saccharifera
Berry
600
300
IOO
5
5
Mauritia setigera
i>
IOOO
560
IOO
56
44
Cocos plumosa .
Drupe
IOO
63
IOO
63
37
Oreodoxa regia
Berry
IS
IO'O
IOO
66
34
Hyophorbe Vers
>i
'5'5
6'2
IOO
40
60
chafftii
Note, The total amount of water in these fruits can readily be ascertained by applying
a small correction to the loss sustained when dried in air. As a rule the air-dried fruits
would lose between 10 and 15 per cent, of their weight when exposed to a temperature
of 100 C. The corrected result for the air-dried berry of Tamus communis ; assuming
that it lost 12 per cent, of its weight in the oven, would be as follows :
Moist weight .... 100
Air-dried weight . . .18
Oven-dried weight . . .16
Loss when air-dried ... 82
Loss when oven-dried . . 84
THE HOMOLOGIES OF FRUITS 265
The contents of the foregoing tables raise a number of
interesting points, and it would be easy to devote some
chapters to the details of the experiments, if space allowed and
necessity required it. Indeed, not a few of these points will
come under our notice when we discuss the relation of parts
in the living or moist and in the dead or dried fruit. There
are, however, some matters that call for immediate notice. It
has already been explained in a note to the tables that a small
minus-correction applied to the air-dried weight will give
approximately the total water-contents, such as would be
indicated by the loss of weight of the fresh fruit when
exposed to a temperature of 100 C. The water remaining
after drying in air is the water of hygroscopicity, which fruits
possess in common with all other vegetable substances, whether
living or dead (see Chapter VII).
Another point here claims attention. It is remarkable how The large
much water fruits described as woody in the dry state contain ^te^in
in the full-grown living condition on the plant. Amongst the llvin f>
fruits that in the dried state specially merit the designation of
" woody," one would certainly include the long pod of Cassia
fistula, the large capsule of the Mahogany tree (Swietenia
Mahogani), and the polycoccous capsule of Hura crepitans (the
Sandbox-tree). Yet each of these fruits, as will be seen in my
tables, loses about two-thirds of its weight when allowed to
dry in free air in the moist, green, full-grown condition,
the water-loss, denoted by the decrease in weight, being
respectively 67, 65, and 64 per cent, of the original weight.
Although the woody fruits lose less water when dried in air
than fleshy fruits, a glance at the tables will show that the
difference is usually not great. If fleshy fruits may lose
between 70 and 80 per cent, of their weight, woody fruits may
lose between 60 and 70 per cent.
But many disturbing influences come into play and prohibit Disturbing
any precise general statement until their effect is determined. ^ e "ting S the
This is at once made evident when we perceive that the woody drying in air
fruits of Cassia, Swietenia, and Hura lose about as much
266 STUDIES IN SEEDS AND FRUITS
water when dried as does the Acorn (Quercus), the capsule of
Viola, and the pods of Vicia and Cajanus. Then, again, it is
apparent that several very different causes have combined to
produce the same result in the Coco-nut, the Acorn, and the
pod of Cassia fistula, all of which lose a similar amount of
water, namely, from 60 to 70 per cent, of their weight. Some
of these causes will be considered when we come to deal with
the relation of parts in a fruit.
The effect of The development of sugars in the ripening berry makes a
material difference in the weight of the fruit after it has been
dried in air. Elder berries (Sambucus nigrd], before the sugars
are formed, lose about 87 per cent, of their weight, but with
the production of sugar their weight during drying is
diminished by only 78 or 79 per cent., the saccharine materials
being especially hygroscopic and preventing the complete
drying of the fruit. The berries of the Honeysuckle (Lonicera
Periclymenum), which, when the sugars are formed, lose about
75 per cent, of their weight, behave in a similar fashion. In
the same way the ripe fruits of the Gooseberry (Ribes
Grossularia] cannot be dried properly in air on account of the
abundance of the sugars. The congealed juice that encrusts
the surface of the air-dried berry is very hygroscopic. The
ripe fruit loses about 85 per cent, of its weight ; but if the
sugars are removed by washing, the air-dried materials make
up only about 5 per cent, of the weight of the moist berry
(see Note IOA of Appendix). The same behaviour is displayed
by the berries of Opuntia Tuna (Prickly Pear), which, when air-
dried, lose 82 per cent, of their weight, but if the sugars are
removed by washing, the dry residue of 1 8 per cent, is reduced
to 12 per cent, (see Note IOB of the Appendix).
The seeds of such sugary fruits often remain moist and
sticky and require washing for their complete drying. Those
of the Pomegranate (Punica Granatum), for instance, never dry
properly unless previously washed. A good example of the
influence of the sugars on the air-drying of fruits is afforded
by the different behaviours of the husky coverings of the ripe
THE HOMOLOGIES OF FRUITS 267
drupes of the Coco-nut (Cocos nuciferd] and of Cocos plumosa.
In the first case there is a loss of quite 80 per cent. In the
second case, where the coverings contain a good deal of sugar,
the loss is only about 55 per cent.
As with the sugars of berries, the presence of oil in the The effect of
pericarp of fruits greatly retards the air-drying process. This
explains why, in my experiments, the drupaceous berries of
Oreodoxa regia (Palmaceae) lost only 22 per cent, of their weight.
In the same way, fragments of the pericarp of the Cashew-
nut (Anacardium occidentale\ which contain a caustic oil in
abundance, dry but slightly, losing less than 15 per cent, of
their weight when exposed to the air.
In connection with the loss of weight sustained by fruits Immature
when dried in air, some curious considerations arise from the more water
fact illustrated in the table below, that immature fruits contain
more water than mature fruits. Although the data there
given refer almost exclusively to immature fruits ot nearly the
maximum size that are characterised by incompletely developed
seeds, they illustrate a process of change that runs through
nearly the whole of the fruit's life-history, from the time of its
occurrence as a young fruit, until, with maturity passed, the
fruit dries up and loses its vitality. But in this respect,
namely, in the progressive decrease of the water-contents as
they pass from youth to maturity, and thence to the loss of
vitality, fruits share the fate of all vegetable substances.
If we regard only the percentage of water in the whole or in this re-
in the part of a plant, whether stem, leaf, root, fruit, or seed, u?u s trate^i
we can construct a scale beginning with the young growth, principle
containing, we will say 70 or 80 per cent, of water, and ending teristic of the
with the air-dried dead substance that holds only the water world.
of hygroscopicity, amounting only to 12 or 15 per cent., the
water which it derives from the air and which it gives up in
the oven. Between the initial and terminal stages of this scale
there is an ever-progressive decrease in the proportion of
water that the living plant-substance yields up when drying to
the air. But this progressive decrease in the proportion of the
268 STUDIES IN SEEDS AND FRUITS
water-contents differs in character in the earlier and later parts
of the period covered by the scale. In the first portion, where
we are concerned with the living plant or its part, the decrease
in the percentage of water is merely due to the fact that during
the building-up processes involved in growth the solids increase
more rapidly than the liquid constituents. In the second
portion, when the plant or its part is dying and drying, there
is an actual loss of water, and this goes on until the plant-
substance, like all other dead vegetable materials, ceases to
give up water to the air and retains only the water of hygro-
scopicity.
Such is the r61e played by water in the life of a plant,
either entire or in part, as stated in terms of the decrease
in the proportion of the water-contents. In active life this
decrease, as just observed, is only relative, and is due to the
more rapid increase of the solids. When the plant dies it is
absolute, and involves the loss of all the water required for
the processes of vitality. But between the period appropriated
by the living plant or its part and the period associated with
death and desiccation, there often seems to be an interval of
varying length characterised by repose. This is the rest-period
that appears to be claimed by all vegetable life, by the plant in
its entirety, and by the plant in its smallest constituent parts.
Though it is difficult to point to any plant or any part of a
plant that does not seem to undergo this so-called rest-period,
I am inclined to think that nature often merely cloaks, but
does not suspend the processes of growth. With fruits such
a period of repose, if it exists at all, must be very brief ; and
with the great majority of seeds, which soon lose their vitality
on being dried, I should be disposed to believe that the
period between the cessation of active growth and the com-
mencement of loss of vitality must be very short.
Such are some of the considerations that present them-
selves when we reflect that the immature fruit holds more
water than the ripe fruit. They illustrate the great significance
that lies behind all experiments even of the simplest nature,
THE HOMOLOGIES OF FRUITS
269
such as are represented in the following two tables. The story
of the Acorn, viewed from the standpoint offered by the r61e
taken by the water-contents, seems to be particularly suggestive,
especially in connection with the tendency to vivipary at times
displayed, a subject discussed in Chapter XIX. Some of the
most fascinating problems bound up with plant-life lie behind
the phenomena of the drying fruit ; and none are more
important than that connected with germination on the plant.
In this respect the story of the decrease in the water-
contents of the Ivy berry (Hedera Helix\ as it grows steadily
from the autumn through the winter, finally dropping to the
ground in the spring, and often with one or more of its seeds
germinating, is particularly interesting. This progressive
decrease is clearly shown in one of the following tables. But
TABLE SHOWING THE DIFFERENCE IN THE WATER- CONTENTS OF IM-
MATURE AND MATURE FRUITS, AS INDICATED BY THEIR Loss OF
WEIGHT WHEN DRIED IN AIR UNDER ORDINARY CONDITIONS.
(By mature fruits are meant those that are full-grown and moist, contain ripe seeds,
and show no signs of drying. By immature fruits are usually meant those that have attained
nearly the full size and weight, but have seeds with contents not set or incompletely
developed. For the berries of Sambucus nigra another explanation is required, as is
given below. )
Average weight of
Loss of weight when dried
moist fruit in grains.
in air stated as a percentage.
Type of
fruit.
Immature.
Mature.
Immature.
Mature. '
Iris Pseudacorus .
200
250
85 per cent.
74 per cent.
Capsule.
,, fcetidissima
130
170
83
75
,,
^Esculus Hippocastanum
600
700
82
76
>>
(Horse-chestnut)
Hura crepitans
3000
3200
86
64
Phaseolus multiflorus
270
300
82
75
Legume.
Faba vulgaris (Broad
650
750
85
74
ii
Bean)
Guilandina bonducella .
340
400
Si
75
,,
Hedera Helix (Ivy)
i '7
5*5
79
63
Berry.
Quercus Robur (Oak) * .
10
60
77
68
Nut.
Sambucus nigra (Elder)t
3
3
87
78
Berry.
* The browning acorn is taken as the mature stage (see Chapters XIV and XIX).
t In the case of Elder berries the difference is due to the formation of sugars in the
ripening fruit, as explained in an earlier page of this chapter.
2 JO
STUDIES IN SEEDS AND FRUITS
the data there supplied only illustrates one of the features in a
process that in the Ivy berry often terminates in germination
on the plant. Matters more directly relevant to the subject of
vivipary in this plant, especially those concerning the growth
of the seed and its embryo, will be dealt with in detail in
Chapter XIX.
The decrease in the water-contents of a growing fruit
naturally involves the increase of the solid constituents. How
fruits gain in solids as they grow is well brought out in ths
general table immediately preceding these remarks, and with
TABLE SHOWING THE GRADUAL DECREASE IN THE WATER-CONTENTS OF
ACORNS (QUERCUS ROBUR) AS INDICATED BY THEIR Loss OF WEIGHT
IN DIFFERENT STAGES OF THEIR DEVELOPMENT WHEN DRIED IN
AIR UNDER ORDINARY CONDITIONS. (The cupule is not included.)
Date of
collection.
Condition of fruits.
Average weight
of a fruit in
Loss when dried
in air, taking
the moist fruit
grains.
as 100.
Aug. 24, 1910
Sept. 13,
\ Firmly attached by living
/ tissue to cupule
10
3 2
77 per cent.
74
2O >
Still firmly connected
46
72
,. 27.
Connection a little looser,
5
65
nuts browning.
Oct. 4,
do.
55
61
,, ",
Connection slight
51
4*
'8,
Browned ; fall at a touch
57
48
After two months, when
3
oo
air-drying complete.
Sept. 4, 1908
Firmly attached to cupule
56
75
17,
Still firmly attached
6z
68
. 3>
do.
62
54
Oct. 6, ,,
Connection slight ; nuts
7
51
browning.
v Z 4i
Browned ; fall at a touch
64
43
After two months, when air-
40
oo
drying complete.
This table is only intended to illustrate the decrease in the water-contents. At the
same time a rough idea can be formed of the progressive changes in the average weight
of an acorn, which is all that the method of the experiment will allow. The acorns of
each series were obtained from the same locality. It will be noticed that the acorns of
1908 were considerably heavier and larger than those of 1910. Ten fruits were used in
each case. For other data relating to the ripening and drying of the fruit the reader
should consult Chapters XIV, XIX, etc.
THE HOMOLOGIES OF FRUITS
271
special detail for the Acorn and the Ivy berry in the two
additional tables. These tables speak for themselves, and there
is no necessity to push the subject further here.
TABLE SHOWING THE GRADUAL DECREASE IN THE WATER-CONTENTS OF
IVY BERRIES (HEDERA HELIX) AS THEY DEVELOPED AND MATURED
AT REDLAND, BRISTOL, DURING THE WINTER 1908-1909.
(The collections were made by my sister, Mrs H. Mortimer, from the same plant and
weighed by her at once, the samples containing from forty to sixty berries. They were
weighed again by the author some months after. )
Changes of weight of an average berry when
Date of
Condition of
dried in ordinary air-conditions.
collection.
fruits.
Stated in grains.
Stated as a percentage.
Moist. Dry.
Moist. Dry.
Nov. 9
All green
1*69 o'36
IOO 21
,, 18
11
2'86 o'6i
100 21
Dec. 3
it
4*02 0*98
IOO 24
Two - thirds \
,, i?
green, rest }-
black J
4*96 1*46
ioo 29
Jan. 9
All black
5 '44 i '93
loo 35
>, 2 4
5*50 2'o6
ioo 37
Feb. 21
4' 10 1*64
ioo 40
Mar. 19
4*02 i '58
ioo 39
Observation at Salcombe, Devon.
May 1 6
ii
4 '60 2 'oo
ioo 43
Note. The reader is referred to Chapter XIX for other details respecting the growth
of the seed and its embryo.
SUMMARY
(1) Some of the most interesting problems connected with plant-
life lie behind the phenomena of the drying fruit.
(2) But a comparative study in this direction brings to the front
preliminary considerations of importance, more especially those
concerned with the lack of true adjustment which prevails in the
general classification of fruits and with the comparison of fruits in the
different stages of their history (p. 259).
(3) Observation on the drying of fruits shows us that when the
systematist speaks of a berry as fleshy and indehiscent and a capsule as
dry and dehiscent, he is contrasting a living with a dead fruit (p. 260).
(4) We come also to discover the fallacy that may lie in the
distinction between succulent and dry fruits, especially when it implies
272 STUDIES IN SEEDS AND FRUITS
a contrast between a moist living fruit that has yet to dry and a fruit
that has more or less completed the drying process and is to a greater
or less degree devitalised (p. 260).
(5) The tabulated results of the author's observations on the drying
of fruits in air indicate that nature does not recognise this distinction
between moist and dry fruits, all mature living fruits being moist fruits.
The contrast which the systematist draws between the fleshy drupe of
Prunus and the dehiscing, dried, or drying fruit of Datura is not the
contrast nature offers. Nature as interpreted through the balance tells
us that the full-grown moist and living capsule of Datura Stramonium
contains just as much water as the ripe drupe of Prunus communis^ and
that the dried and dead open capsule of the one could only be
compared with the dead and shrivelled drupe of the other (p. 261).
(6) These misconceptions lead to others. Thus, it is usually
implied that dry dehiscent fruits, like typical capsules and legumes, open
only when they are ripe, an assumption that involves us in much
confusion between the maturing, dehiscing, and drying stages of fruits.
How much we may err in this respect is indicated in Chapter XIII,
where it is also shown that ripe capsules and ripe legumes are all moist
fruits as far as their water-contents are concerned, and that whilst the
capsule dehisces in the living, moist state, the legume opens in the dried
and dying condition (p. 262).
(7) Amongst the points brought out in the tables are the large amount
of water in full-grown, living, woody fruits, and the manner in which the
drying of fruits is retarded by the presence of sugars and oils (p. 265).
(8) Some curious considerations also arise from the fact that
immature fruits contain more water than mature fruits. But this
progressive change in the water-contents as the fruit passes from
immaturity, when it contains, we will say, 80 per cent, of water, to
maturity, when the amount would be about 70 per cent., and thence
on to the drying stage accompanying its loss of vitality, when it retains
only the water of hygroscopicity, probably about 15 per cent., is
characteristic of all vegetable matter (p. 267).
(9) At first during active life this decrease is only relative and is
due to the more rapid increase of the solids. In the latter stage, when
the plant dies, it is absolute and involves the loss of all the water
required for the active processes of vitality. The occasional vivipary
of the acorn on the Oak and of the seeds of the Ivy berry (Hedera) on
the plant is in part an expression of the principle that the mature fruit
contains less water than the immature fruit (p. 269).
(10) The increase in the solid constituents of a growing fruit as
the water-contents decrease is well brought out in the tables, in one
table for a variety of fruits, in another with special detail for the acorn
and the Ivy berry (p. 270).
CHAPTER XIII
THE DEHISCENCE OF FRUITS
ONE is apt to associate the process of dehiscence with dryish
fruits, neither very soft nor very hard, and justly so, because
many opening fruits belong to this category. Both the capsule The capsule
and the legume are classed amongst dry fruits ; and the
implication often is that their dehiscence is connected with J
the relief of strain produced by unequal contraction during drying,
the drying of the fruit. My observations indicate that this
applies more especially to fruits like legumes, that often only
dehisce after they have been considerably dried, and that as a
rule it does not concern capsules. The incorrect conception
seems to be due in the case of capsules to the tendency to
regard as one and the same process the loosening of the cohesion
between the valves or carpels, which may take place when the
green fruit begins to mellow, and their subsequent drying,
when the fruit is rapidly losing its vitality. The sudden relief
of tensions generated by drying in the latter part of the dehis-
cence, resulting as it sometimes does in the forcible expulsion
of the seeds, produces effects that often emphasise the influence
of drying in the latter stages of the process, and is apt to favour
the idea that dehiscence is merely a matter of desiccation.
Thus, in Viola ) the breaking down of the cohesion between Capsules
the valves is one thing, whilst the subsequent folding inwards unde^mfist
of the edges as the valve dries up is another. Whether the conditions
& . where dry-
dipping" and forcible propulsion of the seeds are purposive ingispre-
or merely accidental can only be determined after an extensive
273 1 8
274
STUDIES IN SEEDS AND FRUITS
Viola.
^Esculus
Hippo-
castanum
(Horse-
chestnut)
and Iris.
comparative study of different fruits in all their stages. That
which concerns us here is the circumstance that Viola capsules
will dehisce under moist conditions without any drying what-
ever, and without any of the display of the results of elastic
tension which that process engenders. If we place a detached,
full-grown green fruit in wet moss, the first stage of dehiscence,
namely, the loosening of the cohesion between the valves, will
be accomplished without any drying, whilst the curling in of
the edges of the valves will be inhibited.
This is what happened in my experiments on the fruits of
the Garden Pansy (Viola tricolor] ; and one may contrast with
such results, where dehiscence takes place without any drying,
those results for the same plant where drying plays a
prominent part in the opening of the capsule, as given below.
THE DRYING AND DEHISCENCE OF A DETACHED RIPE CAPSULE OF
VlOLA TRICOLOR, WEIGHING FOUR GRAINS, THE RESULTS BEING
STATED IN PERCENTAGES.
Full-grown green
fruit (4 grains).
Beginning to de-
hisce (z'8 grains).
Valves lying back
(2 '6 grains).
Valves folded on the
seeds and dry ( i '6 grain).
100
70
66
40
Again, if we take a number of full-grown but still closed
capsules of sEsculus Hippocastanum (Horse-chestnut) and of
Iris Pseudacorus, and place some in wet moss and others exposed
to the free air on a table, we obtain the following results. In
a few days several of those on the t&ble will be found to be
opening after losing 25 or 30 per cent, of their weight ; whilst
those in the wet moss which have not dried at all but have
probably added to their weight will be also dehiscing. The
detached capsules of Iris fcetidissima illustrate the same thing
more forcibly, since they dehisce in wet moss, but fail
altogether to open when allowed to dry. Drying, therefore,
though it develops strains, the relief of which ends in the
dehiscence of fruits, is not a necessity for their opening. It is
THE DEHISCENCE OF FRUITS 275
essential in the latter stages, if the parts of the fruit are to
acquire the elasticity concerned in the forcible expulsion of the
seeds, but it is not necessary for seed-liberation. Seeing that
most fruits liberate their seeds without forcibly discharging
them in this manner, it may be doubted whether we should
specially regard such violent propulsion as purposive,
determined as it is largely by the degree of dryness of the air.
However this may be, it is evident from the above experi-
ments that other factors than those concerned with drying go
to determine the dehiscence of fruits.
Though the phenomena are physical in origin, writes Pfeffer Prof. Pfeffer
(Physiology of Plants, iii. 146-153), the development of the hiscence.
requisite physical conditions is a physiological problem. The
required instability, when mechanical agencies of external or of
internal origin may release the dehiscing organism, is produced
by growth, the requisite tissue-strains and the conditions for their
release being prepared by the vital activity of the organism.
The distinction which he draws between internal and external
agencies in the opening of dehiscent fruits coincides with one
of the principal differences between the modes of dehiscence
of legumes and many capsules, as indicated by my observations.
Whilst in the one case the opening of the capsule is often
brought about through the distension of its walls by the growth
of its seed-contents, in the other the dehiscence of the legume
is usually caused by the strain generated in the drying process. The author's
T , i A i_ j i_- 1 j observations.
In the capsule the dehiscence, however arising, corresponds
with the maximum growth of the fruit. In the legume it
happens at a much later stage, namely, after its biological
connection with the parent has been more or less severed,
and when it has lost the greater part of its water by drying,
and in consequence its vitality. Regarding the difference The capsule
between the two processes from merely a physical standpoint, dries^The
we can say that whilst the capsule dehisces and dries, the legume dries
* . r .... and dehisces,
legume dries and dehisces. By removing a single letter we
can at the same time express the biological distinction by say-
ing that whilst the capsule dehisces and dies, the legume dies
2 y6 STUDIES IN SEEDS AND FRUITS
and dehisces. With the capsule, therefore, the mechanism of
dehiscence is concerned with a living fruit. In the legume it
has to do with a dead one.
Thepre- In both the green capsule and the green legume there is
mTnowing generally a preliminary mellowing stage, corresponding, as
stage. shown in Chapter XI, to the ripening of the berry ; but it may
be transient or disguised by other changes, more especially
with the legume. It marks the completion of active growth
and indicates seemingly the commencement of the severance
of the biological connection between the fruit and the parent.
In this mellowing stage the green fruit often assumes a
yellowish tinge or a paler hue, and its tense, turgid appearance
gives place to one of relative flaccidity. Its firm, rigid walls
become softer and more yielding, and the cohesion along the
sutures is loosened. This is best exemplified in the capsule,
though the same may be noticed in legumes, as in the Pea.
But whilst with the capsule the immediate result is the dehis-
cence of the fruit, with the legume no such effect is produced
at that stage, and dehiscence occurs at a much later stage as a
relief from the tension produced from outside by the drying
up of the pod.
Observations I will now refer to some of my observations on the opening
hiscenceof of capsules on the living plant, and will begin with Iris
fatidissima. This plant, growing as it often does in more or
plant less shady woods, offers one a better chance of eliminating
the drying factor than does Iris Pseudacorus, which frequents
more exposed situations. Though the mellowing stage is not
so easily recognisable as in the species last named, we can
detect the approach of dehiscence in the lessened turgidity of
Iris foetid- the green fruit and in its paler hue. The capsules, when
they display the earliest signs of their opening (a slight
separation of the valves at and near the apex) are quite
moist fruits and show no signs of drying. But, once
begun, the process is rapidly completed by drying, and in
a few days the valves stand well back, exposing the bright
scarlet seeds. That the first rupture is due to some cause
THE DEHISCENCE OF FRUITS 277
acting from within, such as the pressure of the seed-contents,
is highly probable. Full-grown fruits placed in water and
in wet moss commenced to dehisce in a few days, whilst
others left to dry on a table made no effort to open after
prolonged drying.
With Iris Pseudacorus careful observation of the living Iris Pseuda-
plant convinced me that dehiscence as a rule occurs in moist,
mellowing fruits, that is to say when the green capsule assumes
a yellowish tinge. Although, as already observed, the detached
fruits will dehisce in wet moss, this does not exclude altogether
the participation of the drying factor in the plant's natural
station by the water-side, where it is fully exposed to the sun.
If fruits dehisced in my experiments without drying, some of
them also opened after they had lost about 25 per cent, of
their weight exposed on my table. Nature does not follow
formularies in such matters ; and though internal causes mainly
determine the early dehiscence, we cannot entirely disregard
the influence of external conditions. The stages in the history
of the dehiscence of fruits normally maturing in September
would seem to be as follows :
(1) The full-grown green capsule, firm, full, and turgid ;
(2) The capsule mellows, becoming yellowish and rather
softer, which results in loosening the cohesion
between the valves ;
(3) The dehiscence begins, determined by the pressure of
the seed-contents, but aided by exposure to the sun
and by buffeting in the wind ;
(4) The rapid drying of the fruit and the full exposure of
the seeds.
The results of one method of proving that capsular fruits A proof that
dehisce in the moist condition are given in the subjoined deSfsceln
table for Iris and for the Horse-chestnut. Here we find the ?ist
condition.
that the fruit showing the first signs of dehiscence loses
but slightly less in weight when dried in air than does the
full-grown moist fruit with matured seeds that has not begun
to open.
278
STUDIES IN SEEDS AND FRUITS
Scilla
nutans.
The normal
dehiscence of
an actively
growingfrait
impossible
for physio-
logical
reasons.
TABLE SHOWING THE Loss OF WEIGHT WHEN DRIED IN AIR OF FULL-
SIZED, MOIST, CAPSULAR FRUITS, BOTH BEFORE DEHISCENCE AND
IN THE EARLIEST STAGE OF DEHISCENCE, THE DEHISCING FRUITS
BEING GATHERED IN THAT CONDITION FROM THE PLANT.
Full-sized fruits before
dehiscence.
Fruits beginning to
dehisce.
74 per cent.
70 per cent.
ye
7-1
^Esculus Hippocastanum .
76
69
Note. The average was taken of from five to ten fruits in each case.
But it is often very difficult, by observing capsular fruits
on the plant, to eliminate the drying factor ; and the most we
can often say in such cases is that dehiscence takes place in
the living fruit before the drying is very evident. In the case
of Scilla nutans , for instance, we find the full-grown green
capsule in a condition of strain, not, however, on account of
the pressure of the enclosed seeds, since they only partly fill
the cells, but through the turgidity produced by active growth.
Though green and moist, it ruptures with a " pop " when
squeezed between the fingers. A little later the fruit becomes
paler, looks a little dryer, and its turgid appearance has dis-
appeared. If we press it gently, there is no longer an elastic
resistance, and the valves, though still in position, are seen to
be partially disconnected. The fruit has dehisced, although
still green and fairly moist, and only the pressure of the finger
reveals what has occurred. Here it seems impossible to
separate the dehiscence from the early stage of drying ; and
yet the loosening of the cohesion between the valves was
probably effected in the mellowing stage when the firm, turgid
green fruit became softer and almost flaccid. On physio-
logical grounds I would suppose that the dehiscence of a green
fruit in active vitality could never be normally produced either
by internal or external causes, and that dehiscence could only
occur after the biological connection with the parent begins to
be severed. This I take to be the mellowing stage of fruits,
THE DEHISCENCE OF FRUITS 279
pronounced in berries, much less evident in capsules, and
often more or less disguised, or very slight, in legumes.
It is likely that the behaviour of the fruits of Scilla nutans
is typical of many capsules but partially filled by their seeds.
We will take the case of Stellaria Holostea. Here, as with Stellaria
fruits in general, the development of the fruit is far in advance
of the seeds. In its early stage, when about the size of a small
pea, the capsule is little more than an empty bladder, since the
young seeds do not occupy one-tenth part of the cavity. But
when the green fruit is full-grown, it is loosely but not entirely
filled by its soft white seeds, so that there is no pressure on the
capsular walls from within. Afterwards, as the fruit dries, the
seeds shrink and only half fill it. The valves, though still in
position, become disconnected at the edges, as a slight pressure
of the finger will show ; but there seems to be no reason why
they should be sundered in the drying process, since they
remain in position ; and it would appear probable that the
coherence between their edges was broken down, as in Scilla
nutans, when the biological connection of the fruit with the
parent first began to fail.
Assuming that the first preparation for dehiscence is
accomplished when the capsule ceases active growth and begins
to mellow, then we perceive that the next cause of the actual
disconnection of the valves may vary according as the seeds
completely or only partially fill the cavity. In the first case, Thejdehis-
as with Iris, the capsular walls, owing to the loosening of the completely
connection between the valves, are no longer able to respond fi ]^j a jj cd
to the pressure of the seed-contents by increased growth, ripe capsules.
They yield at the weakened sutures and the fruit dehisces, the
valves as they wither and dry falling back and exposing the
seeds. On the other hand, when the capsule is not full of
seeds, so that there is no distension or pressure on the walls
from within, the cohesion between the valves is still loosened
in the mellowing stage, but they remain in position during the
early part or most of the drying.
A few remarks may now be made on some other capsules.
280
STUDIES IN SEEDS AND FRUITS
Those of Arenaria peploides behave like the fruits of Stellaria
Holostea above described. Although detached capsules of
Datura Stramonium lost 18 per cent, of their weight in my
experiments before they dehisced, it is highly probable that,
like those of Iris, when kept in wet moss they would have
opened without any drying at all. In the same way the moist
mature fruits of the Primrose (Primula verts), after lying one
night on my table, were found to be dehiscing and to have lost
about 20 per cent, of their weight. But observation of the
capsules on the living plant led me to consider that the first
stage in dehiscence begins still earlier in the drying process. It is
singular that the normal opening of the Primrose capsule at the
top may be prevented by making a hole in its base. Appended
are the results of my observations on the dehiscence of detached
mature capsules of Primula verts and Datura Stramonium, when
allowed to dry on my table. Though obviously such experi-
ments are not carried out under nature's conditions, their results
will serve to illustrate the early opening of capsular fruits.
THE DRYING IN AIR AND DEHISCENCE OF DETACHED RIPE
CAPSULES OF DATURA STRAMONIUM AND PRIMULA VERIS.
Average weight in
grains of a ripe
moist fruit.
Loss of weight, the ripe un-
opened fruit being taken as 100.
Before
dehiscence.
When de-
hiscence
begins.
After the
drying is
complete.
Datura Stramonium
Primula veris
350-0
3'5
IOO
100
|
80
30
3
In a species of Aquilegia growing in my garden the opening
of the follicles took place shortly after the period of maximum
growth. The green follicles are completely closed ; but as
they ripen they acquire a purplish tinge and gape open at the
base before normal dehiscence occurs. In such mature fruits
the cohesion at the ventral suture becomes very slight, and a
slight increase of the tension due to some external cause would
THE DEHISCENCE OF FRUITS
281
Contrast in
the water-
contents of
capsules.
bring about the separation. I found that the follicles just
beginning to dehisce were usually the heaviest.
Dehiscence may take place in the most watery of capsules,
as with those of Momordica^ where 95 per cent, of the fruit
(excluding the seeds) consists of water, and in the hardest and
most ligneous of capsules, as with those of Mahogany (Swietenia
Mahogani\ where the woody walls hold only about 66 per cent,
of water and are 10 millimetres or nearly half an inch thick.
The dehiscence of the fruits of a species of Momordica observed Momordica.
by me in Jamaica (seemingly a cross between M. Charantia
and M. Eahamina] was quite regular, and took place when the
fruits were ripe and moist. After the seed-contents were
removed, a ripe fruit not yet beginning to open lost 94 per
cent, of its weight when dried in air, whilst a similar fruit just
beginning to dehisce lost 91 per cent. The first stage in
dehiscence seems to be due to the tension produced in the
walls of the softening fruit by its contents. With the woody
fruits of Mahogany the exact stage at which dehiscence occurs Mahogany,
on the tree is not easy to determine ; but one can get an
approximate idea. The full-grown green fruits, which seem
to average about four-fifths of a pound in weight (5600 grains
or 363 grammes) lose about two-thirds of their weight when
detached and allowed to dry for several months, but they begin
to open when they have lost about one-fourth of their weight.
DRYING IN Am OF A DETACHED, GREEN, FULL-GROWN CAPSULE (NOT
YET DEHISCING) OF MAHOGANY (SWIETENIA MAHOGANI), INCLUDING
SEEDS.
Condition of fruit.
Weight in grains.
Percentage.
Green, full-grown, not yet dehiscing .
The same fruit beginning to dehisce
on my table
The same fruit after drying for months
5900
4370
2030
lOO'O
74'i
34'4
Dehiscence will probably occur also if drying is prevented, as shown below.
These results for the drying of a detached fruit of Ma-
hogany are, as far as dehiscence is concerned, very much the
282 STUDIES IN SEEDS AND FRUITS
same as those obtained for detached fruits of Iris Pseudacorus and
ALsculus Hippocastantim (Horse-chestnut), which dehisced in my
room after losing 25 or 30 per cent, of their weight. It has,
however, been shown that in both these cases dehiscence occurred
in wet moss when drying was prevented, and it is very probable
that Mahogany capsules would behave in the same way.
In the above experiment the fruit was dried in the entire
condition. Closely similar results were obtained in drying a
fruit that had been taken to pieces. The original total weight
of the green fruit was 5576 grains, and the weight after the
drying-in-air was completed was 1996 grains, the proportions
being as ioo'O to 35*8.
Ravenala. The dehiscence of the fruits of Ravenala madagascariensis
(Traveller's Palm), as observed by me in plants growing near
the rest-house on the Grand Etang in Grenada, presents
another type of the opening of capsular fruits. We are here
concerned with a sub-drupaceous capsule displaying loculicidal
dehiscence. Within the outer moist husk is a bony endocarp
or " stone," which even in the fresh fruit requires a heavy blow
to break it, and is 5 or 6 millimetres thick. The dehiscence of
this fruit raises a number of questions which are dealt with in
other chapters. Not the least important of them are the propor-
tion of parts and their several water-contents, and especially
the failure of the young seeds, which is here quite phenomenal.
With regard to the failure of the young seeds, reference
will also be made to the subject in Chapter XVI. Here I will
Its dehis- merely allude to it in connection with the fruit's dehiscence.
The full-sized seeds vary from 9 to 15 millimetres in length ;
but there is only room in each of the double spaces of the three
compartments for from three to five, making a possible total
ranging from eighteen to thirty seeds. But even this is often
never reached. The fruit figured in Schumann's monograph
below referred to probably did not contain more than fifteen
seeds. Amongst those fruits examined by me there were not
uncommonly only one to three full-grown seeds in each valve, or
from three to nine or ten in all. All the rest of the fruit-cavity
THE DEHISCENCE OF FRUITS
283
is occupied by numerous aborted seeds, 3 to 5 millimetres long,
and varying from twenty or thirty to forty or fifty in number.
This tremendous waste, not of ovules, but of seeds that could
find no room for further development, plainly indicates the
existence of a great tension within the living fruit. If the stony
walls by their pressure are able to prevent the proper growth of
all but a very few seeds, they are subjected in their turn to the
opposing strain of the expanding seeds ; and in the end the
seeds are successful in rupturing the walls, though too late for
the maturation of most of them. This is evidently what happens
on the tree, since it is the moist fruits that are found dehiscing.
The first stage in the dehiscence of Ravenala fruits is therefore
due to the expansive force of the growing seed, and drying does
the rest. One may note in passing that the genesis of the thick,
tough walls of this and other capsular fruits may lie in its being
a response to the expanding pressure of the growing seeds.
That drying is a potent factor in the completion of the
process is shown in the behaviour of the " stones " of Ravenala
when allowed to dry after being removed from ripe, unopened
fruits. They begin to split loculicidally when they have lost
about 1 5 per cent, of their weight, but some also split septi-
cidally at the apex of the valves, the loculicidal dehiscence
ultimately prevailing. The loss of water during the drying in
air of the entire fruit may here be given, though the subject is
also dealt with in tables given in Chapters XII and XIV.
RESULTS OF DRYING IN AIR A FRESH FRUIT OF RAVENALA
MADAGASCARIENSIS.
Fresh fruit.
Air-dried fruit.
Loss of
weight in
drying.
Weight in
grains.
Percentage
of entire
weight.
Weight in
grains.
Percentage
of entire
weight.
Skin and husk
Stone with seeds
Entire fruit
268
452
720
37-2
62-8
lOO'O
49
252
301
16-3
83-7
lOO'O
8 1 7 per cent.
4O ,,
58-2
The loss of weight of the stone without the seeds would be about 40 per cent.
The water-
contents of
full-grown
capsules
tabulated.
284 STUDIES IN SEEDS AND FRUITS
Excellent illustrations of the fruits of Ravenala are given
by Schumann in his monograph on the Musaceae (Das
Pflanzenreich, iv. 45). He, however, figures only the dry
fruit, as his description of eine holzige Kapsel would also imply.
The ripe fruit before dehiscence is yellowish and moist, and
it is only when it dehisces, dries, and turns brown that the
woody texture is disclosed.
The contrast above drawn in the case of such different
kinds of capsular fruits as Momordica, with 95 per cent, of
water, Mahogany, with about 66 per cent., and Ravenala, with
about 62 per cent., leads one to compare these extreme examples
with other capsules as regards their water -contents. The
subject is discussed for fruits in general in the following
chapter. The data tabulated below are merely intended to
illustrate the great variation in the amount of water held
by capsular fruits when full-grown, and before they begin
to dehisce and dry, the seeds being for the convenience
THE WATER-CONTENTS OF FULL-GROWN CAPSULES BEFORE DEHIS-
CENCE AND DRYING COMMENCE, THE SEEDS BEING EXCLUDED.
Water-contents stated as a percentage.
Weight in
grains of
full-grown
Total, including
capsules,
Loss when dried
the water driven
excluding
in air without
off at 100 C.
seeds.
heat.
(Estimated : see
below.)
Momordica Charantia
600
94 'o per cent.
95*0 per cent.
Scilla nutans
7
93-0
94 -o
Datura Stramonium
220
87-0
89-0
Iris Pseudacorus .
130
86-4
88-4
Ipomoea tuba
35
86-0
88-0
Arenaria peploides
^Esculus Hippocastanum (]
lorse
17
440
84-6
84-0
87-0
86-3
chestnut)
Primula veris ( Primrose)
17
83-8
86-0
Canna indica
36
82-6
84-8
Iris fcetidissima .
70
787
82-0
Aquilegia (species of) .
*7
76-8
80 -o
Thespesia populnea
150
76-3
79'3
Swietenia Mahogani (Mahogany)
4800
62-6
66-3
Ravenala madagascariensis *
700
58-2
62-5
The seeds are here included, but their influence on the total result is small.
THE DEHISCENCE OF FRUITS 285
of comparison excluded, except in one case there explained.
In spite of the contrast between the fruits of Momordica and
S cilia on the one hand, and those of Swietenia and Ravenala
on the other, the driest of these mature fruits contain a
large amount of water.
Notes on the above table. The total water of the fruit as
given in the last column is estimated by applying a correction
to the air-dried residue. Although the result is only approx-
imate, the limits of error, as will be seen, are small. The
water driven off in the oven after living vegetable substances
have been air-dried is the water of hygroscopicity possessed
in common by both living and dead matter (see Chapter VII).
According to my observations, this varies usually from about
10 percent, for air-dried, stony fruits to about 15 per cent,
for loose-textured, air-dried fruits, such as ordinary legumes,
capsules, and nuts, the seeds being excluded. Thus, in the
case of Momordica, the air -dried residue of 100 grains of
fresh material would weigh 6 grains. In the oven, exposed
to a temperature of 100 C., this residue would at the most
lose 1 5 per cent, of its weight and would be reduced to nearly
5 grains, so that the total water in the fresh material would
amount to about 95 per cent. In the same way, if, as is
probable, the air-dried Mahogany capsule lost 10 per cent.
of its weight in the oven, the air-dried residue of 37*4
grains out of 100 grains of fresh material would be reduced
t 33*7 grains, so that the total water held by a living
Mahogany capsule, excluding the seeds, would amount to
66'3 per cent.
It will have been gathered from the preceding remarks,
as well as from the indications afforded in the table just given,
that when we speak of a capsule as a dry fruit, we have usually
in our mind dehiscing capsules, which have been more or Dehiscing
less completely severed from the parent as far as the biological being dead
connection is concerned. Dehisced capsules now appear as or dying,
belong 1 only
dead or dying fruits ; and although even the toughest and to the
.. . ill j i i c herbarium,
most ligneous among them hold a considerable amount or
286
STUDIES IN SEEDS AND FRUITS
Structural
characters
cannot be
concerned
with the
liberation of
seeds from a
dead fruit.
water when full-grown and before dehiscence on the plant,
as dehiscing fruits they give up the greater part of it to the
air, only retaining what is common to both dead and living
organised vegetable substances, the water of hygroscopicity.
All dehiscing capsules, whether they originally possessed in
the full-grown, unopened condition on the plant as much
as 94 or 95 per cent, of water, as in S cilia and Momordica, or
as little as 62 or 66 per cent., as in Ravenala and Mahogany,
should be classed with dry fruits when they present themselves
in the act of freeing their seeds on the plant. It is very
questionable whether the expression " dry fruit " has any
significance except for the herbarium. Consistently applied,
it has no biological value, since the living connection with
the parent plant has been severed.
Let us take the dry, dehiscing fruits of Canna, Iris, and
Datura, which, as we observe them on the plant, certainly
deserve that appellation, though they have lost their vitality.
When full-grown on the parent and ready to dehisce, they
contain (excluding the seeds) from 80 to 90 per cent, of
water ; and their soft seeds, as shown by actual experiment
on those of Iris Pseudacorus, are able to proceed at once with
germination without the interruption of a rest-period. Such
are the fruits with which the student of the living plant is
chiefly concerned. The dry, dehiscing capsule belongs only
to his herbarium. So it is with legumes, as will subsequently
be shown, and so it is with the shrivelling berry. All that
is purposive ends when a fruit has passed its prime. The
fruit dies, let it be a capsule, a legume, or a berry ; and
the mode of liberation of its seeds depends on structural
characters that were developed when it was a part of a
living plant, and could have had no possible concern with
the escape of the seeds from a dead fruit. All appear-
ances of adaptation to seed-dispersal in fruit-dehiscence are
delusive and based on a one-sided view of the subject.
We observe all those cases where Nature seems to give
her aid and ignore the multitude of others that she seems
THE DEHISCENCE OF FRUITS 287
to leave alone. Nature, as we should read her story, is
indifferent to all. The distribution of seeds by dehiscing
fruits thus presents itself as determined by the laws con-
trolling the disintegration of dead organised matter ; and
in this disintegration the loss of the water necessary for
the fruit's vitality occupies an early stage. It is with the
drying of fruits biologically severed from the parent plant
that the discharge of seeds by capsules, legumes, and other
similar fruits is usually connected.
As previously pointed out, the typical dehiscence of Thedehis-
n 11/1J- cence of a
legumes occurs at or near the close or the drying process, legume is the
(The opening can be easily prevented by placing the fruit in
wet moss, the valves ultimately falling apart through the decay
of the connecting tissues.) If, then, dehiscence takes place in
a capsule in a living fruit, it takes place in a legume in a dead
fruit ; and all the objections urged in the case of a capsule
against regarding the propulsive liberation of seeds as a special
adaptation apply even more forcibly to the legume. Late
dehiscence is evidently characteristic of all those numerous
legumes, with which the reader will be familiar, where the dry
valves spring apart suddenly (throwing the seeds often some
distance) and then coil up spirally. It is likely, as in the
capsule, that the first loosening of the connection between the
valves takes place when the fully developed green legume
begins to soften or mellow, a stage marking the beginning of
the severing of the biological connection with the parent and
the ushering in of the drying process. But though such a
change is often more or less disguised in legumes, it may
be recognised at times in the paler green colour, and more
conspicuously in those cases where, as with Ctesalpinia
sepiaria, the green fruit assumes a yellowish tinge. The
drying pod generally darkens or blackens, as in Vicia^
Lathyrus, C<esalpinia, Ulex, etc. ; but there are whole groups,
as with CafMva/ia, where the fruit as it dries becomes
lighter in colour and ultimately has a nondescript, parchment-
like appearance.
288
STUDIES IN SEEDS AND FRUITS
Method of
determining
the stage at
which dehis-
cence of
legumes
occurs, such
as those of
Vicia, Ulex,
and Cassal-
pinia.
As illustrating the dehiscence of typical legumes, I will take
the behaviour of the pods of Vicia sativa, Ulex europ<eus, and
C<esalpinia sepiaria, as determined by the balance. The plan
adopted was similar to that followed in the case of capsules like
those of Viola. The total loss of weight by drying of the
detached, full-grown green fruit was first ascertained and then
the loss of weight during parts of the process. Thus with
Viola capsules I found the loss of weight before and after
dehiscence began. With the legumes I checked the total loss
of weight during the drying of the green fruit by ascertaining
the average loss of weight after and before the pod had
blackened. By combined observation on these lines of the
detached fruit and of the fruit on the plant it is not difficult to
obtain an approximate result. With Vicia and Ulex the final
loss of water in the closing stage of the dehiscence immediately
resulting in the ekstic opening of the pod was determined by
placing the darkened or blackened, nearly dry pods, under a
glass in the sun, when they would all dehisce in an hour, and the
weights before and after the experiment were then compared.
The results given for the three typical legumes in the
table below are closely similar. We there see that the full-
grown moist pod on the plant loses on the average 59 per
cent, of its weight before dehiscence occurs, and that the
subsequent loss of weight is small, the total loss in drying
amounting to about 62 per cent.
TABLE ILLUSTRATING THE STAGE IN THE DRYING PROCESS AT
WHICH THE DEHISCENCE OF LEGUMINOUS PODS OCCURS.
Average
weight of a
green pod
in grains.
Changes in weight during drying, the
full-grown moist pod being taken as 100.
Green.
After turn-
ing black.
Still
closed.
After
dehiscence.
Vicia sativa
Ulex europaeus
Csesalpinia sepiaria .
15-0
2 '3
IIO'O
IOO
IOO
IOO
5
5
39-0
45-0
38*0
37-6
43'
33-0
THE DEHISCENCE OF FRUITS 289
One might mention a number of other legumes where,
although the balance was not employed in this connection, it
was evident that dehiscence occurred when the drying in air
was far advanced, such as Guilandina bonducella and Poinciana
regia^ the last tardily dehiscent.
The transverse dehiscence of legumes into closed joints or The trans-
articles also takes place towards the close of the drying process, cence of
I am most familiar with this form of opening in the case of En tadapods.
Entada scandens and E. polystachya. In this genus, to employ
the description employed by Grisebach in his Flora of the British
West Indian Islands^ the legume is " flat-compressed, the joints
separating from each other and leaving a persistent, continuous
border, the replum." The pods, when the drying is far
advanced, break up on the plant into closed joints, each joint en-
closing a single seed. With Entada polystachya this is generally
preceded by the scaling off of the epidermis. If the epidermis is
persistent, as happens at times, the pod remains entire. The ulti-
mate liberation of the seed is affected by the decay of the joint.
As far as the mode of dehiscence is concerned, the remark- The dehis-
able polycoccous capsular fruit of Hura crepitans might be Hura
almost described as composed of a number of single-seeded cre P ltans -
legumes arranged around and attached to a central axis. The
rupturing of the cocci takes place in the last stage of the
drying of the fruit. A fruit, seemingly dry, but displaying the
earliest signs of the splitting of the cocci, was placed in a box
and left in a warm corner. After the dehiscence was complete
I found that the fruit had lost about 8 per cent, of its weight
in the process. This fruit, which contained fifteen cocci,
weighed 1233 grains, and I was able to estimate its weight in
the green condition from the following data :
Actual weight of a green fruit with 14 cocci = 3062-5 grains.
l6 = 3 28l>2
Estimated 15 =3172-0
This reliable estimate of its weight in the green, full-grown
condition enabled me to complete the history of its dehiscence
19
290 STUDIES IN SEEDS AND FRUITS
by means of the balance. As shown in the results below
tabulated, the stage in the drying process at which dehiscence
occurred corresponds closely with that obtained for typical
leguminous pods of the genera Vida^ Ulex, and Ctfsalpinia, as
before given.
DRYING AND DEHISCENCE OF A FRUIT OF HURA CREPITANS.
(See above for explanation.)
Full-grown green fruit
(estimated).
On the point of
dehiscing.
After dehiscence.
Weight in
grains.
Percentage.
Weight
in grains.
Percentage.
Weight
in grains.
Percentage.
3172
100
I2 33
3^9
"37
35-8
But the resemblance between a coccus of Hura crepitans
and a leguminous pod is not merely concerned with the stage
at which dehiscence occurs, but also extends to the mode
of the dehiscence. Each woody coccus splits along the back
more or less completely into two valves, whilst at the same
time it detaches itself with violence from the central axis and
carries the seed away for many yards. After the rupture each
valve displays a very slight spiral twist, thus indicating that
the mechanism of dehiscence is similar to that of the legume,
which after its sudden opening shows two spirally twisted
valves.
SUMMARY
(1) One is apt to associate the process of dehisoence with dry
fruits, and both the capsule and the legume are usually classed among
dry fruits ; but the author's observations indicate that this association
applies more especially to fruits like legumes that usually only dehisce
after they have almost completed the drying process, and that as a rule
it does not concern capsules. Whilst the legume dehisces after drying,
the capsule dehisces before drying begins.
(2) The author's results bring him into line with the view
expressed by Professor Pfeffer that whilst the phenomena of dehiscence
THE DEH1SCENCE OF FRUITS 291
are physical, the development of the requisite physical conditions is a
physiological problem.
(3) Yet the different behaviour of capsules and legumes illustrates
the difference between external and internal causes in the dehiscence
of fruits. Whilst with the capsule dehiscence takes place in the
ripening fruit as a relief to the tissue-strains developed by growth, in
the legume dehiscence usually presents itself as a relief to the tensions
developed by drying. Whilst the capsule dehisces and dries, the pod
dries and dehisces, the mechanism being concerned in the first case
with a living fruit and in the second case with a dead one. Amongst
the capsular fruits especially studied in this connection were those of
/Esculus, Arenaria, Datura, Iris, Primula, Scilla, Stellaria, and Viola.
(4) Dealing particularly with capsules, it is considered that the first
step in the relief of the strain produced by active growth is promoted
by the loosening of the cohesion of the valves affected in the mellow-
ing stage of the full-grown moist fruit. It is held that the normal
dehiscence of an actively growing fruit is physiologically impossible,
and that dehiscence could only occur after the biological connection with
the parent begins to be severed in the mellowing process. The nature
of the next stage depends on whether the seeds completely fill the fruit
cavity, as in Iris, or only partially fill it, as in Scilla and Arenaria.
In the first case the capsular walls, owing to the loosening of the
connection between the valves, are no longer able to respond to the
pressure of the seed-contents and gape widely during the subsequent
drying process. In the second case the drying completes the loosening
begun in the mellowing stage, but the valves remain more or less in
position.
(5) Dehiscence may occur alike in the most watery of capsules, as
in Momordica, where the fruit-case holds 95 per cent, of water, and in
the hardest and most ligneous of capsular fruits, as with Mahogany
(Swietenia], where the water-percentage is 66, the dehiscence being
carried on in each case on the same regular plan as in Iris and in the
Horse-chestnut (Msculus). The dehiscence of the Mahogany fruit is
especially described, as well as that of Ravenala, another type of woody
capsule, in which last special questions are raised.
(6) The contrast just drawn between the water-contents of the
pericarp or fruit-case of fleshy and woody capsules leads to the
discussion of a number of observations on different fruits, and stress is
laid on the point that even the driest-looking and most ligneous of
capsules hold more than 60 per cent, of water in the full-grown living
state. When, therefore, we speak of a capsule as a dry fruit, we really
have in our minds the dry dehisced fruit that has lost its vitality.
Dehisced capsules thus appear as dead or dying fruits ; and the
expression " dry fruit " has in their connection no biological significance
292 STUDIES IN SEEDS AND FRUITS
for the student, the dry dehiscing capsule belonging only to his
herbarium. It is futile for him to look to the structural characters of
a dead capsule for evidence of adaptation to the dispersal of seeds.
The living fruit alone should be his study. The fruit dies, and the
mode of liberation of its seeds depends on structural characters that
were developed when it was part of a living plant and could have had
no possible concern with the ultimate escape of the seeds from a dead
capsule. All that is purposive ends when a fruit has passed its prime.
(7) In reference to the late dehiscence of legumes at or near the
close of the drying process, as compared with the early dehiscence
of capsules which occurs at or near the commencement of the same
process, it is pointed out that if dehiscence takes place in a capsule in
a living fruit, it occurs in a legume in a dead fruit, and that all the
objections urged in the case of a capsule against regarding the
propulsive liberation of seeds as a special adaptation apply even more
forcibly to the legume.
(8) The late dehiscence of legumes is then illustrated by the typical
cases of Vicia^ Ulex^ and Ccssalpinia.
(9) Finally, the transverse dehiscence of some legumes is briefly
referred to ; and the dehiscence of the polycoccous capsule of Hura
crepitans is described in detail, the behaviour of the opening fruit being
that of a number of single-seeded legumes around a central axis.
CHAPTER XIV
THE PROPORTION OF PARTS IN FRUITS
THE relation in weight between the pericarp and the seeds in
the different stages of a fruit's history now claims our attention.
This involves not merely a comparison of parts in the various
states, but a detailed examination of the shrinking process
which the moist, full-grown fruit has to undergo in entering
the air-dried state.
Amongst the first questions that offer themselves in an Therespec-
investigation of this kind is that concerned with the respective o/moisrtan
values of the moist and dry fruit for such comparisons. The df y fruits -
moist condition is naturally the most important, since the
fruit-covering or pericarp and the seed are still actively
functioning, whilst in the dry condition the fruit-case is dead
and the seed has its vitality suspended. It is true that the
systematist often employs the last-named condition of the
fruit ; but he has been under the whip of necessity ; and if
by so doing he has at times confused the issues as regards the
homology of fruits, he has been constrained by the circumstances
of his investigation. Yet it behoves us all the more to keep
the living fruit always in our mind. By so doing we can best
hope to avoid those false analogies and deceptive contrivances
which are so apt to be accepted as adaptive when we deal
indiscriminately with dead and living fruits.
The subject, however, is a very complex one, and Nature
herself does not always aid us by bringing the several processes
concerned in the maturation of fruits and seeds into a final
relation with each other. Thus, as already pointed out in
293
294
STUDIES IN SEEDS AND FRUITS
The method
of investi-
gation as
illustrated in
the case of
Chapter XL, the seeds shrink in the ripening berry. Then,
again, we shall see later on in this chapter how in the Acorn
(Quercus) the seed often continues its growth after the fruit-
shell has ceased to add to its weight and has begun to dry ;
whilst with the Coco-nut, when the husk of the drying fruit
is losing pounds in weight, the hard shell and the albumen
increase considerably in amount.
The method of investigation usually adopted may be best
illustrated in the case of the large husky fruits of Earringtonia
speciosa^ the experiments covering many weeks. (The materials,
Baningtonia ft should be remarked, were allowed to dry in my room in
speciosa. J , J
Grenada, except in the early stage or the drying process, when
they were exposed for a few hours daily in the sun.) The
first step consisted in determining the shrinking ratio of the
moist, full-grown fruit as shown by the difference in weight in
the moist and dry conditions. There were three ways of
obtaining this result :
(1) By comparing the average weights of moist and dry
fruits ;
(2) By drying the moist fruit in the entire state ;
(3) By drying separately the parts of the moist fruit,
namely, the husky pericarp and the seed.
By employing these three methods the following results
were obtained for Earringtonia speciosa :
The shrink-
age of the
fruit in the
entire
condition.
Method.
Shrinking ratio, taking the
moist fruit as 100.
Average of moist fruits (15 to zi ounces),
and of dry fruits (3 to 5 ounces)
Drying the entire fruit ....
Drying the fruit in parts
100 22
100 1 6
100 13
On account of the considerable variation in the size and
weight of the fruits of Earringtonia speciosa the results supplied
by the first method could only be regarded as roughly
approximate, and in consequence they were used merely as a
check. The drying of the fruit in parts was deemed to give
THE PROPpRTION OF PARTS IN FRUITS 295
results in excess of what would happen under natural conditions
which would be best imitated in the method of drying the
entire fruit. One or two reasons led me, when accepting the
result of the second method, to reduce it slightly, and the
shrinking ratio of 100 to 15 for the fruit was finally adopted.
The next step was to determine the separate shrinking
ratios for the pericarp and the seed of the moist fruit. In
spite of its husky appearance, the pericarp, like the husk of the
coco-nut, contains a very large amount of water. Two plans
were followed here, as below described.
(i) The relative weights of the husk and seed of the moist
and dry fruits were obtained, and the results were
applied to the shrinking ratio of the entire fruit as
above ascertained. In this manner it was found that
in the moist mature fruit the weight of the pericarp
constituted about 80 per cent, of the weight of the
entire fruit, whilst in the dry fruit it amounted to
about 50 per cent. Since the fruit attains its full
size far in advance of the seed, it was necessary to
select moist fruits where the seed had attained the
maximum weight.
The shrink-
age of the
separate
pericarp and
seed of
Barringtonia
speciosa.
Barringtonia speciosa.
Weight in grains.
Shrinking ratios.
Relation of parts.
Moist.
Dry.
Moist.
Dry.
Moist.
Dry.
Pericarp .
Seed
Entire fruit
8000
2OOO
10,000
75
75
1500
IOO
100
IOO
9 '4
37'S
15-0
80
20
IOO
5
So
IOO
(2) The actual shrinkage or loss of weight was obtained
separately for the pericarp and seed of the moist
fruit with the following results :
Ratio of shrinkage for the pericarp 100 to 10.
seed loo 40.
Supplementary observations on individual fruits led me to
the opinion that in the results of the first method the weight of
296
STUDIES IN SEEDS AND FRUITS
the moist seed was too great and its estimated shrinkage exces-
sive, whilst it also appeared that in the dry fruit the pericarp is
as a rule rather heavier than the seed. The requisite correc-
tions were not great, but they brought the various results into
harmony, and the final statement accepted was as follows :
Barringtonia speciosa.
Shrinking ratios.
Relation of parts.
Moist.
Dry.
Moist.
Dry.
Pericarp
Seed ....
Entire fruit .
IOO
IOO
IOO
9'S
40 'o
15-0
82
it
IOO
5 2
48
IOO
The relative
weights of
pericarp and
seeds in
mature fruits
before drying
begins.
Such is an example of the method that has been usually
employed, alike for the green coco-nut, weighing some sixty or
seventy thousand grains, and for the small berries and pods of
the Elder (Sambucus) and the Gorse ( Ulex\ that weigh only two
or three grains. Still, as I have before remarked, these results
are all concerned with the drying fruit. The more I handle
these " drying " data, which bulk very largely in my note-books
and have taken up a considerable portion of the time occupied
in the preparation of this work, the more my interest in them
dwindles. Nature offers to us the living fruit, and it is there
that the real biological interest lies. If she presents us also
with the dead fruit I am of course referring more particularly
to the pericarp exclusive of the seeds we ought to regard it
much as a physician would regard a patient dying from natural
decay, a process which in the fruit we should term " drying up."
I will now proceed to deal with the results of my observa-
tions on the weight-relations of the pericarp and seeds in various
types of mature fruits before any withering or loss of weight
through drying occurs. In the following table the entire fruit
is taken as 100, the proportional weight of the pericarp alone
being given, that of the seeds representing the complement.
This plan has been adopted with the object of letting the table
tell its story by the aid of a single set of figures at the same time
THE PROPORTION OF PARTS IN FRUITS 297
arranged in numerical sequence and grouped according to the
type of the fruit. If the reader desires particulars relating to
the average weight of a fruit, number of seeds, etc., he will
find them at the end of the chapter in the table containing the
elements for the determination of the drying regime of fruits.
COMPARISON OF THE WEIGHT-RELATION OF THE PERICARP IN DIFFERENT
TYPES OF FULL-GROWN FRUITS BEFORE DRYING BEGINS, THE
WEIGHT OF THE ENTIRE FRUIT BEING TAKEN AS 100.
(The fruit is here regarded as made up of pericarp and seeds. The only families
indicated are Leguminosse by L. and Palmacese by P.)
.
Relative weight of the moist pericarp,
the entire fruit being taken as 100.
Legume.
Capsule.
Berry.
Drupe.
Miscellaneous.
Pyrus Malus (Apple)
Citrus Aurantium
(a) Mandarin Orange .
(6) Common ,,
Citrus decumana (Shaddock) .
Cocos nucifera (Coco-nut)
Prunus communis (Sloe) .
Achras Sapota (Sapodilla)
Ribes Grossularia (Gooseberry)
Sambucus nigra (Elder) .
Acrocomia lasiospatha .
P.'
P.
P
89
8
85
84
99
99
98
97
95
95
93
90
89
7
86
82
75
96*
95
92
92
90
85
Arenga saccharifera
Psidium Guajava (Guava)
Momordica Charantia
Opuntia Tuna (Prickly Pear) .
Tamus communis .
Ravenala madagascariensis
Lonicera Periclymenum( Honey-
suckle)
P.
T,
5
80
75
75
Sparganium ramosum
Swietenia Mahogani( Mahogany)
Hura crepitans (Sandbox tree)
Barringtonia speciosa
Poinciana regia
Entada polystachya
Csesalpinia Sappan .
Theobroma Cacao .
L.
L.
L.
* The pericarp-proportion of 96 per cent, refers to the green coco-nut only when the
husk has attained its greatest development, whilst the albumen and shell are but partly
formed. If we imagined a fruit where the seed and pericarp reach their greatest develop-
ment together, the pericarp- proportion would be about 80 per cent. ; but nature, as
shown later on in this chapter, does not supply such fruits.
298 STUDIES IN SEEDS AND FRUITS
COMPARISON OF THE WEIGHT-RELATION OF THE PERICARP continued.
Relative weight of the moist pericarp,
the entire fruit being taken as 100.
Legume.
Capsule.
Berry.
Drupe.
Miscellaneous.
Areca Catechu (Areca-nut)
P.
74
Thespesia populnea
...
72
...
...
Ulex europseus (Gorse) .
L.
70
...
Scilla nutans ....
70
...
^Esculus Hippocastanum(Horse-
70
chestnut)
Monstera pertusa .
66
Hyophorbe Verschafftii .
P.
...
65
...
Oreodoxa regia
P.
. .
64
Csesalpinia sepiaria .
L.
64
Canavalia obtusifolia
L.
62
...
...
Mucuna urens , .
L.
61
Andira inermis
L.
61
...
Pisum sativum
L.
60
Phaseolus multiflorus
L.
60
.
...
Arum maculatum .
60
Hedera Helix (Ivy)
,
59
...
Datura Stramonium
...
58
Allium ursinum
56
.
Bignonia (near sequinoctialis) .
56
Iris Pseudacorus
...
55
...
T,
co
Faba vulgaris (Broad Bean) .
L.
jj
5
...
Guilandina bonducella
L.
5
...
Vicia sepium ....
L.
49
...
...
Artocarpus incisa (Bread-fruit)
...
49
Dioclea reflexa
L'.
47
...
Cajanus indicus
L.
47
...
...
Leucsena glauca
L.
47
.. .
...
Primula veris (Primrose) .
46
...
Mauritia setigera
P!
...
46
Acacia Farnesiana . . '.
L.
46
Aquilegia (species) .
...
...
...
...
45 (follicle)
Iris fcetidissima
43
Canna indica ....
39
Ipomcea tuba ....
35
...
...
Arenaria peploides .
...
25
...
Quercus Robur (Oak)* .
...
...
J B 35 (nut)
(C2 5
* The peculiarity in the growth of the acorn is described later on in this chapter.
Here it is sufficient to observe that A represents the pericarp-relation at the time when
the seed and the fruit-shell cease to grow together. After this the growth of the pericarp
is arrested and the seed alone increases in weight, so that the relative proportion of the
pericarp decreases, as in B and C, until the growth of the seed is in turn arrested and
the maximum weight of the fruit is attained. If in the A stage the fruit weighed 50
grains, in the B and C stages, when the shell would be hardening and losing its vitality,
the weight would be increased to 5 5 and 60 grains respectively.
THE PROPORTION OF PARTS IN FRUITS 299
This table illustrates the relative proportions of the pericarp Remarks on
, , j-1 i r i r 11 r r the table,
and the seeds in the weight or the rull-grown living rruit, or,
as we might term them, the moist relations. We should be
handling a subject bristling with difficulties if we attempted at
this stage of the inquiry to draw any inferences except such as
are of a loose general nature from these data. Yet, scanty
as they may seem, these numerical results represent a great
amount of labour, since in several cases the ground was made
secure by methodical observation of the fruit in its several
stages. For instance, some scores of the fruits of the two
species of Iris were examined, and some dozens of visits of
observation were made, in the different seasons of three
successive years, before I was satisfied with my investigation
of the fruits and could safely fix upon the full-grown moist
condition. An experience thus gained could be extended to
fruits of a similar type ; but it would be unwise to make such
an examination of the relative proportion of parts in a fruit
without some acquaintance, either direct or indirect, with the
fruit in its various stages on the plant. The more one is
acquainted with the fruit and its parts and with the different
states of its development, the more secure will be the ground
on which to base a general conclusion.
One notices that the sixty-four fruits here named princi-
pally consist of legumes, capsules, and berries, the drupes
being not so well represented. About one-sixth comprises
fruits, all of them either berries or drupes, where the weight
of the pericarp exceeds 90 per cent., or the weight of the
seeds is less than 10 per cent of the entire fruit. The
bulk of the fruits, where the seed-weight ranges from
10 to 60 per cent., and that of the pericarp from 90 to 40
per cent, of the entire fruit, is mostly made up of legumes,
capsules, and berries ; and there is not much to choose
between them in their arrangement in the scale. With
drupes and berries " size," as interpreted here by " weight,"
does not appear to count for much in determining the place
in the scale ; whilst with legumes and capsules the largest and
300
STUDIES IN SEEDS AND FRUITS
The relative
weights of
pericarp and
seeds in the
different
stages of a
fruit.
the heaviest fruits have usually the smallest seed-weight.
Thus amongst the drupes, the Sloe (Prunus communis\ weighing
about 30 grains, and the Coco-nut (Cocos nucifera]^ weighing
60,000 grains, have much the same proportions. Coming near
together amongst the baccate fruits are those of the Elder
(Sambucus nigra\ weighing 3 grains, the Gooseberry (Ribes
Grossutaria), weighing 100 grains, and the Shaddock (Citrus
decumana), weighing 14,000 grains.
Although in this respect the capsules behave mostly like
the legumes, the largest fruits having usually the greatest
proportion of pericarp, one can point to cases where fruits
widely different in size and weight have the same proportion
in their parts. Thus in the capsules of the Blue-bell (Scilla
nutans), weighing 10 grains, and in that of the Horse-chestnut
(Msculus Hippocastanum\ weighing 700 grains, the proportional
weight of the pericarp is the same. With the legumes those
fruits possessing the greatest proportion of pericarp, to wit,
those of Cassia fistula, Poinciana regia, and Entada polystachya,
are certainly the largest ; and this circumstance seems to be
associated with the presence of much ligneous tissue. In fact,
legumes like those of Pisum sativum (Pea) and of Faba vu/garis
(Broad Bean), which have a thick, fleshy pericarp, are not
conspicuously high in the scale. The same indication is
supplied in a general way by the capsules, since the two largest
and heaviest amongst them, those of Swietenia Mahogani and
Hura crepitans, are not only the most ligneous, but rank
amongst capsular fruits with the highest proportional weight
for the pericarp, namely, 85 and 84 per cent, respectively.
It should again be observed that the weights and other
particulars concerning the fruits in this table will be found in
the last table in this chapter.
The history of the proportional and absolute weights of
the pericarp and seeds of a fruit during its early growth,
maturation, and drying now demands our attention. It is a
familiar fact in the history of fruits and seeds that the pericarp
or fruit-case is as a rule in its growth far in advance of the
THE PROPORTION OF PARTS IN FRUITS 301
seed. This often comes under our notice in green leguminous
pods, as in the Pea (Pisum sattvum), where, although the pod
may be of full size, the immature seeds within are very small
and quite out of proportion to the fruit containing them,
the disproportion being subsequently removed by the rapid
growth of the seeds in the ripening pod.
The circumstance that the earlier history of a fruit's develop-
ment is mainly concerned with the fruit-case and the later
with the seed is treated with some detail in a later page of this
chapter. I will now therefore allude to that critical period in
this sequence of events which may be pronounced the turning
point in the history of the seed, that period when it has to
make the choice between entering the resting state or germinat-
ing on the plant.
There are good grounds for holding that in most fruits Both the
the seeds, which, as before remarked, are far behind the fruit- pericarp
case in the earlier stage of their growth, ultimately attain |^ t
maturity about the same time as the fruit. In order that the about the
pericarp and the seeds may reach their full development about
the same time, it is necessary that in the ripening fruit the
pericarp should considerably diminish and the seeds consider-
ably accelerate the rate of their growth. But, as indicated by Yet there are
. . f , r c - I'rr fruits where
the proportion or the parts or a fruit in different stages, as the seed con-
determined by the balance, there are evidently cases where gro^hlfter
the seed proceeds with its development after the pericarp has the pericarp
not only completed its growth but has commenced to dry. to dry.
In other words, the fruit-case begins to lose its vitality before
the seed enclosed has attained its maximum development.
This is shown in the Acorn (Quercus) and in the Coco-nut,
and, as my observations suggest, probably in the fruits of
Barringtonia speciosa. It would thus promise to be not in-
frequent with one-seeded fruits of these types.
Before giving the data on which these general inferences
are based, I should remark that this subject only came into
prominence during the elaboration of my data. It was the
comparison of the results obtained for coco-nuts and acorns
3 02 STUDIES IN SEEDS AND FRUITS
that first opened my eyes to its importance. Although I can
only claim to have broken the ground, the contents of the
following table ought to be of interest. If figures can tell a
story, these data plainly show the varying rates of growth of
the pericarp and the seeds in the development of the fruit,
besides illustrating their history in the drying stage when the
pericarp has ceased to grow and begins to die. From this
standpoint we have two types of fruits displayed in the table.
The first, which is probably by far the commonest, is repre-
sented by the capsules of Iris and ALsculus and by the legumes
of Faba, Phaseolus, and Entada. Here the time of the
maximum growth of the seed roughly corresponds with that of
the pericarp, the seed entering upon its rest-period when the
fruit-covering begins to dry and lose weight. The second
is represented by such closed fruits as the acorn or nut of
the Oak (Quercus Robur\ and by the berry of Earringtonia
speciosa and the drupe of the Coco-nut Palm, the two last
possessing husky pericarps. Here the seed continues to add
to its weight and size after the pericarp has ceased to grow
and has begun to dry.
The point in the case of the fruit of Barringtonia^ however,
needs further investigation ; but the indications are very
suggestive. Thus, in the table given below it is shown that
the drying fruit, weighing 4000 grains, has a heavier seed
than the full-sized moist fruit, weighing 9000 grains, that has
not yet begun to dry. The same thing is brought out in the
table illustrating the history of the fruit of Earringtonia speciosa
given in Note 1 1 of the Appendix. It will be found there
remarked under J that the seed has probably increased its
weight whilst the husk has been drying.
It is quite possible that future investigators will discover
that the differences between the two types of fruits represented
in the following table are more in degree than in kind, and
that even in the prevailing type the seeds may continue to
add to their weight for a little while after the fruit -case has
begun to lose its vitality and to dry. There are distinct
THE PROPORTION OF PARTS IN FRUITS 303
TABLE SHOWING THE PROPORTIONS BY WEIGHT OF THE PERICARP AND SEEDS
DURING THE DIFFERENT STAGES OF FRUITS, INCLUDING THE IMMATURE,
MATURE, AND DRIED CONDITIONS.
(The weights are in grains. In the percentage columns the entire fruit is taken as 100.)
Plant-name.
Parts.
Green fruits with
immature seeds.
Ripe fruits with mature seeds.
Less than
half size.
More than
half size.
Full size
before
drying.
Early drying
stage.
Drying
in air
completed.
*J
|
i
J
SP
n>
o
c
B
Put
A
M
'53
iJ
1
u
g
u
(X
|
'1
'J
If
1
M
I
V
V
u
JJ
PH
.5?
'53
V
W
a
C
V
u
c
1
Iris fcetidissimal
(capsule) 1
Pericarp
Seeds
Entire fruit
...
...
73
67
140
52
48
IOO
78
IO2
I 80
43
57
IOO
25
75
IOO
25
75
IOO
IS
30
45
34
66
IOO
Iris Pseudacorus \
(capsule) j
Pericarp
Seeds
Entire fruit
77
23
100
77
23
IOO
98
42
140
70
30
IOO
35
"5
250
54
46
IOO
86
94
1 80
48
52
IOO
16
49
65
25
75
IOO
^Esculus Hippo- (
castanum (cap- !
sule, i -seeded) (
Pericarp
Seeds
Entire fruit
2l8
42
260
84
16
IOO
468
132
600
78
22
IOO
49
210
700
70
30
IOO
400
200
600
66
34
IOO
68
IOO
168
40
60
IOO
Entada polysta- I
chya (legume) |
Pericarp
Seeds
Entire fruit
425
75
500
85
15
IOO
600
200
SOO
75
2 5
IOO
...
149
9 1
240
62
38
IOO
Faba vulgaris(5- I
seeded legume) |
Pericarp
Seeds
Entire fruit
170
30
200
85
15
IOO
455
245
700
65
35
IOO
400
4OO
800
5
5
IOO
240
360
600
40
60
IOO
48
152
200
24
76
IOO
Barringtoniaspe- (
ciosa (baccate,-!
r -seeded) \
Pericarp
Seeds
Entire fruit
1980
20
2000
99
i
IOO
4800
200
5OOO
96
4
IOO
7380
l620
9OOO
82
iS
IOO
1880
2120
4OOO
47
53
IOO
7 02
648
I3SO
52
48
IOO
Cocos nucifera, (
Coco - nut-*
(drupaceous) (
Pericarp
Seeds
Entire fruit
9,900
I, IOO
1 1,OOO
90
10
IOO
57,600
2,400
6o,OOO
96
4
IOO
19,000
7,400
26,400
72
28
IOO
14,040
3,960
l8,OOO
78
22
IOO
: Quercus Robur, I
Oak (nut) 1
Pericarp
Seeds
Entire fruit
'3
7
20
65
35
IOO
18
4
32
57
43
IOO
2O
26
4 6
44
56
IOO
17
40
57
30
70
IOO
5
21
26
1 9
81
IOO
Phaseolus multi- f
florus, Scarlet- I
runner (4 - j
seeded legume) \_
Pericarp
Seeds
Entire fruit
133
7
140
95
5
ICO
200
5
250
80
20
IOO
1 80
1 2O
3OO
60
40
IOO
no
9
200
55
45
IOO
27
4 8
75
36
64
IOO
Note. Although in selecting the fruits to form the same series those similar in character were
hosen, minor inconsistencies occur, but the general trend of the data is to be relied on.
304 STUDIES IN SEEDS AND FRUITS
indications of this in the data given for Faba vulgaris and
Phaseolus multiflorus.
In order to throw light on this matter, as concerning the
coco-nut, I will give some of the results of observations made
in Jamaica. Though the data tabulated below do not present
a continuous record, the intervals can be readily filled up ;
and it may be added that the general trend of results illustrated
in these tables is confirmed by indications supplied by a
number of other fruits in addition to those for which the
record is here given.
It will be seen from the tables that the drying of the
full-grown green fruit is practically the drying of the husk
alone, since it is likely that mould and other causes of decay
usually come into play in nature before the completely air-
dry condition is attained, as exemplified in column D. Indeed,
planters hold that fruits kept too long do not usually dry
up, but rot and decay. Whilst the drying of the husk is
proceeding on the plant, remarkable changes take place in the
shell and in the kernel. In a full-grown green fruit, as is
well known, the shell is thin and the kernel soft and almost
creamy. During the drying process the maturation of the
seed proceeds. Whilst the husk is losing pounds in weight,
the shell is becoming tougher and thicker, and the kernel
solidifies and increases in quantity. But the increase of the
kernel is much greater. Though in the green fruit its weight
is rather less than that of the shell, it becomes 50 per cent,
heavier as the seed ripens in the drying fruit. When, how-
ever, after many months of drying, the fruit has yielded all its
water to the air, except the water of hygroscopicity, which,
according to the principle laid down in Chapter VII., is
common to both living and dead vegetable matter, the weight
of the kernel is only about the same as that of the shell.
Such a completely air-dried condition, as has been observed
above, would be rarely attained in nature. This last stage
is more fully discussed in the explanatory remarks that follow
the tables.
THE PROPORTION OF PARTS IN FRUITS 305
TABLES SHOWING THE RELATION OF PARTS BY WEIGHT IN DIFFERENT
STAGES OF THE COCO-NUT (Cocos NUCIFERA). (Table I. is in
grains; Table II. in grammes.)
I. GRAINS.
(Data obtained from individual nuts in different stages.)
A.
B.
C.
D.
Full-grown
green fruit.
Fruit in the
early stage
of drying on
the tree.
Fruit after dry-
ing for 2 to 3
months on tree
(a ripe fruit. )
Fruit completely
air-dried (see
explanation of
tables).
Parts.
Weight.
Per-
centage
of entire
fruit.
Weight.
Per-
centage
of entire
fruit.
Weight.
Per-
centage
of en tire
fruit.
Weight.
Per-
centage
of entire
fruit.
Husk .
Shell .
Kernel
Water .
4 6 75
2,640
2,200
3.410
85-0
4'8
4-0
6-2
31,185
2,618
3,080
1,617
8i'o
6'8
8-0
4-2
I3.440
3.744
5,952
864
56'
15-6
24-8
3-6
9410
3480
357
57'2
Zl'I
217
Total .
55,000
lOO'O
38,50
lOO'O
24,000
lOO'O
16,460
lOO'O
Relation of the
total weights
IOO
70
44
30
II. GRAMMES.
(The proportions given in Table I are here applied to a fruit assumed to weigh origin-
ally 4000 grammes, or nearly 9 Ibs. )
Husk .
3400
85-0
2268
8i'o
986
56*0
686
57-2
Shell .
192
4-8
190
6-8
275
15-6
254
21 'I
Kernel
1 60
4-0
224
8-0
436
24-8
260
21'7
Water .
248
6-2
1x8
4-2
63
3-6
Total .
4000
lOO'O
2800
lOO'O
1760
lOO'O
1 200
lOO'O
Relation of the
IOO
7
44
30
total weights
20
3 o6 STUDIES IN SEEDS AND FRUITS
Explanation Though these tables largely explain themselves, a few
of die tables. eX pi ana t O ry remarks are necessary. The data in Table I
were obtained from individual fruits, excepting those in column
D, those fruits being selected which came from the same palm
and gave results similar to those supplied by others in the
same stage. In Table II the percentages shown in Table I
are applied to a green, full-sized fruit of average weight. It
is important to notice that whilst the first table is in grains,
the second is in grammes. All the observations were made
during the winter 1907-8 in Jamaica.
The contents of column D call for special remark. They
represent the results of different experiments on the ordinary
The com- drying in air of the separate husk, shell, and kernel, applied
<iriedcoc to tne fruit m tne stage at which they reach their greatest
nut development. Since the husk attains it in the green unripe
fruit of full size, the drying experiment was made on the
husk at this stage. In the same way and for the same reason
the shell and kernel of the ripe fruit were subjected to the
drying test. The following results were obtained :
Loss of weight when dried in air of husk of green coco-nut,
80 per cent.
Loss of weight when dried in air of shell of ripe coco -nut,
7 per cent.
Loss of weight when dried in air of kernel of ripe coco-nut,
40 per cent.
To produce the completely air-dried coco-nut these losses
had to be applied to the husk of the green fruit in column A,
and to the shell and kernel of the ripe fruit in column C.
The fruit typified in column D is therefore a coco-nut that
has given up all its water to the air, or rather all the water
that the air can absorb, the fruit retaining only what it would
hold independent of its vitality. This completely air-dried
fruit represents, accordingly, rather the result of a laboratory
experiment than a process of nature, since, as previously
remarked, we should only expect to find a coco-nut in this
state under exceptional conditions. Such a fruit would most
THE PROPORTION OF PARTS IN FRUITS 307
probably have lost its germinative capacity, as may be inferred
from my observations on the embryo of the coco-nut recorded
in Chapter XVIII. But although these data are concerned
with a dead fruit, they bring the completely air-dried fruit
of the Coco-palm into line with other fruits in the same
devitalised condition, such fruits only holding the water of
hygroscopicity which is common to both living and dead
organised vegetable matter. If we were asked what stage
in the drying of a coco-nut corresponds to that of the dried-
up apple, cherry, and currant as they hang in dry weather
from the tree, we should point to the completely air-dried
fruit of column D. The trade husked coco-nut, such as
is sold in the English markets, would be drier than the ripe
fruit of column C, but moister that that of column D. If
kept under dry atmospheric conditions and secured against
the attacks of mould, it would lose more water.
It would thus appear that what the planter calls a "ripe" A "ripe"
coco-nut is a fruit that has lost in the ripening process rather
over half its weight as a green nut. This process may be
completed on the tree, or it may be continued in the stored,
detached fruit which has been gathered in the early ripe
condition. When we speak of the fruit as maturing its seed
whilst it dries on the palm, we are not adopting the phraseology
of the planter. For him a ripe nut is a fruit with a thick, solid,
oily kernel ; and in practice he is less concerned with the mode
of ripening than with the characters indicating his ripe fruit.
Thus, the statement in Simmond's Tropical Agriculture that
the seed-nut must be "fully ripe and not aged" would be
full of meaning to the planter, but it might be misinterpreted
by one not familiar with the Coco-palm in its home.
However, the theoretical view advanced above that the The seed of
seed grows whilst the fruit is drying is in accord with practical grows whilst
experience. Ripe nuts, it is advised in the work above named, *s drying-'" 1 '
should be allowed to dry for not less than a month after
gathering before they are planted. If intended for " copra "
they should not be broken up for four or six weeks after
3 o8 STUDIES IN SEEDS AND FRUITS
gathering. This implies that the maturation of the seed is
continued after the early ripe fruit has been detached. It is
during the period of storage, covering usually one or two
months, that the oil in the kernel increases considerably in
amount. The proportions of water and oil in the kernel vary
Decrease of in an inverse relation, the water gradually diminishing and the
the water -i j 11 .1 r T
and increase oil gradually increasing as the rruit matures. In an interesting
of the oil. compilation entitled All about the Coco-nut Palm, which was
published at Colombo in 1885, the following are given as the
proportions of water and oil in the kernels of young and
ripe fruits as obtained by M. Lepine of Pondicherry :
Young coco-nuts contained 90-3 per cent, of water and 2-3 per
cent, of oil.
Ripe coco-nuts contained 53-0 per cent, of water and 30-0 per
cent, of oil.
This increase of the oil in a stored coco-nut is a point
emphasised by different writers in the book just quoted ;
and it is one on which stress is laid in a letter to me by
Mr H. Matthes, a planter of " Bacolet," Tobago.
The use of the term " young " deserves a word of explan-
ation. It is applied to the full-sized green fruit with shell
and kernel but partially formed. The term " ripe " is applied
to a fruit with a hard shell and a thick solid kernel. During
the ripening process the husk loses a large amount of water,
and in consequence the ripe fruit is much lighter in weight
than the green fruit, though to the inexperienced eye its
appearance may not be greatly changed.
As confirming my method, I have compared below the
proportions of parts for young and ripe fruits as given in
All about the Coco-nut Palm with my own results. The data
Observations are apparently all derived from M. Lepine, but they are
of Lepine. , ./, n . r .u
concerned with a smaller variety or coco-nut than that experi-
mented upon by me in Jamaica. Since the husk and shell are
not distinguished by him in the young nut, I have followed
the same plan in the subjoined table.
THE PROPORTION OF PARTS IN FRUITS 309
COMPARISON OF THE PROPORTIONS OF PARTS IN COCO-NUTS AS
OBTAINED BY LUPINE AND GUPPY.
Young fruit (Lepine).
Ripe fruit (Lepine).
Percentages obtained
by Guppy.
Weight in
grammes.
Percentage
of entire
fruit.
Weight in
grammes.
Percentage
of entire
fruit.
Green.
Ripe.
Husk and shell
Kernel .
Water .
1760
90
300
81-9
4 "
13-9
766
434
250
53'
3o'o
17-0
89-8
4-0
6'2
71-6
24-8
3'6
Total .
2150
lOO'O
1450
lOO'O
lOO'O
lOO'O
A.
B.
C.
D.
E.
F.
After allowing for variation in the proportion of parts in
coco-nuts of different localities, it is easy to recognise in the
young and ripe fruits of Lepine the green and ripe fruits of
my tables. In both sets there is a marked increase in the
absolute weight and in the relative amount of the kernel in
the green (young) and ripe fruits. M. Lepine's fruits were
evidently selected at random ; but it is to be noted that his
young fruit is about 50 per cent, heavier than his ripe fruit.
The question cannot be further discussed here, but it should be
added that the total amount of water in the coco-nut is dealt
with in Note 27 of the Appendix, and that the subject of the
embryo is treated in Chapter XVIII.
As another example of those cases where the seed continues The case of
to increase in size and weight after the pericarp has ceased to (Q^ercus"
grow and is beginning to lose its vitality, I will take the fruit Robur )-
of the Oak (Quercus Robur}. Here the subject is bound up
with that of the occasional vivipary of the acorn, or, in other
words, with its germination on the tree, a matter dealt with in
Chapter XIX. My observations were made at Salcombe in
Devonshire in the successive autumns of 19081911. The
3 io STUDIES IN SEEDS AND FRUITS
method employed consisted in making observations system-
atically during the five or six weeks preceding the fall of the
acorn from its cupule in October. On each occasion a number
of fruits were gathered from the same two or three trees, and
ten were selected for examination and experiment. The vital
connection with the parent plant is maintained by the attach-
ment of the base of the fruit to its cupule. When the acorn
begins to " brown " this attachment to the cupule begins to
loosen, the result evidently of the drying of the pericarp or
shell. The " browning " and drying of the shell proceed until
the biological union with the cupule is severed, when at a
touch the acorn falls to the ground.
Explanation With regard to the table on opposite page it may be observed
>f the tab e. ^^ ^ e acorns o f th e experiment in 1 908 were larger and heavier
than those employed in 1910, a difference that will explain the
divergencies in the absolute weights. The results of many
observations are embodied and stated numerically ; but there
is much that of necessity finds no expression in the figures.
A careful examination is needed before the data here tabulated
can be used legitimately, and especially is it requisite that
those making use of them should know a little of the acorn
and its ways. As far as is consistent with its being a tabular
statement, the author has endeavoured to make it as self-
explanatory as possible. But he can hardly expect his readers,
whilst perusing the dry array of numerical results, to invest
them with the interest they created in his mind as they
gradually disclosed their story in the course of a fascinating
piece of investigation. That interest they can only acquire by
going to the Oak themselves and by appealing to the balance
in an inquiry that should at least cover two seasons. The secret
of vivipary will lie behind the results of their observations.
To show how this table is to be employed I will take one
of the entries, that of September 27, 1910. It is here indicated
that in a freshly gathered acorn, weighing 50 grains, the shell
or pericarp weighed 1 9 and the seed 3 1 grains. In other
words, as stated in the next two columns, taking the weight of
THE PROPORTION OF PARTS IN FRUITS 311
TABLE ILLUSTRATING THE GROWTH OF THE ACORN (QUERCUS ROBUR)
AS REVEALED BY THE BALANCE, DURING THE SIX WEEKS PRECEDING
ITS DETACHMENT FROM THE CUPULE, FROM OBSERVATIONS MADE
BY THE AUTHOR AT SALCOMBE, DEVONSHIRE, IN 1908 AND 1910.
(The cupule is not included in these observations.)
Relative
Loss of weight
Average weight
weight of
after drying in air
Date
Condition and state of
in grains of a
the pericarp
at the ordinary
when
attachment of the fruit to
single fruit and
and seed,
temperature, stated
gathered.
the cupule.
its parts (10 nuts
taking the
as a percentage of
in each case).
entire fruit
the weight in the
as loo.
moist fruit.
1910.
Total.
Peri-
carp.
Seed.
Peri-
carp.
Seed.
Entire
fruit.
Peri-
carp.
Seed.
f Firmly attached by liv-
,
Sept. 13
\ ing tissue to the
(3 2
18-2
13-8
57
43
74 -o
76*0
70 'o
2
1 cupule ; pericarp 2
(46
21-6
24-4
47
53
72-0
76-4
67-8
( mm. thick and moist
j
>, 27
/ Attachment looser ; be-
ISO
19*0
31-0
38
62
64-4
72-8
59-2
Oct. 4
\ ginning to turn brown
\S5
19-3
357
35
65
6i'o
68-7
56-8
"
Easily detached, but still
5 1
'5'3
357
3
70
47 '4
62-6
41 'o
a slight biological
connection ; brown-
ing pericarp thinner
and drier
18
Falls at a touch from the
57
17-1
39'9
30
70
477
57'5
43'5
cupule ; well browned
'8
After keeping for some
26
...
*9
81
...
time and no longer
losing weight, pericarp
very thin, 0*3 mm.
1908.
Sept. 4
7
( Firmly attached to
t cupule ; pericarp
thick and moist
J56
r
24*6
29-1
u> u>
(J H
SO *>*
44
47
56
53
25-0
32-3
3
Oct. 6
i Attachment loosening ;
browning ; pericarp
thinner and drier
u,
J 71
45'5
48-6
...
18-1
S2-9
25'5
74'5
"Vital connection
64
57 "4
> X 4
severed ; falls at a
v *r
touch from the cupule
51 H
After keeping for some
35
18
82
...
months and no longer
losing weight
the fresh fruit as 100, the shell makes up 38 and the seed 62
parts of the whole. When this fresh acorn is allowed to dry
in ordinary air, until it ceases to lose weight and exhibits
merely the usual hygroscopic variations regulated by the
3 i2 STUDIES IN SEEDS AND FRUITS
atmospheric humidity, the shell or pericarp loses 72*8 per cent,
of its moist weight, the seed 59-2 per cent, and the fruit in its
entirety 64*4 per cent. Such are the indications given in the
columns of this table for the acorn gathered at this date.
When we compare them with those fruits collected earlier and
later, we find that during the acorn's growth the seed steadily
increases its weight and decreases its water-contents long after
the pericarp has ceased to grow and has begun to dry.
This table will be noticed in different connections, but
especially in relation to vivipary or germination on the
plant in Chapter XIX. With these explanatory remarks
I will now proceed to refer more in detail to the particular
lesson which the data furnish us here respecting the develop-
ment of the acorn on the tree, namely, the continued growth
of the seed after the fruit-shell has begun to lose its vitality.
This is not only the tale of the balance ; but it is the story that
the acorn, as we handle it, conveys to us plainly enough in the
increase in size, weight, and solidity of the seed, whilst the
shell is becoming thinner and drier in the " browning " process.
The tendency of a seed in some cases to continue its growth
after the fruit-case or pericarp has begun to lose weight and
dry, in other words, to die, finds its final expression in the
germination of the seed on the plant. To put it in another
way, it is a step towards vivipary. It is not by a mere coin-
cidence that I am enabled to bring into touch with the
viviparous habit all the three plants that have before been
mentioned as illustrating the normal growth of the seed after
the pericarp has begun to dry and to lose its vitality. In the
cases of the Oak and the Coco-nut Palm, the connection is
more or less direct, whilst with Barringtonia speciosa the implica-
tion is only indirect.
Theconnec- Thus in Chapter XIX I have dwelt upon the tendency to
vivipary displayed by the nuts of the Oak (Quercus Robur\
as observed by me during successive years at Salcombe in
seed after the Devonshire. That the coco-nut does occasionally "sprout"
fruit-case has . . , . .. ' . ,
begun to dry. on the palm came under my notice in tiji (Plant Dispersal, by
THE PROPORTION OF PARTS IN FRUITS 313
H. B. Guppy, p. 472) ; and there is to be cited in this
connection the well-known habit in the Pacific of suspending
the ripe fruits from a tree by a strip of the husk and leaving
them exposed to the weather until they germinate. Although
there is no evidence of vivipary in the case of the fruits of
Earringtonia speciosa, there are grounds for believing that the
fruits of an allied species (B. racemosa\ which are frequently
found germinating in the floating drift of the Rewa estuary
in Fiji, begin to germinate whilst hanging from the trees that
abound at the water-side (ibid.) pp. 564, 575).
The discovery of this peculiarity in the growth of the Thedis-
acorn was made in this way. My attention was first directed the seed of*
to some anomaly in the growth by an impossible result the acorn
produced by applying: a shrinking; ratio deduced from experi- growth after
i J i r r 1 1 j i_ i the shell has
ments on the drying or moist rull-sized nuts gathered in the begun to dry.
middle of September, 1908, to fruits of the same tree well
dried after being kept some months. Since the moist fruits
in question lost just two-thirds of their weight whilst drying,
and since the dry acorns, gathered when ready to fall from
the cupule, now weighed from 30 to 40 grains in each case, it
followed from the application of the shrinking ratio that their
original weight as moist fruits must have been between 90
and 1 20 grains. As a matter of fact, from the tree concerned
I had rarely obtained moist nuts more than half this weight.
Influenced also by other considerations, 1 made a note at the
time that " it is not at present possible to obtain a satisfactory
shrinking ratio for the moist green acorn, since the kernel
apparently adds to its weight after the shell has ceased to grow
and has begun to dry."
Strangely enough, although I had noticed on this and
neighbouring trees that whilst the acorns were still attached to
the cupule on the tree their seeds were in some cases splitting
their shells and in rare instances actually protruding the radicle,
the connection between the anomaly above described and the
vivipary did not then present itself. So the matter rested for
.a year and more, until, having found that a similar anomaly in
This peculi-
arity in
growth re-
presents the
first step
towards
vivipary.
The drying
of the shell
in the ripen-
ing acorn.
STUDIES IN SEEDS AND FRUITS
the shrinkage of the coco-nut was satisfactorily explained by
the growth of its seed after the husk had begun to dry, I
began to examine in this light my data for the acorns of the
autumn of 1908. The growth of the kernel after the shell
had begun to lose weight and dry was unmistakably brought
out in the results of my weighings, as is shown in the table.
Further observation on the tendency to germination of the
acorn on the tree was made in the autumn of 1909 ; and
during September and October 1910 systematic weekly
observations and experiments were carried out on neighbouring
trees, leaving the original tree for the study of the viviparous
tendency. The results told the same story ; and their
indications were emphasised by those of fresh experiments on
the water-contents. It thus finally appeared that the tendency
of the seed of the ripening acorn to increase in weight after
the pericarp or shell has begun to dry finds its final expression
in the splitting of the shell and in the germination of the seed,
whilst the fruit is still attached to the cupule on the tree. It
was the first step towards vivipary, and a sign diagnostic of
the potentially viviparous habit of the oaks observed. Such is
the history of my researches in this connection.
It is noteworthy that the observations made in 1908 are
in one respect more significant than those of 1910 in showing
how the seed of the acorn continues its growth after the shell
or pericarp has begun to lose its vitality and to dry, since
they were carried out with no special view in my mind.
But it is to the more systematic observations of 1910 that
I will now more especially refer, since the data there enable
us to compute the water-contents as far as they are shown
by the loss of weight of the materials when dried under
ordinary air-conditions. During the period between the
middle of September and the middle of October, the weight
of the seed increased from about 14 to 40 grains, whilst its
water-percentage decreased from about 70 to 40 per cent.,
thus indicating a very marked addition to the solids as it
grew. But there was no such continuous growth of the shell
THE PROPORTION OF PARTS IN FRUITS 315
or pericarp during this period ; and, as in the case of the
seed, the two sets of observations for 1908 and 1910 tell a
similar story. In the third week of September, when the
shell had reached the height of its growth, it was moist,
almost fleshy inside, and about 2 millimetres thick. After
this it began to turn brown, lose weight, and to dry, signs
of the severance of its vital connections that antedated those
of the seed. Whilst the seed had been getting larger, heavier,
and more solid, its shell had been getting thinner and drier,
so that when the acorn was ready to fall from its cupule,
its well-browned shell had lost more than half its original
thickness and much of its water. Such are some of the
changes in relation between the seed and shell of the acorn
illustrated in the table. They are still more evident when
we handle the ripening acorns on the tree.
On looking at the general table given on p. 303 showing The general
the proportions by weight of the pericarp and seeds during lu^theVruit*
the early growth, maturation, and subsequent drying of a ^^' s and
variety of fruits, it will be noticed that as a general rule from dries, thei
, f 11-1- i i proportion oi
the young rruit on the plant with immature seeds, to the the pericarp
withered-up fruit, as it lies on the ground, there is a con- an^that^f
tinuous decrease in the proportion by weight of the pericarp, !^ e seeds
r . t i increases,
and a continuous increase in that of the seeds. In some
fruits, it is true, as in the capsule of Iris fcetidissima and in
the fruit of the Coco-palm, the proportional amount of the
pericarp in the completely dried fruit is rather more than in
the earlier drying stage, a result due to the seeds losing weight
less readily at first, as explained below. But this does not
seriously affect the general trend of the figures ; and it is
very probable that in the majority of fruits of the type of
the capsule and the legume the general decrease in the pro-
portional weight of the pericarp, as the fruit grows, matures
and dries, would not exhibit any such interruption.
It is a familiar fact of observation that the earlier history illustrations
of a fruit's development is mainly concerned with the fruit- principle,
case and the later history with the seed. Nothing short of
Phaseolus
multiflorus
and Faba
vulgaris.
Iris Pseuda-
corus.
31 6 STUDIES IN SEEDS AND FRUITS
handling and actual inspection can be more effectual than the
data in this table in bringing out the fact that the growth of
the fruit-case is for a long time far in advance of that of the
seed. As typical of the behaviour of legumes I will take
the pods of the Scarlet-runner (Phaseolus multiflorus] and the
Broad Bean (Faba vulgaris\ and as representing the capsules
the fruit of Iris Pseudacorus.
In the young pods of the Scarlet-runner and of the Broad
Bean, when less than half the mature size, the contrast between
the large fruit-case and the diminutive, partially formed seeds
is very striking. On the average the weight of the fruit-case
would be about 90 per cent, of the total weight of the entire
fruit. When the pods have attained maturity in the moist
condition, the proportion is lowered to 50 or 60 per cent. ;
and in the air -dried pods it is still further reduced to 25
or 35 per cent. From an early stage in the fruit's develop-
ment until it hangs as a dried-up pod on the plant there is
a continual decrease in the proportional weight of the pericarp
or fruit-case. Up to the time of maturity this decrease is
due to the active growth of the seeds. After maturity it
arises from the larger water- contents and the consequently
greater drying capacity of the fruit-case.
The capsules of Iris Pseudacorus give similar indications.
Here also we notice in the columns of the table that there
is a continuous decrease in the relative weight of the pericarp.
When the young fruit is only two-fifths of the mature size,
the proportion is as much as 77 per cent. ; and it attains the
minimum of 25 per cent, in the completely air-dried fruit.
If we had commenced with a still younger fruit, the proportion
of pericarp would have been as much as 85 or 90 per cent.
But it is obvious that this continuous decrease is brought
about by different causes during the growing and the drying
stages. In the early growing stage, when the seeds are small
and their contents more or less unformed, the pericarp greatly
predominates ; but as growth proceeds and the ripening stage
is approached, the seeds rapidly add to their weight, and the
THE PROPORTION OF PARTS IN FRUITS 317
proportion of the pericarp decreases up to the time of maturity.
The subsequent decrease in the drying stage is due to the peri-
carp holding relatively more water than the seeds, and to its
giving it up to the air more readily. It will be noticed in the
table on p. 303 that when allowed to dry in the air, the pericarp
of the moist mature fruit reduces its weight from 135 to 16
grains, a loss of as much as 88 per cent, of its weight, whilst in
the full-grown soft seeds of the ripe fruit there is a reduction
in weight from 115 to 49 grains, a loss of about 57 per cent.
We may here cite the case of the acorn, which acts quite The acorn.
in accordance with the principle that the proportional weight
of the fruit-case is a continually decreasing quantity as the
fruit develops, ripens, and dries. As high as 65 per cent.
in an immature fruit only one-third of the mature size, the
relative weight of the shell or pericarp is reduced rapidly,
being 44 per cent, when the seed has attained its maximum
size and weight in the moist condition, and as little as 19
per cent, in the air-dried acorn lying on the ground. These
results are those given in the general table on p. 303.
It will be observed in the same table that a small divergence Small de-
in behaviour is displayed by the fruit of Iris fcetidissima in the
drying stage ; and we notice it also in the fruits of Barringtonia
steciosa and Cocos nucifera (Coco-nuO. Here during the drying: sima Cocos
\ 1 j i -111 nucifera, and
process, as previously remarked, there is a period when the Barringtonia
loss in weight of the seed is checked and the loss in that s P eclosa -
of the pericarp proceeds very rapidly. In time, however,
the seeds, like the pericarp, surrender their water to the air ;
and the temporary check is indicated by the circumstance
that the lowest proportional weight of the pericarp is found,
not in the completely dried state, as in Iris Pseudacorus and in
Msculus Hippocastanum (Horse-chestnut), but in the earlier
stage of the drying process. The cause of this check to the
drying of the seeds arises in Iris fcetidissima from the amount
of saccharine material in the seed-coverings, and in Barringtonia
speciosa and Cocos nucifera from the hindrance imposed on the
seed-drying by the enveloping pericarp. The history of the
3 i8 STUDIES IN SEEDS AND FRUITS
pericarp relation in the husky fruit of Barringtonia speciosa is
especially instructive. Here, as shown in the table in Note
1 1 of the Appendix, the pericarp proportion remains as high
as 98 or 99 per cent, until the fruit has attained to one-third
of the full size. When the fruit is half size, it is still as
much as 96 per cent., and after this falls to 82 per cent, in
the full-grown fruit, and to about 50 per cent, when the
fruit is lying completely dry on the ground.
Thesignifi- Much significance lies in the circumstance that as the fruit
dries on the plant the seeds form a larger proportion of the
weight of the entire fruit. When the moist fruit dries the peri-
e pen- o
carp loses carp loses far more water than the seed, the result being that
water than whilst the fruit-case dies the seed lives. If we were to strike
the seed. a j-^gh average from the data given in the table on p. 320, and
more particularly from the results summarised for types at its
end, we would say that whilst seeds as a rule lose half their
weight during the drying process on the plant before entering the
rest-period, the pericarp loses generally from 70 to 85 per cent.
And it is in It is, however, in the behaviour of the pericarp that fruits
of the peri- differ most, the seeds as a rule presenting much less contrast
fm^dfffer * n ^ s respect. Taking the averages below given, we find
most. that the pericarp sustains the greatest loss of 86 or 87 per
cent, in the case of typical fleshy or pulpy berries and typical
moist capsules, the living capsule being essentially a more or
less fleshy and watery fruit. The significance of this close
similarity in behaviour has been already dealt with in Chapter
XII ; but it is of interest here to note again that ripe fruits
seemingly so contrasted as those of the Apple, Gooseberry,
(Ribes), Prickly Pear (Opunfia), on the one hand, and those
of Canna, Datura, Ipomcea, and Iris on the other, yield up
much the same amount of water as the fruit-case dries naturally
on the plant. Next come fleshy drupes, typically represented
by those of Prunus communis, which experience a loss of 75
per cent. Then we have the legumes with an average loss
of weight of 72 or 73 per cent. ; and last come the large woody
capsules, exemplified by those of the Mahogany tree, Ravena/a,
THE PROPORTION OF PARTS IN FRUITS 319
and Hura crepitans^ where the average loss is rather over
60 per cent.
It is remarkable that when grouped on the basis of the
loss of weight sustained by the pericarp during the drying
process on the plant the fruit-types arrange themselves in a
regular series, commencing with typical berries and capsules
and ending with woody capsules and Palm fruits. This is
shown in the following results which are taken from the
summary at the end of the subjoined table.
Loss sustained by fleshy capsules and pulpy berries 86 or 87 per cent.
fleshy drupes 75
legumes 73
woody capsules 63
Palm fruits 62
Seeds, as already remarked, are much more constant in
behaviour. As indicated in the summary of the results of
the table, if we exclude Palm seeds, they lose on the average
about half of their weight, the seed proper of the Palm losing
as a rule about a third of its weight.
The drupaceous and baccate fruits of Palmaceae are often
considerably affected by the presence of oil or of sugars in the
pericarp. Thus, whilst the pericarp of the fruit of Cocos
nucifera (Coco-nut) contains an abundance of water and loses
about 79 per cent, of its weight in the drying, that of Cocos
plumosa, which holds a large amount of sugar, loses only
37 per cent. So, again, with the fruits of Areca Catechu^ the
fruit-case experiences a loss of 77 per cent, of its weight ;
whilst the pericarp of those of Qreodoxa regia, which holds much
oil, loses only 42 per cent.
If space permitted it the treatment of this subject might be
greatly extended ; but many points are dealt with in different
parts of this work, and the elements for determining the dry-
ing regime of many fruits and seeds not specially discussed
here will be found in the table at the end of this chapter.
Numerous matters of lesser interest cropped up in this part of
my inquiry ; but it would be scarcely worth while, even if there
320
STUDIES IN SEEDS AND FRUITS
was no other reason against it, to burden these pages with
recounting them. One which occurs to me as I write is the
relations as regards weight and size between the placental axis
or columella of certain capsules. In Note 17 of the Appendix
I compare together in this respect the capsules of the Primrose,
weighing about 4 grains, and of the Mahogany tree, weighing
about 6000 grains, or 1 500 times as much. Although this is
a comparison of the small with the great, the balance is equally
effective in both cases in determining the relation of parts.
THE PERICARP AND THE SEED.
TABLE COMPARING THEIR Loss IN WEIGHT DURING THE DRYING
AND SHRINKING PROCESS.
(The results are given in percentages, the moist pericarp and the soft, uncontracted
seed of the ripe fruit being taken as 100. The data have been selected with the object
of contrasting the behaviour of different types of fruits. They are all to be obtained by
constructing the drying regime for each fruit from the elements given in the last table
of this chapter ; but the shrinkage of the seeds is also given in Chapter IX.)
Plant-name.
Type of
fruit.
Loss in weight during
the drying process, the
moist condition being
taken as 100, the dry
weight being then given.
Pericarp.
Seed.
Arum maculatum ....
Lonicera Periclymenum (Honeysuckle)
Opunti.i Tuna ( Prickly Pear)
Pyrus Malus (Apple)
Berry
100 15
100 19
100 14
100 14
100 13
IOO IO
ioo 61
ioo 60
ioo 49
ioo 51
ioo 60
ioo 64
Ribes Grossularia (Gooseberry) .
Tamus communis ....
M
>j
Prunus communis (Sloe) ....
Drupe
100 15
ioo 53
^Esculus Hippocastanum (Horse-chestnut)
Allium ursinum .....
Canna indica ......
Capsule
}
IOO 14
zoo 17
ioo 13
IOO II
ioo 14
ioo 1 6
ioo 1 6
ioo 7
ioo 48
ioo 55
ioo 68
ioo 63
ioo 31
ioo 36
ioo 42
ioo 67
Ipomcea tuba
Iris fcetidissima ) (
Pse U dacoru S } meanresult ' |
Primula veris (Primrose) ....
Scilla nutans (Bluebell) ....
THE PROPORTION OF PARTS IN FRUITS 321
PERICARP AND SEED. TABLE OF Loss IN WEIGHT continued.
Loss in weight during
the drying process, the
moist condition being
Plant-name.
Type of
fruit.
taken as 100, the dry
weight being then given.
Pericarp.
Seed.
Hura crepitans (Sandbox-tree) .
Woody cap-
too 34
ioo 45
sule
Ravenala madagascariensis . . .
Woody cap-
100 39
ioo 65
sule
Swietenia Mahogani (Mahogany)
Woody cap-
100 37
ioo 26
sule
Acacia Farnesiana .....
Legume
100 35
ioo 50
Csesalpinia sepiaria .....
100 24
ioo 46
Cajanus indicus .....
100 38
ioo 42
Canavalia obtusifolia ....
loo 20
ioo 41
Cassia fistula
zoo 31
ioo 40
Dioclea reflexa ......
100 31
ioo 49
Entada polystachya
100 25
ioo 45
Faba vulgaris ......
100 12 '5
ioo 40
Guilandina bonducella ....
100 14
ioo 33
Leucsena glauca .....
100 22
ioo 37
Mucuna urens
100 14
ioo 50
Phaseolus multiflorus ....
100 15
ioo 40
Poinciana regia .....
ioo 45
ioo 45
Ulex europseus ......
100 41
ioo 49
Vicia sativa 1 ,.
\ mean result
,, sepiumj
ii
ioo 32
ioo 47
PALMACE^;.
Acrocomia lasiospatha ....
Drupe
ioo 34
ioo 68
Areca Catechu ......
Berry
ioo 23
ioo 58
Cocos nucifera (Coco-nut)*
Drupe
IOO 21
ioo 53
Cocos plumosa ......
,,
ioo 63
ioo 63
Hyophorbe Verschafftii ....
Berry
ioo 15
ioo 87
Mauritia setigera . . . ...
ioo 55
ioo 57
Oreodoxa regia .....
ioo 58
ioo 81
SUMMARY OF SOME OF THE RESULTS.
Average for fleshy and pulpy berries .
Six kinds
ioo 14
ioo 57
,, typical fleshy capsules
Eight kinds
ioo 14
ioo 51
Typical fleshy drupe (Prunus) .
One kind
ioo 25
ioo 53
Average for legumes .....
Fifteen kinds
ioo 27
ioo 43
,, woody capsules
Three kinds
ioo 37
,, Palm fruits ....
Seven kinds
ioo 38
ioo 67
This result applies to a dry, waterless coco-nut.
21
322 STUDIES IN SEEDS AND FRUITS
The regime The regime of the drying fruit as indicated by the loss of
fruit. 6 rymg weight of the pericarp and the seeds can be numerically
formulated for nearly sixty plants from the data given in the
following table. If we wish to extend the inquiry by dis-
tinguishing in the case of the seed between the seed proper
and its coverings in this drying process, the data for several
of these plants will be found in Chapter IX. Should one
desire to go further and differentiate in these respects not
only between the seed-coverings and the seed proper, but also
in the case of albuminous seeds between the behaviour of the
albumen and the embryo, the requisite data for plants like
Cassia fistula, Poinciana regia^ etc., will be found in the same
chapter.
In the first place, regarding the fruit as made up of pericarp
and seeds, we can extract from the table all the elements
necessary for determining its drying regime, namely :
(<z) The weight of the moist fruit ;
() Its loss in the drying process ;
(c] The proportion of pericarp in the moist and dry fruit.
In the same way, for the seed we should require :
(a) The weight of the moist seed ;
() Its loss in the drying process ;
(<:) The proportion of the coats in the moist and dry
seed.
The subject can only be illustrated here by a few examples.
If the reader desires to work out the regime of other plants,
he will find in the table the requisite data.
THE PROPORTION OF PARTS IN FRUITS 323
ILLUSTRATIONS OF THE DRYING REGIME OF FRUITS AND
SEEDS ON THE PLANT.
(The data concerning the proportion of the pericarp to the seeds will be found in the
next table, whilst those relating to the proportions between the seed and its coverings
are given in Chapter IX. By referring to the table the elements for other plants will
be found.)
Weight in
grains.
Loss of weight
stated as a
percentage.
Relative
weight, taking
the entire fruit
or seed as 100.
Ripe
moist.
Dried.
Ripe
moist.
Dried.
Ripe
moist.
Dried.
Guilandina 1
Legume -{
Pericarp
Seeds (2)
Entire
200
zoo
400
28-4
66-3
947
IOO
IOO
IOO
14-2
33' 1
237
So
5
IOO
30
70
IOO
bonducella 1
(
Coats
61
177
IOO
29
61
5 8
Seed J
Kernel
39
15-6
IOO
40
39
42
I
I
Entire
100
33'3
IOO
33*3
IOO
IOO
(
Legume -|
Pericarp
Seeds (6)
248
152
50-4
6i'6
100
IOO
zo'3
40-5
62
1*
45
55
Canavalia 1
I
Entire
400
II2'O
IOO
28-0
IOO
IOO
obtusifolia i
f
Coats
"3
27
IOO
24
45
27
Seed -^
Kernel
137
7'3
IOO
S3
55
73
I
I
Entire
25-0
IO'O
IOO
40
IOO
IOO
Iris
Capsule -!
Pericarp
Seeds (65)
*37'5
112-5
16-3
487
IOO
IOO
11-9
43'3
55
45
25
75
Pseudacorus I
I
Entire
250*0
65^0
IOO
z6'o
IOO
IOO
(see footnote, 1
P- 324
Seed \
Coats
Kernel
072
i -08
0*14
o- S l
IOO
IOO
20
54
40
60
20
80
I
I
Entire
i '80
072
IOO
40
IOO
IOO
Primula veris I
(Primrose) j
Capsule -{
Pericarp
Seeds
Entire
1-84
2-16
4'oo
0-3
0-9
I '2
IOO
IOO
IOO
16-3
4^7
30 'o
46
54
IOO
25
75
IOO
f
Pericarp
49
6 7 -2
IOO
i V 8
70
40
Capsule -J
Seeds (i)
Entire
210
7OO
100*8
1 68-0
IOO
IOO
48-0
24*0
3
IOO
60
IOO
Seed \
Coats
Kernel
7 l' 5
'3 6 '5
28
72
IOO
IOO
38-1
S2-8
35
6<!
28
72
(
Entire
ZIO'O
IOO
IOO
47-6
IOO
IOO
324 STUDIES IN SEEDS AND FRUITS
ILLUSTRATIONS OF THE DRYING REGIME OF FRUITS, ETC. continued.
Weight in
grains.
Loss of weight
stated as a
percentage.
Relative
weight, taking
the entire fruit
or seed as 100.
Ripe
moist
Dried.
Ripe
moist.
Dried.
Ripe
moist
Dried.
(
If
Pericarp
35
5
IOO
i'4 '3
35
20
Capsule \
Seeds
65
20
IOO
30*8
*S
So
Ipomcea tuba -
(
Seed
Entire
Coats
Kernel
Entire
TOO
7'3
9-2
16-5
*5
2 '3
* 7
S'o
IOO
IOO
IOO
IOO
25-0
3^5
29-4
30-3
IOO
44
56
IOO
IOO
46
54
IOO
r r
Pericarp
5100
1869
IOO
37
85
89
Swietenia
Mahogani
(Mahogany)
Capsule -j
Seed \
Seeds
Entire
Coats
Kernel
900
6000
8-4
5'6
231
2100
074
2*96
IOO
IOO
IOO
IOO
26
35
9
53
15
IOO
60
40
II
IOO
20
80
[ I
Entire
14-0
370
IOO
26
IOO
IOO
r t
Pericarp
4250
1320
IOO
!'
8<
80
Legume -
Seeds
75
300
IOO
40*0
15
20
Entire
5000
l62O
IOO
32-4
IOO
IOO
Coats
2-63
0-6
IOO
22'8
26-3
15
Cassia fistula
Seed
Kernel
Entire
7'37
lO'OO
3 '4
4-0
IOO
IOO
46'!
4O'O
737
lOO'O
85
IOO
Coats
a-6,
o'6o
IOO
22-8
26-,
15
Seed
Albumen
5'37
2*64
IOO
49'2
537
66
Embryo
2'OO
076
IOO
38*0
20 '0
!9
I *
Entire
10*00
4 'oo
IOO
40 'o
100*0
IOO
Arum
maculatum
(
Berry -1
Pericarp
Seeds (3)
Entire
4'2
2'8
7-0
o'6i
1-42
2-03
IOO
IOO
IOO
H-S
507
29 'o
60
40
IOO
3
70
IOO
Pyras Malus
(Apple)
| Berry
Pericarp
Seeds (10]
Entire
993
7
1000
136-4
3-6
140*0
IOO
IOO
IOO
!37
5* '4
14*0
99'3
7
lOO'O
97 '4
2-6
lOO'O
Note that in some cases, as in Iris Pseudacorus, there is a slight difference between
the loss of weight of the entire seed, as given under the fruit and under the seed. This
is due to the aborted seeds being included in the first case.
THE PROPORTION OF PARTS IN FRUITS
325
TABLE CONTAINING THE ELEMENTS FOR THE DETERMINATION OF THE
DRYING REGIME OF FRUITS AND SEEDS AS ILLUSTRATED IN THE PAGES
PRECEDING.
(The only natural orders indicated are the Palmacese by P. and the Leguminosse by
L. before the plant's name. Further details will be found in Note 28 of the Appendix
for those plants where N. follows the name.)
Weight-
Loss of
Type
of
Average
weight
of a
moist
Number
of
seeds
relation of
the pericarp,
taking the
entire fruit
weight of
fruit when
air-dried,
taking the
fruit.
fruit
in fruit
as ioo.
moist fruit
in
grains.
tested.
as ioo, the
dry weight
Moist
Dry
being then
fruit.
Fruit.
given.
Pyrus Malus (Apple), N.
Berry
900
10
99 '3
97 '4
ioo 14
Citrus Aurantium (Common
,,
2400
5
99 '3
98-3
ioo 19
Orange), N.
Citrus Aurantium( Mandarin
,,
1900
5
99-0
Orange)
Citrus decumana (Shad-
,,
14,000
80-85
97
dock), N.
P. Cocos nucifera (Coco-
Drupe
60,000
i
96
78
ioo 30
nut), N.
Ribes Grossularia (Goose-
Berry
120
40
95
80
ioo 15
berry), N.
Prunus communis (Sloe), N.
Drupe
3
i
95
90
ioo 27
Achras Sapota (Sapo-
Berry
1000
5
95
dilla), N.
Sambucus nigra (Elder), N.
,,
3'5
3 or 4
93
60
IOO 21
P. Acrocomia lasiospatha, N.
Drupe
55
i
92
85
ioo 36
P. Acrocomia sclerocarpa
,,
i
89
...
P. Cocos plumosa, N. .
,,
IOO
i
91-6
91*6
ioo 63
P. Arenga saccharifera, N.
it
600
i
9
80
ioo 50
Psidium Guajava (Guava) .
Berry
600
300
90
Momordica Charantia, N. .
Capsule
500
15
89
51
ioo 15
Opuntia Tuna (Prickly
Berry
800
90
89
7
ioo 18
Pear), N.
. Tamus communis
,,
H
4015
87
5
ioo 18
Ravenala madagasca-
Capsule
700
10 or 12
87
80
ioo 42
riensis, N.
Lonicera Periclymenum, N.
Berry
5
5
86
66
ioo 25
(Honeysuckle)
L. Cassia fistula
Legume
5000
95
85
80
ioo 32'4
Sparganium ramosum, N. .
Swietenia Mahogani
Drupe
Capsule
i
5800
i
60
85
85
84
89
ioo 45
ioo 35
(Mahogany), N.
Hura crepitans (Sandbox-
ii
3000
4
84
80
ioo 36
tree), N.
Barringtonia speciosa, N. .
L. Poinciana regia, N. .
Berry
Legume
9000
3500
i
40
la
80
52
80
ioo 15
ioo 45
L. Entada polystachya, N.
,,
800
Z 4
75
62-5
ioo 30
L. Csesalpinia Sappan .
,,
260
4
75
75
ioo 50
Theobroma Cacao, N.
Berry
7000
45
75
326 STUDIES IN SEEDS AND FRUITS
TABLE CONTAINING THE ELEMENTS, ETC. continued.
Average
Weight-
relation of
Loss of
weight of
fruit when
Type
of
weight
of a
moist
Number
of
seeds
the pericarp,
taking the
entire fruit
air-dried,
taking the
moist fruit
fruit.
fruit
in fruit
as loo.
as 100, the
in
tested.
dry weight
grains.
Moist
Dry
being then
fruit.
fruit.
given.
P. Areca Catechu (Areca-
Berry
250
i
74
53
too . 32
nut), N.
Thespesia populnea .
Baccate
230
13 or 14
7*
45
100 33
capsule
L. Ulex europseus .
Legume
3
4015
70
66
loo 43
Scilla nutans
Capsule
10
20
70
20
100 25
^Esculus Hippocastanum,
>
700
I
70
4
IOO 24
N. (Horse-chestnut)
Monstera pertusa, N.
Berry
5
I
66
30
IOO 2O
P. Hyophorbe Verschafftii
,
'5'5
I
05
24
ioo 40
P. Oreodoxa regia, N. .
,
15
I
64
56
loo 66
L. Caesalpinia sepiaria . .
Legume
IOO
5
64
4 8
ioo 32
L. Canavalia obtusifolia .
400
6
62
45
ioo 28
L. Canavalia gladiata, N.
6
45
L. Canavalia ensiformis, N. .
H
44
L. Mucuna urens .
IOOO
3 or 4
61
3'
ioo 28
L. Andira inermis .
*35
i
61
53
ioo 40
L. Pisum sativum (Pea) .
250
7 or 8
60
20
IOO 20
L. Phaseolus multiflorus
300
4
60
36
ioo 25
(Scarlet- runner)
L. Phaseolus (tropical species)
3
34
Arum maculatum
Berry
7
3
60
3
ioo 29
Hedera Helix (Ivy) .
5
3
59
5 2
ioo 40
Datura Stramonium .
Capsule
300
600
5
24
ioo 30
Bignonia, near sequinoc-
Siliqui-
1240
55
56
3
ioo 40
tialis, N.
form
capsule
Allium ursinum .
Capsule
2-4
3
56
29
ioo 33
Iris Pseudacorus
)>
250
80
55
2 5
ioo 26
L. Vicia saliva
Legume
i5
10
5
40
ioo 37
L. Vicia sepium
11
6
3 or 4
5
40
ioo 42
L. Faba vulgaris (Broad
800
5
5
24
ioo 26
Bean), N.
Artocarpus incisa (Bread-
Aggregate
12,000
60
5
fruit)
L. Guilandina bonducella
Legume
400
2
5
30
ioo 24
L. Dioclea reflexa . . .
i>
1800
4
47
36
ioo 41
L. Cajanus indicus
40
4
47
45
ioo 40
L. Leucaena glauca, N. .
11
IOO
24
47
35
ioo 30
Primula veris (Primrose), N.
Capsule
4
62
46
2 5
ioo 30
P. Mauritia setigera, N.
Berry
IOOO
i
46
45
ioo 56
Aquilegia, N. .
Follicular
10
IOO
46
24
ioo 45
capsule
L. Acacia Farnesiana
Legume
150
20
46
40
ioo 40
Iris foetidissima .
Capsule
1 80
40
43
34
ioo 25
Canna indica, N. . '.
IOO
24
39
ii
ioo 47
Ipomo2a tuba .
IOO
4
35
20
ioo 25
Arenaria peploides
8
10-12
2 5
9
ioo 41
Quercus Robur (Oak), N.
Nut"
60
35
19
ioo 40
THE PROPORTION OF PARTS IN FRUITS 327
TABLE SUPPLEMENTARY TO THE PRECEDING AND RELATING ONLY TO THE
PERICARP-RELATION OF THE AIR-DRIED FRUIT, THAT FOR THE MOIST
LIVING FRUIT BEING NOT ASCERTAINED, EXCEPT IN THE CASE OF
COCOS, WHERE TWO SPECIES FROM THE PREVIOUS TABLE HAVE BEEN
ADDED FOR THE PURPOSE OF COMPARISON.
(See the preceding table for explanation. N. = Note 28 of the Appendix.)
Type of fruit.
Average weight
of a dry fruit
in grains.
Weight-relation
of the pericarp,
taking the
entire dry
fruit as 100.
L. Abrus precatorius (4 or 5 seeds) .
Legume
8
*5
L. Albizzia Lebbek (7 or 8 seeds), N.
ii
?8
55
Anacardium occidentale (Cashew)
Nut
95
66
P. Bactris (species of), N.
Drupe
170
67
L. Bauhinia (18 seeds)
Legume
300
78
Cakile aequalis, N.
Lomentaceous
o'7
7 1
siliqua
,, maritima, N. .
do.
0-9
70
P. Caryota (species of) with 2
Drupe ?
80
26
seeds, N.
P. Cocos schizophylla ? N.
500
65
,, nucifera (Coco-nut), N.
16,000
78
,, plumosa, N.
,,
63
91*6
L. Cynometra (species of) with i
Legume
200
26
seed
P. Elseis guineensis, N. .
Drupe
120
85
L. Erythrina corallodendron (7 or 8
Legume
40
4i
seeds), N.
L. Erythrina indica (10 seeds) . . ,,
I4O
35
Gossypium barbadense (16
Capsule
31
28
seeds) N.
Gossypium hirsutum (23 seeds) N.
>j
50
24
Hibiscus esculentus ( i o carpels) N.
51
IOO
30
Kleinhovia hospita (5 seeds)
1)
r6
5
P. Licuala grandis ....
Berry
10
42
P. Livistonia (species of)
,,
*5
49
Moringa pterygosperma (15 seeds)
Siliquiform
170
62
capsule
P. Prestoea montana
Berry
18
3
Ricinus communis (Castor-oil), N.
Coccous
12
5
capsule
Rumex .....
Nut
o'o8
30
P. Sabal umbraculifera .
Berry
10
44
Saccoglottis amazonica (2 seeds)
Drupe
33
94
Scirpus maritimus
Nut
o'oy
5
Terminalia Catappa, N.
Drupe
no
95
Viola tricolor (40 seeds)
Capsule
*'&
5
328 STUDIES IN SEEDS AND FRUITS
SUMMARY
(1) This chapter deals with the weight-relations between the peri-
carp (fruit-case) and the seeds in the different stages of a fruit's history,
and it involves a special inquiry into the drying of the mature fruit.
(2) After pointing out that for purposes of comparison the fruit
in the moist living condition is far more important than in the dried
dead state, the author illustrates his method of investigation by taking
the fruit of Barringtonia speciosa (p. 294).
(3) The relative weights of pericarp and seeds in sixty-four
mature fruits before drying begins are then discussed, and the results of
the author's observations are tabulated (p. 297)
(4) With regard to the influence of the type of fruit on this
relation, it appears that fruits possessing the greatest proportion of
pericarp, that is to say, where the weight of the fruit-case is more
than 90 per cent, of that of the whole fruit, are either berries or
drupes (p. 299).
(5) In determining the weight-relation, " size " counts for little
with drupes and berries. Thus about 2OOO drupes of Prunus communis
(Sloe) make up the weight of a single green fruit of the Coco-nut Palm,
and nearly 5000 Elder berries (Sambucus nigrd) are required to weigh
down an average fruit of the Shaddock (Citrus decumana). Yet the
proportions of pericarp and seeds are much the same in the two cases.
With legumes the largest and heaviest fruits have the smallest seed-
weight, a rule usually but not always applicable to capsules also (p. 300).
(6) The history of the weight-relations between the fruit-case
and the seeds in different stages of the fruit's development is then
dealt with, and it opens up a study of the growing, ripening, and
drying fruit (p. .301).
(7) It is observed that whilst in the younger fruits the growth of
the fruit-case is far in advance of that of the seeds, both fruit-case and
seeds usually reach maturity about the same time.
(8) Yet there are fruits where seeds continue their growth after
the fruit-case has begun to dry. This is exemplified in the fruits of
the Coco-nut Palm (Cocos nucifera\ of the Oak (Quercus Robur\ and
probably also of Barringtonia speciosa. The cases of the two first-
named are discussed with much detail, the results largely of the
indications of the balance. That of the coco-nut, which was studied
by the author in the West Indies, is first dealt with, and it is shown
that the seed grows markedly whilst the husk is drying. That of the
acorns of the Oak, which was investigated by the author in Devonshire,
is treated at length, and it is established that the seed of the acorn
continues its growth after the shell has begun to dry (pp. 301-314).
THE PROPORTION OF PARTS IN FRUITS 329
(9) This occasional tendency of a seed to continue its growth
after the fruit-case or pericarp has begun to dry, or, in other words, to
die, finds its final expression in the germination of the seed on the
plant. To put it in another way, it is a step towards vivipary.
(10) Reference is then made to the principle established by the
results tabulated in this chapter, that as the fruit grows, matures, and
dries, the proportion by weight of the pericarp decreases and that of
the seeds increases. This is merely stating in other words the familiar
fact of observation that the earlier history of a fruit's development is
mainly concerned with the fruit-case and the later history with the
seed. As illustrating this principle for the legumes, the pods
of the Scarlet-runner (Phaseolus multiflorus) and of the Broad Bean
(Faba vulgans] are specially discussed, the fruits of Iris Pseudacorus being
taken for the capsules, whilst the acorn is also referred to. Small
departures from this rule are noticed in the cases of the coco-nut and
of the fruits of Iris fcetidhsima and Barringtonia speciosa (p. 315).
(u) Attention is then called to the significance of the fact that in
the drying fruit the pericarp loses far more water than the seed, the
result being that whilst the fruit-case dies the seed lives. Whilst on
the average the pericarp of the moist fruit loses between 75 and 80
per cent, of its weight, the seed as a rule loses only half its weight
(P- 3i8).
(12) When we compare the different fruit-types we find that it is
in the behaviour of the pericarp in the drying process that most varia-
tion is displayed, the seeds being much more constant in this respect.
Thus on the average fleshy capsules and pulpy berries lose 86 per cent,
of the weight of the moist pericarp when drying on the plant, fleshy
drupes 75 per cent., legumes 73 per cent., woody capsules 63 per cent.,
and palm fruits 62 per cent (p. 318).
(13) A method of numerically formulating the drying regime of
fruits is then described and illustrated, and in a special table are
given the elements of this determination for nearly sixty plants (p. 322).
CHAPTER XV
The relation
between the
number of
seeds and the
weight of a
fruit,
(a) in the
living fruit.
THE RELATION BETWEEN THE NUMBER OF SEEDS AND THE
WEIGHT AND SIZE OF THE FRUIT
THE relations between the number and weight of the seeds
on the one hand and the total weight of the fruit and the
proportional weight of the pericarp on the other offer an
interesting study. Although we shall at first treat the subject
on its own ground, it will soon be perceived that in so doing
we are ignoring important determining influences. Foremost
among such influences stands that connected with the abortion
of ovules before and after fertilisation, this distinction in time
with regard to fertilisation being pregnant with results as regards
the future of the fruit. But the subject of the failure of ovules
and seeds is dealt with in Chapter XVI., and here it will be
only incidentally noticed as we proceed with the discussion.
The living fruit, that is to say, the green, moist, full-grown
fruit with large, soft, uncontracted seeds, first claims our
attention. This is but natural, and indeed the main interest
of the withered or air-dried fruit should chiefly lie in its ability
to aid us in our studies of the living fruit. Although the
data below tabulated are scanty, their acquisition has often
involved a good deal of labour, and a large amount of material
had usually to be gone over to get a few results. It is necessary,
for instance, to select only full-grown moist fruits that show no
signs of drying ; but of these a large number have frequently
to be rejected on account of defective seed-development, or
of a lack of uniformity in the size of the seeds.
33
SEED-NUMBER AND FRUIT-SIZE
TABLE SHOWING THE RELATION BETWEEN THE NUMBER OF SEEDS IN
CAPSULES AND LEGUMES, AND THE PROPORTIONAL WEIGHT OF
THE PERICARP IN FULL-GROWN FRUITS BEFORE DRYING BEGINS.
Proportions o:
Ranges.
pericarp and
Number
of
seeds.
Number
of
fruits
ex-
amined.
Average
total
weight
of a
fruit in
grains.*
seeds, taking
the weight of
entire fruit
as 100.
Aver-
age
weight
of a
seed in
grains.
Pericarp
pro-
portions.
Total
weight of
fruits in
Peri-
grains.
Seeds.
carp.
^Esculus Hip-
pocastanum
(capsule).
f:
8
6
650
920
72
67
28
33
182
150
64-78
61-75
450- 900
600-1140
( 13
i
6 5
46
54
2 7
Canna indica
1 '9
i
85
59
2-6
(capsule).
i
IOO
39
61
27
I 25
i
108
37
63
27
...
Iris
Pseudacorus
(capsule).
f 37-5
| 67-77
(.84-86
2
4
2
161
265
353
62-5
54 -o
SS'S
37'5
46*0
44 '5
i '4
i|9
60*2, 647
50-60
5i'4, 59'5
137, 186
246-288
35> 357
Iris
132
46*0
54-0
2'6
foetidissima
\ "
172
44 '6
55 '4
27
. .
(capsule).
(11
196
207
44 'i
41-1
55'9
58-9
2'8
2'8
Csesalpinia
216
74'5
25 '5
18-3
Sappan
I 4
240
75-6
24-4
14-8
.
(legume).
(^ 5
272
74 '9
25-1
13-6
Dioclea f
reflexa
] 3
1341
46-8
53 '2
238
(legume).
I 4
1814
47'3
527
239
Guilandina
bonducella
f x
2
260
68-0
32-0
81-0
(legume).
I 2
2
33
56*0
44 -o
73'
...
r 5
I
199
61
39
15*4
Pisum t
6
I
167
64
36
10 '0
sativum
6
I
138
58
42
97
IM
(legume).
7
I
198
62
38
t 9
I
290
57
43
13-9
...
* In the case of single fruits the actual weight is given.
t The average length of the 3 -seeded pods is 127 millimetres, and of the 4-seeded
pods 152 millimetres.
I Two sets of pods are here represented, the first and last belonging to one season,
and the others to another season.
For capsules with a few large seeds, the behaviour of that of Capsules and
the Horse-chestnut (Msculus Hippocastanum) would probably be
typical. Out of the original six ovules, not more than two
or three develop into mature seeds ; and fruits with a single
332 STUDIES IN SEEDS AND FRUITS
seed are not infrequent. The capsules with one and two seeds
are best suited for comparison in this respect. In passing
from the single to the double-seeded fruit of full size and
showing no signs of dehiscence or drying, fruits with the seed
or seeds in soft white coverings and the embryo normally
developed, we find
(1) An increase of about 40 per cent, in the total weight of
the fruit ;
(2) A decrease in the proportional weight of the pericarp
from 72 to 67 per cent ;
(3) A decrease of about 1 8 per cent, in the weight of each
seed.
With many-seeded capsules, as with those of Canna and
Iris, we also find that a marked increase in the total weight of
the fruit and a gradual decrease in the relative weight of the
pericarp accompany the additions to the number of seeds,
' but the average weight of a seed seems usually to remain
unchanged. All these are merely indications, and appeal for
confirmation will be made subsequently to results estimated
from the dry fruits.
The data for the living legume are too scanty, and
will have to be supplemented by results obtained from dried
fruits.
(6) In the We now come to the question of the use of the dried or
dried fruit w ithered fruit in determining the relation between the number
of seeds and the proportional weight of the pericarp. Naturally
such an investigation is far easier with dried or withered fruits
than with moist mature fruits that have not begun to lose
weight in drying. We can furnish ourselves from the plant
with abundant materials in all stages of drying, and where
further drying is needed it can be readily accomplished at
home. But the case becomes very different when we make
use of moist fruits. Here it is necessary to select only those
fruits which a previous study has shown to have reached their
maximum growth, but have not yet begun to dry ; and this
is not always so easy as it seems. Then, again, the question as
SEED-NUMBER AND FRUIT-SIZE 333
to which of the two sorts of fruits offers the best materials,
the moist or the dry, has to be answered with another query
as to whether the two results would be really comparable and
would possess a biological importance similar in degree and in
kind.
As far as the dry fruit is concerned, it is requisite to
remember that we are here actually determining the relation
between a resting seed with its vitality suspended and a dried-
up and dead fruit-case. Whether it is a shrivelled berry or
a shrunken drupe, as in Ribes and Prunus, or a dried dehiscing
pod, as in Vida^ or a withered capsule, as in Iris and Canna, or
a woody dry capsule, like that of the Mahogany (Swietenia),
that on account of the abundance of ligneous tissue retains
the form of the moist fruit, makes no difference. The mere
retention of form in some dried fruits, as in certain kinds of
legumes and capsules, and its complete loss in others, as in
most drupes and berries, are merely accidents in the history of
the fruit. The investigator does not recognise the distinction
between moist and dry fruits in the living condition. For
him all fruits are moist in the living state ; and if, after the
drying up and death of the fruit-case, the form of the living
fruit is to some degree preserved, he will avail himself of the
circumstance only in so far as it assists him in his studies of
the living condition.
It would therefore appear that the moist and the dry fruit i he data
are not mutually comparable, and that the only comparison of drwsd-up 7
any biological value is one which enables us to reconstitute the frults * re
living fruit, when the only materials at our disposal are its service when
dried-up remains. The loss in weight which the pericarp and the living
seeds of the living fruit undergo when dried in ordinary air- condltion -
conditions can be ascertained by experiment, and the results
can be applied to the dry fruit. These shrinkage ratios, being
constant for the same species and independent of the size of
the fruit, do not, when applied, interfere with the progressive
scale of the weight-relations between the pericarp and the
seeds. In this sense, therefore, the data supplied by the dry
334
STUDIES IN SEEDS AND FRUITS
The dry
legumes of
Leucsena
glauca and
Albizzia
Lebbek.
fruit can be utilised ; and as long as the means of converting
them are available, the actual conversion may be at times
dispensed with.
The validity of this use of the dry fruits is brought out in
the two following tables, which contain the results of observa-
tions in Grenada on a considerable number of the dry legumes
of Leuc<ena glauca and Albizzia Lebbek. In the first table the
results for the dry legumes are alone given. In the second
table these results are compared with those for the moist fruits
as far as the relative weights of the pericarp and seeds are
concerned. It should, however, be added that whilst the
shrinking ratios for the legumes of Leuc<ena glauca have been
ascertained by experiment, those for Albizzia Lebbek have been
A. TABLE COMPARING THE RELATION BETWEEN THE NUMBER OF
SEEDS AND THE WEIGHT, LENGTH, AND PERICARP PROPORTIONS
OF THE DRIED LEGUMES OR PODS OF LEUOENA GLAUCA AND
ALBIZZIA LEBBEK.
Proportional weight
Average weight
.
of pericarp and
Number
of seeds
in a
pod.
Number
of pods
ex-
amined.
Average
length
of a pod
in milli-
metres.
in grains.
A.vcr~
age
weight
of a
seed in
grains.
seeds, taking the
entire pod as 100.
Entire
pod.
Peri-
carp.
Seed
con-
tents.
Peri-
carp.
Seeds.
Entire
pod.
(
IO-I2
6
114 mm.
127
4 '9
7'8
072
38-6
61*4
100
Leucsena J
13-17
ii
130
14-8
S'*
9-6
o'68 35-1
64-9
IOO
glauca )
20-ZI
7
'73
24-6
8'7
'5'9
077
35'4
64-6
IOO
(
22-26
9
i9S
29*0
IO'I
18-9
078
34*8
65-2
IOO
.
I
10
142
8-80
6-52
2*28
2*28
74'i
25-9
IOO
2
14
i So
1370
9-11
4'59
2*29
66*5
33'5
IOO
3
*3
193
1778
11*22
6-56
2*19
63-1
36-9
IOO
4
3
218
2275
1 3 '99
876
2-19
61-5
3^5
IOO
5
12
228
27 '45
16-80
10-65
2-13
61-2
38-8
IOO
Albizzia
6
IO
236
3 l 'S*
18-99
12-53
2-09 6o'2
39-8
IOO
Lebbek '
7
8
251
35-20
19-58
15-62
2*23 55-6
44 '4
IOO
8
8
262
39 '77
22'3O
17 '47
2*18
56*1
43 '9
IOO
9
9
254
40-07
22*05
I 8 -02
2*00
55'
45-0
IOO
10
ii
290
49 "39
26*92
22-47
2-24
54'5
45 '5
IOO
ii
8
282
51-26
28-50
22-76
2*07
55-6
44 '4
IOO
12
10
294
59-42
34'43
24-99
2 '08
S7'9
42-1
IOO
SEED-NUMBER AND FRUIT-SIZE
335
B. TABLE COMPARING THE RELATION BETWEEN THE NUMBER OF
SEEDS AND THE WEIGHT OF THE ENTIRE FRUIT AND ITS PARTS
IN THE MOIST AND DRY CONDITION FOR THE LEGUMES OF
LEUOENA GLAUCA AND ALBIZZIA LEBBEK.
(The shrinking ratios for the last-named have been estimated as explained in the
remarks below.)
Average weight
Relative weights, taking the
entire pod as 100.
Number
in grains of
of seeds
entire pod.
in a
Pericarp.
Seeds.
pod.
Moist.
Dry.
Moist.
Dry.
Moist.
Dry.
10-12
41-8
127
53'4
38-6
46-6
6 1*4
Leucsena glauca
13-17
20-21
47 '6
79'3
14-8
24 '6
49-6
49 -8
35'i
35 '4
50-4
50-2
64-9
64-6
22-26
93-2
29 - o
49-2
34-8
50-8
65-2
I
3' 78
8-80
82-1
74'i
17-9
25-9
2
47'9i
13-70
76-1
66-5
23-9
33'5
3
61-28
17-78
73-2
63-1
26-8
36-9
4
77-86
2275
71-9
6.- 5
28-1
38-S
5
93-82
2 7'4S
71-6
61-2
28-4
38-8
Albizzia Lebbek
6
7
107 '28
"7'37
3 I- S 2
35-20
70-8
66-8
60*2
55'6
29-2
33-2
39'8
44 '4
8
135-87
39'77
65-7
56-1
34*3
43'9
9
i irz$
40-07
66-2
55 "o
33'8
45-0
10
163-85
49'39
657
54'5
34 '3
45'5
ii
1 70 '90
51-26
66-7
55-6
33'3
44 '4
12
200-19
59-42
68-8
S7'9
.3 1 **
42-1
The shrinking ratios employed for Leucana glauca are 100 - 22 for the pericarp, and
100-40 for the seeds; the pericarp thus losing 78 per cent, of its weight in the drying
process, and the seeds 60 per cent.
The ratios used for Albizzia Lebbek are 100-25 for the pericarp, and 100-60 for
the seeds.
estimated, as I had no opportunity of experimenting on the
living fruits. On the average, in moist mature legumes of
this character the pericarp loses about 75 per cent, of its weight
during the drying process, whilst the weight of the seeds is
diminished by about 60 per cent. ; and these are the ratios
applied to the dry Albizzia pods. The estimate for the moist
fruit thus obtained cannot be far wrong, and since any error
would uniformly affect all the results, the relations between
them would be unaffected.
336 STUDIES IN SEEDS AND FRUITS
Inferences to We find the answer to the question suggested by the
fron^the 11 columns of Table A as to the relative values of the data
tabulated afforded by moist and dry legumes in the contents of Table B.
results above i i i i i i ,
given. Here we see that although the relative proportions by weight
of pericarp and seeds are on different planes, the pericarp being
proportionately lighter and the seeds proportionately heavier
in the dry than in the moist fruit, the progressive changes
of relation are the same in both. We thus arrive at the
following conclusions with regard to the relations between
the number and weight of the seeds, the weight and length
of the pod, and the relative proportions of the pericarp, in the
living legumes of Leuc^na glauca and Albizzia Lebbek.
(a) It is only in the few seeded pods of each plant that the
legumes follow the principle of capsules, where not only a
marked increase in the weight and size of the entire fruit,
but a gradual decrease in the relative weight of the pericarp
accompanies the additions to the number of seeds.
() But this principle has a limit in each case. In Leuc<ena
glauca it is restricted to the shorter pods with less than a dozen
seeds. In Albizzia Lebbek it is confined to the shorter pods
with less than seven seeds. Beyond these limits in- both cases,
as the seeds increase in number and the pods increase in
length, the relative proportions of the pericarp and the seeds
remain about the same.
(c) The average weight of a single seed varies but little,
whatever may be the number of seeds or the length of the
legume. A slight increase of weight is indicated in the case
of the longer pods of Leuc<ena glauca ; but I do not imagine
that this small difference would have been sustained if the
materials had been more abundant.
Theindica- The weight-relations of the pericarp in some other dried
dried Cr legumes, as shown by those of Vicia^ Ulex, and Erythrina in
legumes. t h e following table, give no very definite results, the tendency
of the decrease in the relative weight of the pericarp, as the
fruits increase in size and weight and the seeds in number,
being but slight. However, in Guilandina bonducella, which has
SEED-NUMBER AND FRUIT-SIZE 337
usually one or two large seeds in each pod, there is a decided
repetition of the behaviour of capsules in these respects, thus
supporting the conclusion derived from the legumes of Leucxna
glauca and Albizzia Lebbek that it is the pod with few seeds
that is most likely to follow the principle of the capsule.
But even in such a case this seems only to apply to legumes
with a few large seeds. More often it would be difficult in
small pods containing only a few seeds to discover any such
relation. Thus there is certainly but little to be made out of
the results for Abrus precatorius given in the following table,
in the columns of which data for larger legumes, like those
of Canavalia obtusifolia> will be found, which are equally
indeterminate in their indications. Doubtless the scantiness
of the materials is partly responsible for this ; but we might
have looked for some more consistent results than are given
for dry legumes in the subjoined table. There are evidently
some disturbing influences at work that cause this irregularity
in the relations between fruit and seed in these legumes.
These influences, as will subsequently be shown, are connected
with the failure of seeds and the abortion of ovules.
One disturbing cause is needlessly brought into action
when we employ indiscriminately legumes that have dried on
the plant and those that have dried in an experiment. A
serious effect may be thus produced, a matter discussed in
Note 1 6 of the Appendix. This influence has, however, been
avoided in my own results by using for each plant only fruits
dried in the same way.
Coming to the evidence of dried capsules, like those of
Iris Pseudacorus and Iris fcetidisslma^ we find the features of the
moist capsule reproduced in the following table. As the
fruit increases in size and weight and in the number of its
seeds, the proportion of the pericarp steadily decreases, but,
unlike the moist fruits, there is an increase in the weight of
the individual seed. Other types of capsules, such as those
illustrated by the siliquiform fruits of Moringa pterygosperma,
seem to follow the same rule.
22
338
STUDIES IN SEEDS AND FRUITS
TABLE SHOWING THE RELATION BETWEEN THE NUMBER OF SEEDS AND
THE PROPORTIONAL WEIGHT OF THE PERICARP IN DRY LEGUMES
AND CAPSULES.
(In the case of all the legumes and of the Moringa capsules the fruits had dried on the
plant ; whilst the Iris capsules were allowed to dry slowly in my room.)
Plant
Number
of seeds
Number
of fruits
Average
length of
a fruit
Average weight
in grains.
Aver-
age
weight
Proportional weight
of pericarp
and seeds.
in a
fruit.
ex-
amined.
in milli-
metres.
Entire
fruit.
Peri-
carp.
Seed
con-
tents.
of a
seed in
grains.
Peri-
carp.
Seeds.
Entire
fruit.
Vicia
sepium
(legume).
(4 or 5
8
4
30
35
2-36
3 '99
0-93
"'43
2 '44
o'33
0-27
39*4
38-9
60-6
61-1
IOO
IOO
Ulex
( 4
3
147
1-23
0-83
0*40
0*10
67-6
32*4
IOO
europaeus
-I 5
5
...
1-24
0-82
0*42
o'o8
66-1
33'9
IOO
(legume).
I 6
3
H7
i '47
'93
0-54
0*09
63-6
36-4
IOO
Erythrina
corallo-
(3 or 4
f
2
57
7'6
2 '2
42-9
S7'i
IOO
dendron
5 or 6
4
27-3
117
15-6
2'8
42-9
57' 1
IOO
(legume).
7-9
5
41-6
17*0
24*6
3' 1
40-9
59' 1
IOO
Guilandina
bonducella
(legume).*
1 *
6
5
...
53*3
88-0
20-8
27-2
60-8
30-4
39 -o
30-9
6i'o
69'!
IOO
IOO
/ 37
36-2
14-2
22*0
o - 6o
39-2
6o'8
IOO
Iris Pseu-
1
...
43'3
14*6
287
0-57
337
66-3
IOO
dacorus
J 63
...
62*3
16-3
46^0
070
26-2
73'8
IOO
(capsule)
74
85
70*0
80 'o
17-0
20 '0
53'
60 'o
072
071
24-3
25-0
757
75 '
IOO
IOO
V 96
93'3
23'0
7'3
073
247
75'3
IOO
Iris foeti-
dissima
(capsule).
1 19-35
[40-55
5
5
...
32-4
587
12-6
17-9
19-8
40-8
072
o 90
38-9
30-5
6n
69-5
IOO
IOO
Moringa
f
pterygo-
sperma
(siliquiform
} lz
1 I6
228
266
'178
84
no
47
68
4-0
4 '3
64-1
61-8
35 '9
38-2
IOO
IOO
capsule).
V
( 3
5-6
2'0
3-6
'2
357
64-3
IOO
Abrus pre-
catorius
J
...
8-0
7 '2
2'2
I-6 5
5'55
'4
'4
22-9
72-5
77-1
IOO
IOO
(legume).
'
...
7'3
9-0
1-8
27
S'S
'4
'3
247
30*0
75'3
7o'o
IOO
IOO
I 5
9-0
2'I
6-9
'4
23-3
767
IOO
Canavalia
f !
'33
54
79
I3'2
40 '6
59 '4
IOO
obtusifolia
i 6
123
57
66
II'O
46-3
537
IOO
(legume).
1 8
I 8
156
146
60
63
96
83
12*0
io'4
43-i
61-5
56-9
IOO
IOO
* These pods were all gathered in the dried dehiscing condition at the same time from
the same plant.
SEED-NUMBER AND FRUIT-SIZE 339
Summing up the indications of the influence of the number Summary
of seeds on the proportion of parts in capsules and legumes,
we find that the capsule, as illustrated by the fruits of 7m,
Canna^ and SEsculus^ in response to the augmentation of the of seeds on
i r j 1-11-1 T.1 the fruit in
number ot seeds acquires a relatively lighter pericarp. The the case of
fruit increases in size and weight ; but this increase is due
more to the seeds than to the fruit-case. The legume, as
typified by the fruits of Leucxna glauca and Albizzia Lebbek,
follows the principle of the capsule in the few-seeded pods ;
but in the many-seeded fruits it preserves a fairly constant
relation between the weight of the pericarp and the seeds,
the pod increasing regularly in length and weight as the seeds
increase in number. But the other results obtained for
legumes often give no definite clue to any such relations,
except in the case of pods with a few large seeds, as in
Guilandina bonducella^ where the principle of the capsule is
indicated by both the moist and the dry fruits. This lack of
relation is partly due to insufficiency of materials ; but in the
case of small pods with a few seeds, like those of Abrus and
[//<?#, there is evidently some disturbing cause which largely
counteracts the display of a connection between the number
of seeds and the size of the pod. The circumstance of the
growth of the legume being linear, rather than tangential, as in
the capsule, may help to explain why the first-named is more
irregular in its behaviour. For this reason also the legumes
would be more liable to be affected by the abortion of ovules
and the failure of seeds.
As regards the alterations in the average weight of a seed The degree
with the accession to the number of seeds and with the increase f the weight
in the weight and size of the fruit, the results seem to justify
the following conclusions : different size
(a) In the case of many-seeded capsules, like those of Iris
and Canna, we find that as the fruit increases in size and the
seeds in number, the seeds of Iris increase their weight, whilst
those of Canna remain unchanged. But when a capsule
matures only one or two large seeds, as with the Horse-
340 STUDIES IN SEEDS AND FRUITS
chestnut (Msculus Hippocastanum\ the seeds of the two-seeded
fruits are smaller and lighter than those of the single-seeded
fruits, in this case the decrease in weight being about 18
per cent.
() With regard to legumes the indications supplied by
the 126 dry pods of Albizzia Lebbek are particularly valuable,
all of them being obtained at the same time from the same
tree. Here the seeds range in number from i to 12 ; and
for each number of seeds from 8 to 13 pods were employed.
Here it will be seen that whilst the legume doubles its length,
and increases its weight sevenfold, the average weight of a
seed changes but little. The extreme range of the variations
amounts to only about 13 per cent, of the average weight
of the seed, the variations themselves being evidently
fortuitous in character. The testimony of the legumes of
other plants named in the tables cannot carry much weight,
because the materials are insufficient. But I would gather
from the cases of Ulex europ<eus and Abrus precatorius that with
small pods the seeds keep their weight as they increase in
number and the pods increase in size.
The study of And now, before leaving this subject of the relation
between the between the number of seeds and the weight and size of
t ' ie ^ ru ^ anc ^ its parts, it is necessary to point out that,
proportions however suggestive the indications may be, we have not yet
opens up a discovered an end of the thread of this tangled problem.
problem. Yet these figures may serve to direct our efforts in the right
direction. Thus the first question they will lead us to put
will be the very pertinent one relating to the causes and
nature of the variation in the number of seeds in the fruits
of the same individual plant. If the relative size of the
fruit is determined on fixed principles by the number of
seeds, it would be natural to inquire what determines the
number of seeds.
But several subsidiary questions arise when we peruse
the columns of the tables. Why, for instance, does a single-
seeded pod differ from other many-seeded pods on the same
SEED-NUMBER AND FRUIT-SIZE 341
plant in the exceptional proportion of its pericarp ? In the
single-seeded fruits of Albizzia Lebbek the large size of the
pod in relation to the solitary seed is very conspicuous. But
those interested in the subject will call to mind other legu-
minous plants displaying fruits of the same character. Let
us take, for example, the pods of Cytisus Laburnum and of
Sophora tetraplera. Occasionally they contain only a single
seed ; and in such cases it will not be necessary either to
measure or to weigh them in order to perceive that, as
compared with the typical many -seeded fruits, the size of
the pod is quite disproportionate. However, if we rip open
one of these single-seeded legumes, and examine the interior
carefully, we make a discovery. There is, it is true, only
one seed, but we can discern with a lens the remains of
all or most of the missing ovules that existed in the ovary
before pollen was applied to the stigma. Here, then, is
the clue.
But this opens up another subject for inquiry which is A problem
discussed with some detail in the next chapter, namely, the Si dUP
abortion of ovules and the failure of fertilised ovules or questions re-
lating to the
of young seeds. Much depends in the history of the fruit abortion of
on whether the original pollination of the stigma resulted the failure
in the fertilisation of the ovules, or merely served to stimulate of seeds -
the growth of the fruit. In the first event there would be
produced a normally seeded fruit, but in the second event
only a seedless one. It is, however, the partial failure of
the ovules or seeds that will afford the most suggestive
materials for study. If some of the ovules only are fertilised,
important alterations in the form of the fruit may result ; but
the character of the change in shape will be determined by
the situation of the aborted ovules, whether at the extremities
of the fruit, or in the midst of the other ovules. Changes
in shape much less marked will occur, if the fertilised ovules
or young seeds fail early in their development. If the seed
fails at a later stage in its growth, but little effect is produced
on the fruit.
342 STUDIES IN SEEDS AND FRUITS
SUMMARY
(1) The relation between the number of seeds and the weight of
the fruit, more especially for legumes and capsules, is then investigated,
increase of size being connoted by increase of weight. In this connec-
tion the question is raised as to the stage in which the fruit offers the
best materials for such a study, whether as a moist, mature living fruit
on the plant, or as a dried fruit of the herbarium. The answer supplied
is that dried-up fruits are only of service when referred to the living
condition, since a fruit with living pericarp and actively functioning
seeds cannot be compared with one where the fruit-case is dried up
and dead, and the seeds are in a state of suspended vitality. The
comparison can only be made with dried fruits by reconstituting the
living condition.
(2) To determine this relation, however, we are often compelled
by the whip of necessity to appeal to the dry fruit ; and the author
tabulates the results of a large number of observations on dried as well
as on moist fruits.
(3) Summing up the indications of the influence of the number of
seeds on the proportion of parts in capsules, like those of Msculus^ Canna^
and Iris, he finds that the fruit, in response to the increase in the number
of seeds, whilst becoming larger and heavier, acquires a relatively lighter
pericarp. The legume, as typified by the pods of Albizzta Lebbek and
Leucfsna glauca^ on which extensive observations were made, follows
the principle of the capsule in few-seeded pods. However, in many-
seeded pods, as the seeds increase in number and the fruit increases
in length and weight, the legume preserves a fairly constant relation
between the pericarp and the seeds.
(4) The indications afforded by other legumes often give no very
definite results. This is due in part to the insufficiency of the
materials, but partly also to the influence of some disturbing cause
which specially affects small pods with few seeds, like those of Abrus
and UleX) and seems to make each plant a law to itself with regard
to the size and weight of the legume and the number of the seeds.
This influence is apt to upset all small sets of observations.
(5) It is in the abortion of ovules and failure of seeds that the
cause of this disturbing influence is to be found j and it is pointed out
that the legume would be more likely to be affected than the capsule in
this respect, since its growth is mainly in one dimension, while with
the capsule the growth is tangential rather than linear.
(6) As regards the alterations in the average weight of a seed as
the seeds increase in number and the fruit increases in size and weight,
the indications for the legume are that the seed's weight is but little
SEED-NUMBER AND FRUIT-SIZE 343
changed. For capsules the results obtained vary. Thus, with Iris, we
find that as the fruit increases in size and the seeds in number, the
seeds add to their weight and size, whilst with Canna they remain
unchanged. But when a capsule matures only one or two large seeds,
as with the Horse-chestnut (/sculus\ the seeds of the double-seeded
fruits are smaller and lighter than those of the single-seeded capsules.
(7) However, the study of the relation between the number and
size of seeds and the proportions of the fruit opens up a difficult
problem. Questions concerned with the variation in the number of
seeds in the same plant at once present themselves, and these cannot
be answered without an inquiry into the abortion of ovules and the
failure of young seeds. Much depends in the history of the fruit
on whether the original pollination of the stigma resulted in the fertilis-
ation of the ovules or merely served to stimulate the growth of the
pericarp. These matters are dealt with in the succeeding chapter.
CHAPTER XVI
THE ABORTION OF OVULES AND THE FAILURE OF SEEDS
The history I FIRST took up this subject quite accidentally in Tobago
vestigation whilst determining the proportional weight of the pericarp in
the dry beaded pods of Erythrina corallodendron. Since the
pronounced moniliform habit presented a disturbing influence,
I was led on to examine its nature, and thus the inquiry
commenced. A few weeks afterwards I made a detailed
investigation in Grenada of the failure of ovules in the dry
legumes of Albizzia Lebbek, and the inquiry developed. The
investigations were continued in England and subsequently
in Turks Islands. From the beginning my usual plan of
following indications was adopted, forming crude hypotheses
as I went along and dropping them as soon as they had lost
their usefulness. Many points of course remain undetermined,
and the contents of the present chapter can only be offered as
a contribution to the study of a difficult but highly interesting
subject.
Each fruit examined told its own story in its own way and
threw new light on some point of the subject. Thus, after I
had first learned from the legumes of Vicia that all the ovules
begin to respond to the fertilisation of the ovary, the capsules
of Primula gave the same testimony, but in a different fashion,
and further elucidated the matter. The pods of Albizzia and
the capsules of Iris and Allium afforded valuable data relating to
the influence of the early failure of ovules and of very young
seeds on the form of the fruit, the first named giving me the
344
THE ABORTION OF OVULES 345
hint that in the form of a fruit we have the history of the
ovule rather than of the seed.
Regarding the beading of legumes many fruits supplied
evidence both direct and indirect. Not only was special
appeal made to characteristic moniliform pods like those of
Sophora and Erythrina and to the less marked, though normal,
contractions of the legumes of Albizxia, but help was also
received from legumes like those of Poinciana regia^ where the
contraction of the pod is the exception and not the rule, and
from pods like those of Vicia and Ulex, where the symmetry
of the fruit is not affected by the failure of ovules and of very
young seeds. The indications again of fruits of other types,
like those of Iris, gave valuable data in this connection.
Scarcely a fruit examined failed to assist in the elucidation of
the problem. One of the earliest notes in my journal relating
to this subject was to the effect that there was evidently a very
early stage of ovule-abortion in the case of pods of Erythrina
corallodendron which expressed itself in the narrowest constric-
tions of the fruit, but left no trace of the ovule itself. This
has served to lighten up the background of the inquiry from
the commencement to the end.
I made a special study of the legumes of Vicia sativa and The failure
V. septum as concerns the abortion of ovules and the failure viSa^ativa
of young seeds. In the first case the legumes are long and "* d jum
narrow. In the second case they are short and relatively
broad. The pods of Vicia sativa average 43 or 44 millimetres
in length and about 5 millimetres in breadth, and possess as
a rule eleven mature seeds and one aborted ovule or un-
developed seed. The pods of Vicia sepium average about 3 1
millimetres in length (range 25 to 36 millimetres) and 6
millimetres in breadth, four or five seeds being usually
matured. In both species the average number of ovules in
the flower is about the same, namely, twelve, the range being
ten to sixteen in both plants.
With both species all the ovules begin to enlarge and to
turn green after fertilisation of the ovary. At first about 0-3
346 STUDIES IN SEEDS AND FRUITS
millimetre in size, they all attain a size rather less than a
millimetre. It is after this stage that the differences between
the two fruits are displayed, and in describing them I will make
use of my average results. In the case of Vicia septum four of
the original twelve ovules now begin to fail and shrivel, the
rest proceeding with their growth until about 1*5 millimetre
across, when three more fail, and ultimately only five become
mature seeds. On the other hand, with Vicia sativa nearly all
the twelve ovules give rise to mature seeds, only one as a rule
failing either in the early or later stage above described. I
may add that such a study should be made on moist green
pods in different stages, since the dry fruit could tell us but
little of the history of the ovules.
Now this conspicuous difference in the history of the ovules
is associated with considerable contrast in the growth of the
pods, the pod of Vicia sativa, where nearly all the ovules form
mature seeds, becoming long and narrow, and that of Vicia
septum, where many of the ovules fail, becoming short and
broad, so that the ripe fruits differ greatly in appearance. At
first sight one would be inclined to connect the shorter pod of
Vicia sepium with the greater failure of the ovules, since in
both species the original number of ovules is the same. But
on closer investigation we find that the contrast in length
cannot be so easily explained. In the first place, the ripe pod
of Vicia sepium is but partially filled by its seeds, whilst that of
V. sativa is nearly or completely filled. If the pod of the first
named had been quite full of seed, the argument would have
had some cogency ; but as it happens, large unfilled spaces occur
at the two ends of the seed-cavity due to the failure of the
ovules chiefly in those situations. We thus get an indication
of the independence of the size of the pod as far as concerns
the number of seeds.
From this it would follow that the same dimensions of the
legume are in the main retained in the few-seeded and in the
many-seeded pods of Vicia sepium. Further inquiry indeed
shows that this is in a general sense the case, such differences
THE ABORTION OF OVULES 347
as occur indicating only a slight increase in length of the pod
as a result of a great- increase in the number of seeds, and
affording but scant basis on which to found an explanation
of the differences in length between the pods of these two
species. Thus the rule which we would apply to explain
the differences between the two species largely fails when we
apply it to the individuals of one of them ; and we are
accordingly debarred from using this argument in explaining
the fact that the long pod of Vida saliva has many seeds
and few failures and the short pod of F. septum many failures
and few seeds.
Using legumes of the same set of plants of Vida sepium
and selecting a few at random, 1 found that a pod where all the
twelve ovules had developed into mature seeds, a very rare
event, had the same length as a pod where only five seeds had
matured. So again a four-seeded pod and a nine-seeded pod
had the same dimensions. In the aggregate, however, there
is a tendency in the pod to increase its length as the seeds
increase in number ; but it is quite insufficient to explain the
difference in length between the pods of these two plants.
Thus ten pods of Vida sepium containing four or five seeds
had an average length in the dry state of 30 millimetres, whilst
five pods containing from seven to twelve seeds had an average,
length of 35 millimetres. Here the doubling of the number
of seeds only resulted in the increase of the pod's length by
one-sixth.
There are two other points to notice in connection with
the legumes of these two species of Vida. In the first place,
it will have been remarked that the aborted ovules, or more
correctly speaking the seed-failures, are complemental to the
matured seeds, the two going to make up the complete set of
the original ovules. This is well brought out in the results
tabulated below ; and on referring to the general table for
ovular abortion in fruits given later in this chapter, it will
be seen that this principle is characteristic of fruits of all
kinds.
348
STUDIES IN SEEDS AND FRUITS
In the next place, there is as a rule no " beading " to be
observed in these fruits of Vicia^ a character which is associated
in moniliform pods with failure of the ovules. This is in
part due to the fact that the failure of the growing ovule or
young seed usually takes place in these pods at the extremities
of the seed-cavity and not in the middle. But this only partly
explains the absence of contractions, since much also depends
on the structure of the pod itself.
TABLE SHOWING HOW THE ABORTED OVULES AND THE SMALL IMPERFECT
SEEDS OF VICIA SEPIUM COMBINE WITH THE MATURED SEEDS TO
FORM THE ORIGINAL COMPLEMENT OF THE OVULES (12).
(Twenty-four pods were examined. In a few cases the aborted ovules and imperfect
seeds are differentiated, the results being given in the last two columns. )
Mature seeds.
Aborted ovules
and imperfect
half-sized seeds.
Total.
Aborted ovules.
Imperfect half-
sized seeds.
2
10
IZ
Z
10
IZ
3
8
ii
6
z
3
8
ii
3
5
3
7
10
4
9
'3
4
9
13
4
9
"3
4
7
ii
4
7
ii
4
7
ii
4
6
10
5
7
IZ
5
7
IZ
4
3
5
7
IZ
3
4
5
6
II
3
3
6
7
'3
4
3
6
7
'3
3
4
6
6
12
4
2
7
4
II
8
4
IZ
9
3
IZ
ii
II
12
IZ
Av. 1 1 7
All the ovules begin to enlarge and to turn green after the fertilisation of the ovary.
Some of them fail before they attain a size of a millimetre and are termed aborted ovules.
Others proceed further with their growth, but fail when about half-size ( i "5 millimetre).
The original size of the ovule is about o'j millimetre, their number averaging twelve.
THE ABORTION OF OVULES
349
TABLE SHOWING HOW THE OVULES THAT FAIL TO PRODUCE SEEDS IN
THE CASE OF VlCIA SATIVA COMBINE WITH THE MATURED SEEDS TO
FORM THE ORIGINAL COMPLEMENT (12) OF THE OVULES BEFORE
FERTILISATION OF THE OVARY.
(Ten pods were examined. All the remarks on the size, behaviour, and original
number of the ovules of Vicia septum, as given at the foot of the preceding table, here
apply.)
Aborted ovules
Mature seeds.
and imperfect
half-sized seeds.
Total.
ii
ii
ii
i
12
10
i
II
ii
i
12
9
i
IO
IZ
2
H
ii
2
13
10
3
13
12
I
'3
II
I
12
Av. 1 2 'i
To no fruits have I paid more attention to the relation The failure
between the failure of the ovules and the form and size of the
fruit than to the legumes of Albizzia Lebbek. All my materials
were obtained from one tree in Grenada ; but the observations
were restricted on account of the season to the dry pods.
These legumes well illustrate the commencement of the
moniliform habit, but the contraction is rarely so marked as
to merit that epithet.
The first thing to notice is the relation between the
number of seeds and the length of the fruit. It will be
observed from the results tabulated below that there is a
progressive increase in the pod's length from the single-seeded
to the twelve-seeded fruit ; but, as also indicated in the pods
of Vicia sepium, the increase in length is relatively small, since
the twelve-seeded legume is only about twice the length of the
single-seeded fruit. Thus we obtain here another indication
of the independent growth of the fruit-case as regards the
seeds.
35
STUDIES IN SEEDS AND FRUITS
TABLE ILLUSTRATING IN THE CASE OF THE DRY LEGUMES OF ALBIZZIA
LEBBEK THE RELATION BETWEEN THE NUMBER OF SEEDS AND THE
LENGTH OF THE POD.
Number of
seeds in a pod.
Number of pods
examined.
Average length of a pod.
Range of length
in inches.
i
10
142 millimetres
5 '6 inches
4-9- 6-5
i
14
1 80
7'i
6-3- 8-5
3
3
193
7-6
6-3- 87
4
14 ziS
8-6
7'2- 9 '8
5
*3
224
8-8
7'o-io'3
6
10 236
9'3
7-6-10-5
7
8 251
9 '9
8-5-11-3
8
8 262
10-3
9 P o-n'4
9
10 I 254
IO'O
8'4-n'i
10
ii
290
11-4
IO'O-I2'5
ii
8 282
ii'i
IO'I-I2'3
IZ
10 295
1 1 -6
10-8-13-2
These data are included in a table in Chapter XV. , where the relations between the
length and weight of the pod and the number of seeds are compared. The slight
difference in three of the results is due to an additional pod being employed in the above
table.
But it is around the early abortion of the ovules after the
fertilisation of the ovary that our interest in the fruits of
Albizzia Lebbek chiefly centres. With this feature in the
history of these legumes are associated the contractions in the
pod's width, which frequently give a fantastic shape to the
fruit, as illustrated in the figures outlined in a later page.
The legumes readily lend themselves to such an inquiry.
The aborted ovules are conspicuous in the dry pod and
present themselves as little black bodies 0*2 millimetre in size,
attached to the end of the funicles, which are usually well
preserved. The term aborted ovule is here applied, as in Vida^
to ovules that fail soon after the fertilisation of the ovary.
Ovules that did not abort in this early stage as a rule advanced
sufficiently far in their growth to be designated seeds. It
will be subsequently shown that the failure of seeds advanced
in growth has little or no influence on the fruit. As the
result of a large number of observations the following infer-
ences were formed.
THE ABORTION OF OVULES 351
In the first place, the complemental value of the aborted
ovules with regard to the seeds is to be noticed. I had no
opportunity of examining the flowers of this tree ; but it is
evident from what follows that, as in Vicia^ the ovules average
about twelve in number. So we find that whilst the one-
seeded pods have usually about eleven aborted ovules, the
twelve-seeded pods have none. With the intermediate pods
we accordingly find the same relation. Thus a four-seeded
pod displays about eight ovules and an eight-seeded pod about
four ovules. This complemental relation is well displayed
in the following table.
TABLE SHOWING THE COMPLEMENTAL RELATION IN THE CASE OF
TWENTY-TWO LEGUMES OF ALBIZZIA LEBBEK BETWEEN THE NUMBER
OP SEEDS AND THE OVULES THAT FAIL.
(See previous remarks for further explanation.)
Number of
seeds.
Aborted
ovules.
Full
complement.
Number of
seeds.
Aborted
ovules.
Full
complement.
i
ii
12
5
8
'3
i
ii
12
5
7
12
i
ii
12
6
7
'3
2
10
12
7
4
ii
2
9
II
8
4
12
2
8
10
8
4
12
3
10
'3
9
3
12
3
9
12
10
2
12
4
9
13
12
12
4
8
12
12
o
12
4
S
12
'3
'3
Pods with thirteen seeds are rare, probably not i per cent, in frequency. Those with
two to four seeds are most numerous, the single-seeded pods being infrequent.
Another important result was elicited by these observa-
tions, namely, that the shape of the pod of Albizzia Lebbek is
not affected by the failure of a seed when it is well advanced
in growth. Thus if a seed fails in the body of the pod when
it is only one-third or one-half of the mature size, no narrow-
ing of the fruit occurs. The form of the pod thus gives an
epitome of the history of the ovules, but not of the seed.
(I am assuming here that, as in Vicia^ Ulex y etc., all the
352 STUDIES IN SEEDS AND FRUITS
ovules share at first in the results of the fertilisation of
the ovary ; and it is to those that fail early that the epithet
of " aborted " is applied.) It is the early failure of the
ovule that alone determines the contraction of the legume,
and it is the number of such contiguous ovules that deter-
mines its amount.
The external form of the legume of Albi-zzia Lebbek there-
fore at once gives a clue as to the number of ovules that have
aborted early and the number that have advanced to the seed-
stage ; but it tells us nothing of whether the seed inside is
fully formed or only half or a third of the normal size, the
opening of the pod being required for that purpose. The
form of the pod, therefore, depends on the fate of the ovules
in an early stage of their history after the fertilisation of the
ovary. After that is determined the ultimate form of the pod
is fixed, and is not affected even if all the seeds fail before
attaining half their normal size.
With the early failure of the ovules are connected, as before
remarked, the contractions of the pod, which may be so slight
as merely to give a sinuous margin to the fruit, or so marked
as to produce almost a beaded shape. The moniliform
tendency is displayed when the failure takes place in the body
of the fruit. When the ovules abort at the ends the pod
acquires tapering extremities. Now, as respects the narrowing
of the body of the fruit, I find that the extent of the contraction
depends on the number of contiguous ovules that fail. Thus
a typical many-seeded pod, 35 millimetres broad in the seeded
portion, has its width reduced to about 30 millimetres where a
single ovule fails, to about 25 millimetres where two con-
tiguous ovules abort, and to about 12 millimetres where three
or four ovules fail. As a rule, when the space between the
seeds is 1 2 to 1 5 millimetres broad there is no aborted ovule.
When the inter-seminal space amounts to from 20 to 22
millimetres in width there is a single aborted ovule. When it is
30 to 35 millimetres there are two contiguous aborted ovules ;
when 45 to 50 millimetres, three contiguous ovules, and so on.
THE ABORTION OF OVULES 353
The following outline-figures will serve to illustrate the fore-
going remarks.
ALBIZZIA LEBBEK
C 9 inches.
A 7J inches.
These figures illustrate the relation between the contractions of the
legumes and the failure of ovules shortly after the fertilisation of the ovary,
the contraction being greatest when contiguous ovules abort, and least
when only one fails.
All the figures are greatly reduced, but on the same scale. The seeds
are indicated by large black spots, and the ovules by small black ones.
In these diagrams it is assumed that the pod can be seen through. The
seeds and ovules are, of course, arranged alternately on the two valves.
Many of the features of the legumes of Albizzia Lebbek
are exhibited by the irregularly moniliform pods of Cytisus Cytisus
Laburnum, though here the ovules do not fail early but proceed a urn
23
354
STUDIES IN SEEDS AND FRUITS
Ulez
europaeus.
Eotada
polystachya.
Guilandina
bonduceila.
a little with their growth and abort as young seeds. When
all the ten ovules form mature seeds, or advance considerably
in growth, the pod is regular in form and displays no con-
strictions ; but more often three or four of the seeds fail in
a very early stage, and when contiguous produce a marked
constriction in the mature fruit. The club-shaped single-
seeded pods, where all the ovules fail except one near the
distal end, are very remarkable.
Reserving my treatment of beaded legumes for a later
page, it may be here added that important data relating to this
subject are supplied by the legumes of Ulex europaeus and
Entada polystachya. The examination of the Ulex pods brought
out the fact that early abortion of the ovules never even
provokes a tendency to moniliform contraction, and that the
form of the pod, fixed soon after the fertilisation of the ovary,
remains unaffected by the early failure of the ovules. This no
doubt results from the structural characters of the pericarp.
The legumes of Entada polystachya also gave their indica-
tions. Here there is no early failure of the ovules after the
fertilisation of the ovary ; but all advance considerably in
growth, and when failure occurs it is the young seed about a
fourth of the normal size that aborts. Here the fruit consists
of a series of joints each containing a single seed and held
together in the dry state by the " replum," a stout stem-like
border that would of itself prevent any constriction of the pod.
The usual absence not only of a seed but of any trace of an
ovule in the two terminal joints leads one back to an earlier
condition of things, when additional ovules existed that are
now doubtless only represented by rudiments in the ovary,
and disappear altogether in the fruit.
The behaviour of legumes with one or two seeds is well
represented by the fruits of Guilandina bonducella. The ovary
here possesses two ovules, and it would seem that as a rule
half of the pods mature one seed and the rest two seeds. In
the first case the second seed usually attains a diameter of 4 or
5 millimetres before aborting, the mature size being about 25
THE ABORTION OF OVULES 355
millimetres. We can thus perceive, as explained with regard
to Albizzia pods, why no effect is produced on the form of the
fruit by the failure of one of the seeds. Had the ovule failed
in an early stage the effect might have been noticeable. But
even then, as in the case of Ulex pods, it is probable that there
would have been no constriction in the pod's width, a result
due to the structure of the pod itself.
Capsular fruits now claim our attention ; and it may be The failure
said of them, as of the legumes, that the mature seeds, the ^p^SS" 1
young seeds that fail before they attain any size, and the
ovules that abort early, make up the full complement of the
ovules in the flower. This is well brought out in the average
results given in the table preceding the summary of this
chapter, and one need scarcely labour the point here. They
all behave, for instance, like the fruits of Arenaria peploides.
The primal complement of twelve ovules in this case can
almost always be recognised in the fruit, whether the fruit only
contains five or six seeds or as many as ten, the failures making
up the balance. All the ovules of the unfertilised ovary can
be thus accounted for. They are potentially seeds from the
beginning. The occurrence of rudiments of ovules in the
flower raises quite another question, which will be dealt with in
a later page.
As an example of the influence of the failure of ovules on Illustrated
the form of capsules, I will first take that of Iris Pseudacorus. i^ s Pseuda-
Here there are two rows of ovules in each of the three com- corus *
partments of the fruit ; and they all begin to enlarge after the
fertilisation of the ovary. If most of the ovules in each of the
two rows mature as seeds, the seeds are closely packed and
overlap each other and are irregularly wedge-shaped ; but if
the ovules in only one of the rows become seeds, whilst those
of the other row fail, then the seeds assume a disc-like form.
Failure of some of the ovules is, however, a normal event,
and much depends on their number and on their situation.
Thus the average result given in the table at the end of the
356
STUDIES IN SEEDS AND FRUITS
chapter for a fruit possessing 120 ovules is that 80 mature
as seeds, 30 fail soon after the preliminary enlargement due
to fertilisation, and 10 fail after they have attained a fourth
or a third of the size of the normal seed. In the typical
oblong fruit 9 or 10 ovules soon abort at the bottom of each
IRIS PSEUDACORUS
Outline-figures of the capsules of Iris Pseudacorus showing
the effect on the shape of the partial failure of the ovules and
young seeds in different parts of the fruit, as described in the
text.
A = a typical regular fruit.
B = a club-shaped or bulbous fruit.
C=a fiddle-shaped fruit.
D = a curved or arcuate fruit.
compartment. The occasional early failure of nearly all th<
ovules in the lower third of the young fruit gives the mature
capsule a bulbous or club-like shape. I found such fruil
frequent in one locality. An outline-figure of one of thei
is given above. If this became the rule, the bulbous form
would become a specific constant. Should the early failure
THE ABORTION OF OVULES 357
of the ovules and of the young seeds be principally restricted
to the centre of each compartment, the fruit-walls collapse in
the middle and we get a fiddle-shaped fruit, as shown in the
figure.
Then, again, if the failure of the ovules and young seeds
takes place mainly in one loculus, whilst the seeds in the other
two for the most part develop normally, the mature fruit then
assumes a curved or arcuate shape, the concavity corresponding
to the compartment in which the failures are situated. Some-
times in arcuate fruits two loculi or compartments correspond
to the concave side ; and then it will be found that seeds are
lacking in the centre of each of the two loculi concerned. If
the third compartment had been similarly affected, a fiddle-
shaped fruit would have been produced. However, the
essential feature of the arcuate type of fruit is a full set of
seeds on the convex side, associated with extensive abortion
or failure of the ovules and very young seeds on the concave
side. Such are some of the commoner types of deformation
of these capsules ; but lesser irregularities arising from the
same cause are numerous.
Irregular forms of the capsule, such as are frequent with
Iris PseudacoruS) are not so common with Iris fcetidissima. The Iris foetid-
fruits of the last named are useful in illustrating the fact that
there is always a variation in the original number of ovules
in each compartment of capsules of this type. The variation
is not large, but it is sufficient to indicate a possible initial
disturbing influence that would affect the symmetry of the
plurilocular capsule. There are here appended the results
obtained from four flowers of Iris fcetidissima for the three
loculi.
A
B
C
D
1 8 -j- 1 8 + 20 ovules
20 + 22 4- 22
17 + 17 + 21
16 + 16 + 18
Respecting the distribution of aborted ovules in the several
compartments of a plurilocular capsule, 1 obtained the following
358 STUDIES IN SEEDS AND FRUITS
Sciiia data for Scilla nutans. Here each of the three loculi of the
ovary contain from ten to twelve ovules, and each of the three
compartments of the fruit on the average seven or eight seeds.
As a rule early failure of the ovules and of the young seeds
takes place with fair uniformity in the different compartments.
Fruits displaying such variations in the number of seeds in each
of the loculi as five, eight, seven, were frequent ; whilst those
where the divergence was greater, such as three, eight, six,
were infrequent. Out of a large number of fruits examined,
none ever displayed a complete failure of the seeds in one
compartment.
Primula I will now take the capsules of Primula veris, in which
most of the abortions of ovules and of the failures of young
seeds take place around the base of the placental column. A
typical ovary contains on the average about ninety white ovules.
Of these all at first respond to the stimulus of the pollen,
but only about sixty mature as seeds. Of the remaining ovules
about twenty-two abort early when still uncoloured, whilst the
rest (eight) turn green and advance a little in their growth before
they too fail. Thus in Primula capsules we have a colour-
indication which enables us to distinguish between the early
failures of the ovules and the later failures of the young
seeds, the first white, the second green like the growing seeds.
Allium In Allium ursinum we have a three-celled ovary, each cell
ursinum. . i xtr i i 11 i
containing two ovules. Or the six ovules only three on the
average mature as seeds, and often only two or even only one.
In all cases the ovules that abort early and the seeds that soon
fail combine with the mature seeds to make up the original
complement of six ovules in the flower. The ultimate form
of the fruit is, as might be expected, very variable, and
irregularities almost appear to be the rule. Regular fruits
have a seed in each cell ; but it is not uncommon to find
two seeds in one cell, one seed in another, and none in the
third, and then the shape is very irregular. However, all
the ovules begin to enlarge after the fertilising process and
at the same time all the cells enlarge as well ; but when the
THE ABORTION OF OVULES 359
two ovules in a cell fail early, the growth of the cell does not
proceed far. Here it is evident that the initial growth of
the fruit is determined by the fertilising process, but its later
growth depends on the seed.
In Aquikgia each carpel contains on the average thirty ovules, Aquilegia.
of which twenty-five mature as seeds, four abort early, and one
fails after proceeding a little further in its growth. Most of the
aborted ovules usually occur in a clump at the lower end of the
follicle. This may be connected with the fact that in the
flower the ovules at the base of each carpel are exposed by
the gaping of the carpellary walls, and remain exposed during
much of the ripening of the fruit.
The tremendous waste of ovules, or rather of young seeds, Ravenala
A
in the sub-drupaceous capsule of Ravenala madagascariemis has SUienS&T
already been alluded to in Chapter XIII. in connection with
the dehiscence of the fruits. Of the plants with many-ovuled
flowers included in the table near the close of this chapter
there is not one that comes near Ravenala in this respect, five-
sixths of the ovules at a very moderate computation failing to
mature as seeds. It would seem, however, that nearly all of
them first reach an early stage of seed-growth. One cannot
help thinking that this large sacrifice of seeds is due to the
great pressure exercised by the growing seeds upon each other
within the stony, and for a long time unyielding, walls of the
endocarp. When dehiscence at length occurs, the fruit-cavity
is seen to be full of aborted seeds, 2 to 5 millimetres in size,
with only a few large matured seeds.
Although the beading of legumes is well marked in some The beading
genera, as in Erythrina and Sophora, a slight tendency to the
moniliform type is frequently displayed in other leguminous
genera with long pods, such as Faba, Genista, Phaseolus,
Poinciana, etc. Though abnormal in such cases, it is due to
the same influences that operate in the typical moniliform pod,
namely, the early abortion of ovules and the early failure of
seeds in the body of the fruit. In some other cases, as in those
of the Laburnum and of Albizzia^ the tendency is pronounced ;
Poinciana
regia.
Erythrina
corallo-
dendron.
360 STUDIES IN SEEDS AND FRUITS
but here the structural characters of the fruit act as final checks.
In short broad pods like those of Ulex there is no constriction
as a result of the failure of the ovules. The same remark
applies to those of Picia ; but here the absence of any contrac-
tion of the legume is due chiefly to the failures occurring
usually at the ends of the fruit. When several ovules and
young seeds fail at the ends of a legume, we have tapering
extremities. Such failures do not necessarily lead to shorten-
ing of a legume. An unusually short fruit is associated with
an unusually small number of ovules in the flower.
Length in a legume is one of the pre-disposing causes ;
and in such a case even a dense ligneous texture, as in Poinciana
regia^ may not be sufficient to suppress the tendency. Here
the failure of seeds that have advanced in their growth seems
to have but little influence ; but if a few contiguous ovules
abort soon after fertilisation, or if a few contiguous seeds fail
in a very early stage, a slight constriction of the pod is produced,
the place of the seeds being occupied by ligneous material.
Thus in a legume of Poinciana regia^ where the space of four
seeds was thus filled up, the width of the legume was reduced
from 48 to 40 millimetres.
Coming to the typical moniliform legumes, I will begin with
those of Erythrina corallodendron^ which first led me to undertake
this inquiry. Here there is a distinct relation between the
beading of the pod and the failure of very young seeds ; but
this is not the whole of the matter, since the narrowest con-
strictions show no trace either of ovule or of seed. Here it
may be that we have an indication of the influence of rudi-
ments of ovules in the flower which disappear altogether in the
fruit. In the accompanying diagram I have represented a
typical seven-seeded dry pod about 115 millimetres long. At
A, E, and F the constrictions are very narrow, 2 millimetres or
less, and there is no trace of either seed or ovule. The other
constrictions (B, C, D) are broader (2*5 millimetres to 3 milli-
metres), and here aborted seeds 11*5 millimetres long occur, the
length of the constricted portion being regulated by the number
THE ABORTION OF OVULES 361
of contiguous seeds that have failed. These seeds when they
aborted in the living fruit could not have been more than a
sixth of the normal length, and when the failure took place the
pod was probably about a third of its length when mature.
The above results of my examination of the pods of Erythrina
corallodendron would lead one to infer that the narrowest con-
strictions, where not a trace of ovule or seed is to be recognised,
are concerned with a much earlier stage of abortion, and this is
also indicated by the terminal pointed beak. One may suppose
that there were rudiments of ovules in the flower that were
unable to respond to the fertilisation of the ovary, thus restrain-
ing the response of the ovary in those places to the stimulus
of fertilisation. In this connection we have to bear in mind
that the fruit as well as the seed is a product of pollination.
The flower in the case of the seven-seeded pod above
described probably displayed thirteen ovules in its ovary,
which I imagine would be typical for the species. Doubtless
there were the rudiments of six or seven other ovules in the
ovary, taking the beak of the fruit into consideration ; and the
primal complement of ovules was therefore probably twenty,
though the other seven ovules need never have passed beyond
the primordial stage. In other words, to adopt Dr Goebel's
standpoint with regard to rudimentary organs in plants, the
assumption of a primal complement of ovules larger than that
of existing flowers does not require us to assume that all of
them " functioned " as mature ovules. Such were some of the
speculations that passed through my mind when I examined
the first moniliform pods ; and they have been exceedingly
helpful to me ever since.
The moniliform pods of Sophora tomentosa were examined Sophora
i i -11 tomentosa.
in the moist condition. A typical legume contains six or seven
seeds separated from each other by narrow necks which often
enclose shrivelled aborted seeds i to 3 millimetres long, the
length of the neck depending on the number of aborted seeds,
as indicated in the accompanying figure. We seem to be only
concerned here with the failure of young seeds ; but still earlier
362 STUDIES IN SEEDS AND FRUITS
failures are indicated when seeds, though actually in contact, are
separated in a sense by a slight contraction of the pod, suggest-
ing, as I would suppose, the existence of a rudimentary ovule in
the flower which has disappeared in the fruit. The constriction
of legumes is so generally associated with the early failure of
ERYTHRINA
CORALLODENDRON
SOPHORA
TOMENTOSA
Diagram of a seven-seeded dry
pod, showing also six aborted
seeds in the broader necks :
drawn to a true scale.
Diagram of a portion of a green
pod, showing the effect of failure
of the seeds on the form of the
fruit. The pod has not begun to
dry, and the seeds are soft and
large : drawn to a true scale.
ovules and young seeds that one would be scarcely justified in
regarding a slight contraction as belonging to another order oi
things. Single-seeded fruits are spindle-shaped and contain
the remains of at least six or eight seeds that failed in an early
stage of their growth. When examining these pods I had no
opportunity of inspecting the flowers ; but I should imagine
that the average ovular complement would be twenty, though
THE ABORTION OF OVULES 363
liable to considerable variation. The number of seeds in a
pod varies from one to ten.
The development of the seedless fruit has a most important The indica-
bearing on the relation between the form of many fruits and ^dless 16
the failure of the ovule. The germination of the pollen-tube, fruit
writes Dr Jost in his Lectures on Plant Physiology (English
edition, 1907, p. 370), has an exciting influence on the develop-
ment of the fruit, so that fruits may be formed where de-
generate ovules fail to become seeds. Again, Dr Pfeffer writes
that the penetration of pollen-tubes may act as a stimulus to
growth of fruits without any fertilising influence being exercised
(Physiology of Plants, ii. 173). We have here a means of
explaining some of the curious forms of fruits. But much
will depend on whether the ovules habitually fail in the same
part of the young fruit, or whether their failure is occasional
and not restricted to one situation. In the first case we have
a persistent effect produced on the fruit's shape which requires
a specific or a generic value, as in Anemone. In the second we
have inconstant variation of the fruit's form, such as I have
described in the instance of Iris Pseudacorus.
It would, however, be rash with the scanty data at my
disposal to push this view very far. Yet the ovules that fail
in a Primula or an Iris capsule appear to be in quite a different
category from the ovules that fail in the fruits of the Oak or
of the Coco-palm. In the first case it would seem that the
ovules were actually fertilised and afterwards aborted. In the
second case it would appear that the ovules were incapable of
being fertilised, since they persistently fail. Lord Avebury
would regard such persistently functionless ovules as carrying The
, r i i ii -L functionless
us back to the time when, in the ancestors or the plant, all the ovu i e>
ovules developed into seeds (Seedlings, Internat. Sci. Ser., pp.
241 and 243). Professor Bower holds a similar view with
reference to the abortive ovules in the beak of a fruit of
Anemone nemorosa, regarding them as "the imperfect repre-
sentatives of a plurality of ovules in the ancestry" (The Origin
of a Land-Flora, 1908, p. 127). It should, however, be pointed
364 STUDIES IN SEEDS AND FRUITS
out that this would not follow if we accept the standpoint
taken by Dr Goebel in his Qrganography of Plants (i. 61), that
functionless organs in plants are not necessarily the vestiges
of former completely developed ones, and that many more
primordia are laid down than become functional.
Many points remain to be determined before we can safely
generalise in these matters. It is of importance, for instance,
to ascertain by microscopical examination why, with the same
complement of about twelve ovules in the flower, ten or eleven
seeds are matured in Vicia sativa and only half that number in
Vicia sepium. Then, again, it would be necessary to learn if
the ovules that fail in the acorn, coco-nut, and similar fruits,
have the same microscopical characters as the ovules that com-
plete their development.
Some indica- Nearly all the data included in the following table are from
following my own observations, with the chief exception of those relating
table. to Convallaria, which are taken from Lord Avebury's book on
seedlings. Although with many-ovuled flowers there is great
variation as to the number of ovules that mature as seeds, as
many as 80 or 90 per cent, failing in Ravenala and as few as
17 per cent, in Aquilegia and Lychnis^ yet a rough average
shapes itself for several of the capsules here dealt with. Thus
with Iris, Primula^ Scilla^ Stellaria, and Arenaria about two-thirds
of the ovules mature as seeds, and of the remainder the greater
number (about 25 per cent, of the ovular complement) abort
soon after fertilisation, whilst the residue advance a little in
their growth and fail as young seeds. With leguminous
plants the same rule prevails, though the data are insufficient
for a numerical statement. Here also a large proportion of
the ovules develop into seeds, but a considerable number fail,
and of the failures most are concerned with the abortion of
the ovule soon after fertilisation.
In nearly every case the number of the ovules in the flower
has been directly determined ; but in the cases of Ravenala
and Opuntia it has been estimated from the total of mature
seeds and of seed-failures.
THE ABORTION OF OVULES
365
TABLE SHOWING THE AVERAGE PROPORTION OF FAILURES OF SEEDS.
(See below for explanation.)
Range
of
number
of
ovules
in a
flower.
Average
number
of
ovules
in a
flower.
Seeds
matured.
Failures
of ovules
and
young
seeds.
A.
Failures
of
ovules.
B.
Failures
of
young
seeds.
Number.
Percentage.
1
3
40
26
3
ii
4
4
5
3
6
7
i
7
5
V
1
V
&
33
44
33
33
36
34
33
5
5
58
8
58
'7
1
3
18
22
8
- Percentage.
Number.
&
S
V
a
V
8
9
8
Iris Pseudacorus, C.
,, foetidissima, C.
Primula veris, C. .
Scilla nutans, C. .
Stellaria Holostea, C.
Arenaria peploides, C.
Entada polystachya, L. .
Allium ursinum, C.
Ulex europseus, L. .
Vicia sepium, L.
,, sativa, L.
Albizzia Lebbek, L.
Lychnis diurna, C. .
Silene maritima, C.
Ravenala madagascari-
ensis, C.
Quercus Robur, N.
^Esculus Hippocastanum,
C.
Convallaria, B.
Opuntia Tuna, B. .
Prunus communis, D.
Aquilegia (a single carpel)
90-160
50-65
70-100
25-38
9-12
10-13
6*
10-13
10-15
10-15
10-13
100-180
6
6
6
2
23-35
120
60
90
33
ii
12
'5
6
12
12
12
12
300
150
60
6
6
6
IOO
2
30
80
34
60
22
7
8
10
3
6
5
ii
5
250
67
56
67
67
64
66
67
5
5
42
92
42
83
10
8
8
3
2
2
4
4
33
33
33
2
5
i
2
3
33
l?
1 7
7
58
10
i
2
I
80
I
25
17
17
33
17
80
83
5
5
4
5
20
I
5
83
83
67
83
20
5
83
5
83
i
17
4
'3
i
4
The percentage results given represent the proportion of the average number of
ovules, as stated in the second column.
The data given in the last two columns, A and B, distinguish between the failures of
ovules and the failures of young seeds.
The fruit-type is indicated by the capital letter after the plant-name : B, berry ; C,
capsule ; D, drupe ; L, legume ; N, nut.
SUMMARY
(i) The subject of the failure of ovules and its influence on the
form of the fruit was first taken up in connection with moniliform
legumes, and the inquiry was extended to other fruits. Each fruit
examined told its own story, and although many points remain unde-
termined, the data obtained go to support the following conclusions.
366 STUDIES IN SEEDS AND FRUITS
(2) In the first place, all the ovules begin to respond to the fertilisa-
tion of the ovary. This is equally true when it concerns the legume,
as in Vicia and Ulex^ and when it concerns the capsule, as in Primula
and Iris.
(3) In many-ovuled flowers failure of a proportion of the ovules is
a normal occurrence after the first enlargement due to the stimulus of
fertilisation. In the case of plants with capsular fruits, it frequently
happens, as in the case of Arenaria^ Stellaria^ Primula^ Sci/Ja, and Iris,
that only two-thirds of the original complement of ovules develop into
mature seeds. Of the ovules that fail, the greater number abort soon
after fertilisation, whilst the remainder proceed a little with their
growth and fail as young seeds. The same principle applies to plants
with legumes, most of the ovules generally maturing as seeds, whilst
of the remainder the majority abort early.
(4) It is shown that all the ovules conspicuous in the flower can
be accounted for in the fruit, the complete ovular complement being
made up by the ovules that abort soon after fertilisation, the seeds
that fail in an early stage, and the seeds that proceed to maturity.
(5) It is in the legume that the influence on the form of the fruit
of the failures of ovules and young seeds is generally most evident, a
marked constriction resulting when the failures are contiguous in the
body of the fruit, the degree of constriction being determined by the
number of contiguous failures. The same principle applies to capsules,
but not usually to the same extent. Yet in fruits like those of Iris
and Allium great changes in the shape of the fruit may be thus brought
about. In both legumes and capsules, however, but little effect is
produced on the fruit's shape by the failure of seeds far advanced in
growth. The form of the fruit is determined much earlier in its
development. In a word, in the form of the fruit we have the history
of the ovule rather than of the seed.
(6) Dealing especially with beaded legumes, it is first pointed out
that abnormal constrictions of pods that are usually symmetrical, as in
Faba, Phaseo/us, and Poinciana, are due to the same influences that
operate in the moniliform pod, namely, those concerned with the early
abortion of ovules and the early failure of seeds. Even woody legumes,
such as those of Poinciana regia^ may exhibit constrictions due to the
same causes.
(7) Next come those legumes, as with Albizzia Lebbek and Cytisus
Laburnum^ where extensive failures of the ovules and young seeds
habitually occur, producing a marked tendency towards the moniliform
habit, but not sufficient to justify their being characterised as beaded
legumes.
(8) As examples of the typical moniliform legume those of Erythrina
corallodendron and of Sophora tomentosa are taken. Whilst the remains
THE ABORTION OF OVULES 367
of ovules and of young seeds are generally found in the constricted
portions, it is shown that in certain cases no such remains exist, and
it is argued that here we are concerned with only rudimentary ovules
in the flower.
(9) Special stress is laid on the important indications given by the
seedless fruit, where the fruit develops under the stimulus of pollination
but the seeds fail. In the effects of failure of the ovules and young
seeds on the fruit's shape a distinction is drawn between the constant
failure of ovules in fruits, like those of Quercus and Cocos nucifera^ and
the normal failure after fertilisation of a certain proportion of the
ovules in many-ovuled flowers, such as those of Iris and Primula. In
the one case a persistent effect is produced on the fruit, in the other
case an inconstant one.
(10) Much remains to be determined before one could safely
generalise in these matters. It will be necessary to distinguish between
the primal complement of ovules in a flower and the complement on
which the systematist bases his distinctions. Of the second all are
" functionable." Of the first many may never have passed beyond
the primordial stage and may always exist as rudiments in the flower.
Thus the carpels of Anenome are described as one-ovuled, yet the beaked
form of the fruit has received its impress from other functionless ovules
which the systematist does not recognise.
CHAPTER XVII
Inquiry
mainly
directed to
the con-
ditions of
coloration.
Not specially
adapted.
Seed-colours
in a native
garden in
Jamaica.
SEED-COLORATION
SEEDS, as is well known, display a great variety of hues,
ranging from white and pale colours to deep green, black,
brown, and red. Many seeds have a neutral or nondescript
colour, which it is not easy to describe ; but probably brown in
its numerous shades and mixtures is the most frequent. Whilst
handling seeds so much, the colours naturally attracted my
attention ; but seed-coloration involves so many points,
physical, chemical, and biological, that a general treatment of
the subject would be quite beyond my powers, and I will
therefore mainly confine my remarks to a consideration of the
conditions in which seeds acquire their colouring.
Matters relating to adaptation to means of dispersal will also
be outside the field of discussion, but for quite another reason.
The fancy is apt to detect similarity and adaptive purpose where
in its ignorance accident alone could reign ; and it is too ready
to forget that in the nature of things the whole organism is
but a mass of adaptation, not only the cell-aggregate, but the
cell itself. Adaptation to the conditions of life is the very
essence of existence ; and we are not justified in singling out
and designating as specially adaptive any character that happens
to catch the eye, whilst ignoring all the rest. Adaptation goes
without saying in this world of ours.
In the matter of seed-coloration puzzles surround us,
especially in the tropics. Thus in the cultivated patch of a
Jamaican native you may see growing side by side Canavalia,
368
SEED-COLORATION 369
ensiformis with white seeds and Canavalia gladiata with red
seeds, two plants by some considered as varieties of one species.
(This association of white with coloured seeds is found also
with our Scarlet-runner (Phaseolus multlflorus^ where, besides
the usual form with dark mottled seeds, there is a form with
white seeds.) Looking around us in this bush-garden, we
notice a great variety in the colours of the seeds, particularly
with leguminous plants, some of which have been planted for
ornamental or useful purposes, whilst others owe their
presence there to birds. Growing over a neighbouring bush
we notice Abrus precatorius, displaying in its opening pods the
familiar bright red seeds with a black spot. Forming a shade
for the young Cacao plants, we observe small trees of Erythrina
corallodendron, exhibiting in their moniliform pods seeds strik-
ingly similar in coloration to those of Abrus precatorius, though
larger in size. Amongst the shrubby growths at the borders
of the patch we see Casalpinia sepiaria, the " Wait-a-bit " of
the Jamaicans, showing dark mottled seeds in its dehiscing
pods. Single trees, such as Adenanthera pavonina and Blighia
sapida^ are scattered about, the first-named displaying in its pods
the beautiful large scarlet seeds used for necklaces, the second
being the well-known Akee, from the branches of which hang
bright red fruits, showing, as they open on the tree, shining
black seeds partly exposed in their yellow arils. Hanging from
a vine in the branches of one of these trees are the long dry
fruits of the Loofah (Luffa acutangula), with their black seeds
falling out ; whilst on a neighbouring fence we see suspended
the yellow fruits of Momordica Charantia (another cucurbitaceous
plant), which, as they open, display their seeds in bright red
soft coverings. However, when we turn to the fruit trees, the
species of Citrus and Anona, the Sapodilla (Achras Sapota\ and
the Star Apple (Chrysophyllum Cainito\ we miss the brightly
coloured seeds, and find in their place whitish or brown seeds.
If the above illustration exhibits the variety in hue of
tropical seeds, it also makes evident the difficulties attending
such inquiries, and it at the same time shows the necessity of
24
Seed-colours
that dis-
appear
before the
fruit is ripe.
Seeds colour
in the closed
fruit
370 STUDIES IN SEEDS AND FRUITS
first considering the " How " of seed-coloration before one
can attempt to think of the " Why." One of the first things
that struck me in this connection was the circumstance that
many a pretty hue in seeds comes and goes in the fruit before
its seeds are exposed (by its dehiscence or its breaking down)
to the air. This is well seen in Abrus precatorius and Adenan-
thera pavonina^ where the scarlet coloration of the normal rest-
ing seed is preceded by a pretty rose-pink colour in the soft
unripe seed. The seeds of Ravenala madagascariensis (the
Travellers' Palm), when wrapped in their bright blue arils in
the closed capsular fruit, are very different-looking objects
from the same seeds in the opening fruit, when the aril has
become a dirty brown. Then, again, on cutting open a young
fruit of Barringtonia speciosa, one is a little startled to find seeds,
half an inch in size and not much more than bags of fluid,
coloured deep red, a hue which they lose altogether as the seed
matures in the centre of the fruit. One of the most striking
cases of seed-coloration is seen in the germination of the yellow
seed of Guilandina bonduc^ which, as the hard shell swells with
the absorption of water, assumes a chocolate-brown hue. Such
a seed, when the swelling process has affected one-half of its
surface, is half yellow and half chocolate brown, and presents
thus a conspicuous contrast in coloration.
From the various cases of seed-colouring just noticed, it is
obvious that it would be futile to look for an expknation
before we learn more of the conditions attending and preceding
the coloration of seeds. One of the most important conditions
lies in the circumstance that seeds assume to a greater or less
degree their permanent colours in the closed fruit before they
are exposed to the air either by its dehiscence or decay. This
is not absolutely essential for coloration, but it is as a ruL
essential for normal colouring. I have handled a great man;
immature seeds, and have found that generally such seed:
colour defectively when removed as soft seeds from the greei
fruit. Those seeds that are white when immature and dee]
brown or black when mature often suffer least by beim
SEED-COLORATION 37 1
allowed to colour in the detached state. However this may
be, the point I wish to lay stress upon is that seeds are
coloured in the closed fruits. Though that condition may not
be absolutely essential for the development of colour, it is the
protection which nature supplies to the plant-embryo, and it
is under such circumstances that seeds acquire their hues.
It is to this general condition that attention will be first
directed ; and afterwards inquiry will be made as to whether
the colouring takes place in the green or in the ripe fruit, or in
the drying fruit, or during all stages. Then other matters will
be dealt with, such as the relation between the coloration and
the drying and shrinkage of the seed.
With regard to the general question, it has already been
shown in Chapter XI that in the case of berries, such as those (a) Berries,
of Herberts, Arum maculatum, and Tamus communis, coloration
takes place within the moist fruit, and the same rule applies to
fleshy fruits of the Apple and Sapodilla types and to other
moist fruits. The seeds of Momordica acquire their colours
in the most watery of fruits, the yellowish-brown seed being
enclosed in a bright red soft covering. It is well to notice,
however, that not all fleshy fruits have coloured seeds, to wit,
those of Citrus and Cucumis ; but coloration seems to be more
general in such cases, and when it occurs it takes place inside
the moist fruit.
In the same chapter it was noted that in dehiscent capsules, (6) Capsules,
as illustrated by those of ALsculus Hippocastanum (Horse-
chestnut) and Iris Pseudacorus, the seeds colour before the fruit
opens, the coloration being well advanced in the first case, but
in the second it only reaches the early stage of " browning."
Capsules, as has been shown in Chapter XIII, often dehisce
at an earlier stage than other types of dehiscent fruits, such
as leguminous pods. In such cases it often happens that the
seed-coloration is not complete when the fruit opens, the seeds
deepening in hue after the dehiscence. Under unusual con-
ditions the seeds may not begin to colour until the fruit
dehisces. Thus, the immature soft seeds of the Mahogany,
372 STUDIES IN SEEDS AND FRUITS
according to my observations, retain their white hue until the
capsule opens, when they begin to brown, a circumstance
probably to be connected with the hard ligneous character of
the fruit, the walls of which are 10 millimetres or nearly half
an inch thick.
On the other hand, there is no difficulty in showing that
with capsules and with similar fruits the absence of colouring
before the fruit opens is the exception and not the rule. In
baccate capsules, like those of Thespesia populnea, as already
pointed out in Chapter XI, the white soft seeds of the green
fruit, as they harden, become first purplish and then brown
long before they are freed by the decay of the dried-up fruit.
But here in Devonshire one has not to walk far to find the
same indications in the plants growing around. The seeds of
Iris fcetidissima acquire their orange colour, those of Scilla nutans
become shining black, those of Allium ursinum become deep
reddish brown, and those of Arenaria peploides take on a similar
hue, whilst the capsule is still moist and green and long before
dehiscence occurs. So, again, the seeds of Stellaria Holostea
and of Primula veris redden and brown before the capsule
opens ; whilst the seeds of Aquilegia assume their black hue
in the moist unopened follicle. The common weeds around
one's house in the tropics follow the same rule. In the cases
of Argemone mexicana, Datura Stramonium^ and Portulaca oleracea
the soft white seeds become more or less black in the closed
capsule whilst the fruit is still green and moist. The seeds of
Sesuviutn, a genus of beach plants, behave in precisely the same
way. With Ricinus also the soft white seed hardens and
colours in the green closed coccus.
(c) Pods of In Chapter XI we found the same behaviour in the seeds
plants. of leguminous pods, as exemplified by those of C^salpinia
sepiaria and Ulex europteus. But in legumes the coloration of
the seeds is often more complete when dehiscence occurs than
it is in capsules, because, as established in Chapter XIII, the
fruit opens at a later stage of the drying process. It has
already been indicated that the seeds of capsules often deepen
SEED-COLORATION 373
their hue after the fruit opens ; whilst in leguminous pods the
seed colouring is practically complete when dehiscence takes
place. With Leguminosae this is the general rule whether the
pod regularly dehisces, or breaks up into joints, or liberates
the seeds by its decay. As further illustrations may be
mentioned Abrus precatorius. Acacia Parnesiana, Adenanthera
pavonina, Canavalia gladiata^ and C. obtusifolia^ Dioclea reflexa,
Entada, Erythrina, Guilandina, Leuc<ena, Mucuna, Phaseolus,
Poinciana regia, Vicia^ Vigna luteola, etc.
With regard to the question whether seed-coloration is Does seed
confined to one or all of the three states of the fruit, the green, ^wI^wL
* O * tciKc pia.ce in
the ripe, and the drying, there are so many different determin- ^ reen
,. . r j i ' r , n P e or dry-
ing conditions between one rruit and another that a careful ing fruit?
investigation is requisite before one can venture to reply.
One would infer after watching the seeds of Vida darkening
in the drying and blackening pod, or the Horse-chestnut seeds
as they brown in the drying capsule, that drying is necessary
for their colouring. Here we should undoubtedly be wrong.
On the other hand, we would conclude after observing the
process of seed-colouring in the Blue-bell (Scilla nutans} that
the seeds acquire their shining black hue in the moist green
capsule. Here we should most probably be right. That the
coloration of the seeds does frequently take place in the closed
capsule whilst it is still green and moist has indeed been clearly
shown a page or two back. But the subject is very complicated,
and Nature seems to have done her best to make observation
difficult and immediate inferences hazardous, more especially
with legumes. Here experiment and observation must go
hand in hand.
In the first place, I will take the colouring regime of the Experi-
seeds of Scilla nutans as disclosed by my experiments on the LJbimenko
fruits of the living plant. When I experimented on these
capsules in the summer of 1908, I was not aware that similar interior of
experiments had been made by Lubimenko on the pods of
certain leguminous plants, Pisum sativum, Colutea arborescent, and
Lathyrus latifolius, the results of which have since been published
374 STUDIES IN SEEDS AND FRUITS
in a paper entitled " Etude physiologique sur le developpement
des fruits et des grains" (Comptes rendus^ August 24, 1908).
They are not concerned with the coloration of seeds, but they
are interesting from the light they throw on the conditions in
which it takes place. Selecting very young pods on the living
plant with their sides still in apposition, he removed part of
them by longitudinal sections, and found that they soon
formed a new suture, closed themselves in, and developed
normally. When, however, pods more advanced in growth
and with their inner surfaces no longer in contact were
experimented on, different results were obtained. By cutting
out portions of the sides of the pods so as to bring the young
seeds into direct communication with the outer air, it was
ascertained that the growth of the seeds was arrested, the fruits
falling off in about a week. The conclusions arrived at were
that for the normal development of the seed a confined
atmosphere (une atmosphere confinee] is needed, and that one
of the functions of the pericarp is to maintain the internal
air at a certain stable composition. The green parts of the
pericarp, it is observed, decompose in light the carbonic acid
arising from the respiration of the seeds and prevent its
accumulation inside the fruit. Even in darkness the gas is
kept within certain limits by its slow diffusion from the fruit.
As regards the failure of young pods when the seeds are
exposed to the air through windows cut through the pericarp,
it may be surmised that capsules with their cells or loculi
distinct from each other would be rather more suitable for such
experiments. When an opening is made in the side of an
ordinary legume the whole contents are exposed to the outside
air, whilst in a capsule, by confining the experiment to only one
of the cells, the rest of the fruit would be relatively unaffected.
The author's My own experiments on the green capsules of living
on^he"" plants of Scilla nutans occupied the period between the middle
capsules of Q j une an d the beginning of August, and were limited to one
nutans. cell only in each fruit, the other two being left untouched.
The cell was so incised that the seeds in it were freely exposed
SEED-COLORATION 375
to the air. Though checked by plants in pots kept indoors,
the results as described below were all obtained from plants
growing in a hedgerow and exposed to the ordinary weather-
conditions. In the early stage, when the young seeds are
little more than bags of fluid, they are pearly white. As the
seeds mature and their contents solidify, they become succes-
sively dull white, yellowish, reddish brown, and finally shining
black. The colouring stages and the maturation are completed
in the green moist capsule before dehiscence. When the
fruits were incised in the middle of June the seeds exposed
were soft pearl-like bodies, which, if detached and allowed to
dry, shrank to a mere skin. By the beginning of August the
exposed seeds had reached the brown stage, the last but one
of the stages of the colouring process ; but with the exception
of the difference in hue and their rather smaller size they were
normal hard matured seeds. In the other two closed cells of
each capsule experimented on, the seeds during this period
acquired the typical black colour and were normal in their
other characters. The experiment did not seem to affect the
rate of the changes in the seeds of the other two uncut cells ;
and when the capsules of other plants around were dehiscing,
these two cells were doing the same, displaying normal black
seeds that contrasted in their hue with the brown seeds exposed
in the incised cell. The upshot of these experiments is that
the exposed seeds developed normally, with the exception of
their failure to acquire the final black colour, for which en-
closure in the fruit seems requisite.
The foregoing experiment on the seeds of S cilia nutans will The blacken-
serve to illustrate the complexity of the processes involved
in seed-coloration. 1 will now proceed to discuss more at
length the conditions under which seeds colour in leguminous
pods, and in the first place I will take the blackening and black
mottling of seeds. One of the chief points which we will
endeavour to determine will be the connection between the
coloration of the seed and the drying of the pod. Though
the two processes are so frequently associated, it is quite
Vicia sepium
and Vicia
sativa.
Their
mottled
seeds.
The con-
ditions in
which the
mottling of
Vicia seeds
takes place
376 STUDIES IN SEEDS AND FRUITS
possible that the association is in a sense accidental, and that,
as in the berry and capsule, seed-coloration may occur in the
green moist legume.
The seeds of Vicia sepium and Vicia sativa, which are
usually mottled with black spots on a dark green or greyish-
green ground, will first serve to illustrate this point. After
examining a considerable number of their seeds, one might
think that these plants produced in each case three kinds of
seeds as far as coloration is concerned. There are first the
greyish or greenish-grey seeds, then the seeds with the same
green or grey ground-colours, but mottled with black spots,
and then the seeds that are almost uniformly black, the
mottled seeds being the most frequent and the most typical.
A closer inspection soon makes it clear that the seemingly
uniform black colour really arises from an intensification of the
mottling, and that, in fact, all three kinds have the same ground-
colour, the differences being due to the variation in the extent
of the mottling. In one seed it is almost absent ; in the
typical seed it is well developed ; and in another it is so dense
that the mottled patches largely coalesce.
In both these species of Vicia the soft seed of the green
pod is green, with an embryo of a darker green. When the
blackening and drying of the pod is well advanced these seeds
gradually shrink, harden, and become duller or paler in hue,
and then the black mottling appears, the shrinking of the
cord ushering in the earlier changes. Long before the dehis-
cence of the pod the typical characters of the resting seed have
been formed, and the embryo exchanges the dark green hue
of the unripe soft seed for the dull yellowish colour that is so
characteristic of the resting state of seeds.
With regard to the conditions under which the dark
coloration of the seeds of these two species of Vicia occurs,
the following remarks may be made. On the plant the drying
and blackening of the pod precede the mottling of the seeds,
which belongs to the latter stage of the shrinking and harden-
ing process. But it appears to be essential for the develop-
SEED-COLORATION 377
ment of the black mottling of the seeds that the pods should
be left undisturbed on the plant. No mottling took place in
any of my experiments on detached green pods with soft green
seeds, whether the pod was allowed to dry in air or was placed
in wet conditions, as in water or in wet moss. Experimenting
on the soft green pre-resting seeds, I found that when totally
submerged in water they failed to mottle and that when
allowed to dry in air they did so very imperfectly. But when
a soft green seed was placed on the surface of water so that a
portion was exposed, in the course of a few days the exposed
portion displayed mottling, whilst the under submerged part
remained green. These results seem to signify that mottling
occurs under conditions intermediate between those to which
the air-drying seed and the submerged seed are subjected,
such as would be presented in the confined conditions of the
closed green pod.
These indications of the Vicia seeds will become more
significant when we come to consider those of other
leguminous seeds. It is more difficult than usual in their
case to dissociate the coloration of the seeds from the drying
of the pod ; but the data go to show that the seeds of Vicia are
capable of hardening and of acquiring their dark coloration in
the moist green pod. In this case the drying of the pod
might be regarded as interfering with the completion of the
blackening process ; and in this way the dark mottling would
present itself as the result of a check in the progressive blacken-
ing of the seed. We would thus take it that Vicia seeds are
mottled because they have failed to become uniformly black.
More determinate results are offered in the blackening of
the large, soft, white pre-resting seeds of two other leguminous
plants, Mucuna urens and Dioclea reflexa ; and I will let each
tell its own story.
With Mucuna urens, where the immature seeds in the Theblacken-
green pod are white, the soft unripe seeds harden and blacken sefd of 6
as the pod dries and browns, completing all their changes in Mucuna
the closed pod, though the dark hue usually becomes paler
378
STUDIES IN SEEDS AND FRUITS
The indica-
tions of the
seeds of
Dioclea
reflexa.
Three kinds
of seeds dis-
tinguished
by their
coloration.
and of a blackish grey when the seeds assume the final resting
state. The changes in the seed are preceded by the shrinking
of the fleshy cord or funicle and by the blackening of the
raphe and scar, the rest of the seed's surface remaining for a
time a pure white. These seeds do not mottle ; but it is
significant that though there is every appearance of a connection
between the drying of the pod and the blackening of the seeds,
the soft white seeds when detached blacken much more rapidly
when wetted than when allowed to dry. Here, it seems,
drying retards the process. It may be added that the
subsequent blackening of the shrinking seed is apparently not
connected with the previous blackening of the raphe and scar
when the cord withers. The same thing happens with some
white seeds (like those of Canavalia ensiformis) when the cord
dries up, the black scar remaining a permanent feature of the
white matured seed.
From these indications of the seeds of Mucuna urens we
turn to those supplied by the seeds of the kindred plant,
Dioclea reflexa. These seeds are also white when immature in
the green pod, and when the pod darkens, as it begins to dry
up, the seeds commence to shrink, harden, and blacken. But
there is this difference. The blackening process is usually
incomplete, and mottled seeds result. They also follow the
general rule that the seed acquires its fixed characters as a
resting seed, whether in colour or in other respects, in the
closed pod. As in Vicia saliva and Ficia sepium, three kinds
of seeds as regards their colour can be distinguished, the black
or brownish black, the reddish brown, and the mottled seed
showing black patches on a reddish-brown ground. As in
Ficia also, the mottled seeds are most typical of the plant, and
the mottling may be regarded as the failure of the blackening
process. But in Ficia the black seed represents the end of the
colouring process, whilst in Dioclea it represents the beginning.
When the blackening of a Dioclea seed fails altogether the
seed is reddish brown ; but when the process is only partly
checked there are formed black patches on a reddish-brown
SEED-COLORATION 379
ground. This blackening process accompanies the early
shrinking and hardening of the soft, white pre-resting seed,
and is most active after the seed has lost 20 per cent, of its
weight ; but although often associated with the drying of the
pod, there is good reason for holding that these changes in the
colour, size, and consistence of the seed may occur, as in the
berry, under very moist conditions.
Whilst observing the habits of the plants of Dioclea reflexa The con-
in their home in the forests of the Grand Etang in Grenada, I seed-color-
was able to notice the conditions under which the seed-colora- ascertained '
tion took place. Whilst the reddish-brown and the mottled byobsenra-
tion and ex-
seeds represented those that had undergone the greatest periment.
amount of drying in the pod on the plant, the black seeds
were invariably those obtained from pods lying on the ground
in the most humid parts of the forest, where the seeds failed
to dry properly, and, as remarked in another page, sometimes
dispensed with the resting stage and germinated in the pod.
Such black seeds, when not germinating, possessed coats
insufficiently hardened and still somewhat flexible.
Another indication that the blackening of the seeds of
Dioclea reflexa is most complete under moist conditions was
afforded by the circumstance that when the soft, white unripe
seeds were detached and allowed to dry in a room they always
began to colour and to mottle on the under surface, and were
always much darker below than above. After three or four
days the under surface was usually uniformly black, whilst the
upper surface was only mottled. Such seeds when examined
proved to be sensibly softer and considerably moister on the
lower than on the upper side. Hence it was evident that
a moist surface favoured the blackening process, whilst a
rapidly drying surface retarded it.
Very instructive is the behaviour of the mottled seeds of The mottling
Phaseolus multiflorus (Scarlet-runner). That the source of the fPhaseoius
colouring is in the coats alone and is not connected with the
coloration of the embryo is apparently indicated in the fact runner).
that the embryo is pale green in the unripe or pre-resting
380 STUDIES IN SEEDS AND FRUITS
seeds of both varieties of the plant, the variety with mottled
black and pink or red resting seeds and that with pure white
resting seeds. The seeds of the last named are also white
when very small and undeveloped ; but they need not occupy
further attention here.
The stages in the coloration of the variety with mottled
seeds are as follows. In their immature state, when very small
and soft, the seeds are pale green, with a pinkish or reddish
tinge, the embryo being darker green. As the seeds increase
in size they become uniformly pink or reddish, the embryo
becoming paler in hue. When the seed approaches maturity
as a pre-resting seed the pink colour of the coats deepens,
and dark mottling begins when the soft full-grown seed
commences to harden its coverings. (It may be noticed in
passing that the soft, pink pre-resting seed parts with most of
its colour when placed in water. This helps to explain the
partial blanching which the half-sized pink seeds sometimes
experience in the green pod, a change which has a bearing on
the deprivation of colour in the white seeds of the other
variety.)
The con- During these observations and experiments on the seeds of
which color/ Phaseolus multiflorus some indications pointed to the probability
place ^^ *hat the black mottling and hardening of the coverings were
independent of the drying of the pod, though usually associated
with it. Other signs seemed to show that the mottling only
became at all evident after the pod had begun to dry. How-
ever, the point whether the preliminary drying of the pod was
really necessary, or was merely an accidental association, was
unexpectedly decided by an experiment begun with quite
another object. Some fresh green pods containing only the
large, soft, pink seeds, showing scarcely any black mottling,
were kept in wet moss in a closed tin for nine days with the
purpose of inducing the seeds to germinate without entering
the shrinking stage. However, although no seeds were ger-
minating, all of them, when the tin was opened, had hardened
normally mottled coats. The pods themselves were com-
SEED-COLORATION 3 8 1
mencing to rot, but the general conditions under which the
seeds underwent these changes must have been those of
extreme moistness. Without intending it, I had induced
these seeds to colour, harden, and probably shrink a little as
well, under conditions as moist as that of a berry. The
bearing of the results of this experiment has been dealt
with elsewhere. Here we will merely accept their indi-
cation that the black mottling and induration of the coats
of the seeds of Phaseolus multiflorus have but little to do
with the drying of the pod with which they are so generally
associated.
The results for the seeds of the four leguminous genera The black
*
of plants above discussed are below tabulated. Though it is
not easy at first sight to pick up the thread of the tangled data,
one inference seems to shape itself out of all the observations bythedrying
and experiments, namely, that the black mottling and dark
coloration of the seeds is not determined by the drying of the
pod. From its close association with these processes in the
seed-coverings, the drying of the pod has certainly all the
appearance of having much to do with them. But we have
seen that in berries, as well as in many capsules, seed-coloration
can have little to do with the drying of the fruit.
This inference, though here drawn with regard to the black but may
coloration of leguminous seeds, applies also to the brown conditions as
coloration of seeds of this and other families, as will be brought S^e of the
out below, and probably to seed-coloration in general. In the berry.
berry and closed capsule, the soft pre-resting seed colours,
hardens, and shrinks under conditions exceptionally moist.
But the same capacity of colouring and hardening their coats
under moist conditions is exhibited by the seeds of legumes,
though in nature disguised by its association with the drying
of the pod. We cannot also doubt that the early shrinking
which accompanies the coloration and the hardening of
leguminous seeds is at the same time an independent process,
and is similarly not connected with the drying up of the
fruit-case.
382 STUDIES IN SEEDS AND FRUITS
TABLE ILLUSTRATING THE STAGES IN THE BLACKENING AND BLACK
MOTTLING OF LEGUMINOUS SEEDS.
Colour of the Coats.
Colour of embryo.
Pre-resting seed
Resting seed of
of green pod.
dry pod.
Pre-rest-
Resting
ing seed
seed
Full-
grown.
Whilst
shrinking
detached
from pod.
Whilst
shrinking
normally
in pod.
Prema-
turely
shrunken.
Normally
shrunken.
of green
pod.
of dry
pod.
Mucuna urens
White
Blacken-
Blacken-
Blackish
Dark grey
White
ing
ing
Dioclea reflexa
White
Blacken-
Mottling
Blackish
Black
...
White
ing
mottling
on reddish
brown
ground
(
Green
Dull green
Mottling
Dull green
Black
Green
Yellow-
Vicia sativa
or grey ;
or grey ;
mottling
ish
Vicia sepium |
no mot-
no mot-
on a grey
.1
tling
tling
ground
Phase olus multi-
florus
(a) mottled
Pink or
Not mot-
Deeper
Not
Black
Pale
White
black seeds
reddish
tling
pink ;
mottled
mottling
yellow-
begins to
on pink
ish
mottle
or red
green
ground
(b) white seeds
White
White
White
White
Pale
White
yellow-
ish
green
The brown
colour of
seeds
On account of its predominance as the colour of seeds,
brown deserves especial attention. As in the case of black, the
indications by no means lend themselves to an easy interpre-
tation. The brown coloration of resting seeds, which may
vary in shade from a pale hue, as in Mahogany seeds, to a
blackish brown, as in old seeds of Entada scandens, seems to be
usually developed in seeds that were white in the soft, moist,
unripe condition. That the browning process, whether in the
leguminous pod or in the capsule or in the berry, is usually com-
pleted before the seeds are exposed to the air has been already
established in this and in previous chapters. In all cases it is
SEED-COLORATION 3 8 3
associated with a shrinking and hardening of the soft, unripe, and
pre-resting seed. But the brown coloration, with its associated
processes, is to be noticed alike under moist conditions, as in
baccate fruits, or under dry conditions, as in drying capsules and
leguminous pods, a subject dealt with in preceding chapters.
Although seeds acquire their brown colour in the closed not con-
capsule and pod, their coloration, early shrinking, and harden- ^ e drying of
ing are so conspicuously associated with the early drying of the fruit
the fruit that it is not a matter for surprise that there should
seem to be some causal connection between them. However,
experiment showed that these changes in the seed may take
place where no drying of the fruit has occurred. Perhaps the
most conclusive piece of evidence in this direction is afforded
by the aborted seeds of the Horse-chestnut (Msculus Hippocas- Horse-
tanum). In full-grown moist capsules showing no signs either
of dehiscence or of drying, and containing full-sized white
moist seeds, it is not uncommon to find two or three aborted
seeds only 2 to 4 millimetres across, but typically brown
and hard-coated. The behaviour of the white moist seeds in
a full-grown green capsule that has been placed in wet moss in
a closed tin is also very significant. Though the capsule at the
end of the experiment shows no signs of drying, since the air
in the tin would be quite saturated with moisture, the seeds in
a few days become normally brown, and experience a slight
shrinking in size and a hardening of the coats. In spite,
therefore, of their moist conditions, the Horse-chestnut seeds
in this experiment experience the same changes that they
exhibit in the drying capsule, thus behaving like the seeds of
a berry.
We can therefore no longer suppose that the drying of The regime
the capsule is needed for the preliminary shrinking, hardening, ^reproduced
and coloration of the seeds within. In the case of brown or H 1 the c lou /-
mg seeds of
black seed-coloration the inference is the same. In the pod, the pod and
as shown in the case of Phaseolus multiflorus, and in the capsule,
as illustrated by sEsculus Hipp ocas tan urn, the regime involved
in the coloration, early shrinking, and preliminary hardening
The brown-
ing of unripe
seeds in
capsules and
pods is
associated
with shrink-
ing and
hardening
of the coats.
384 STUDIES IN SEEDS AND FRUITS
of the seed and its coats is that which is displayed by the
colouring, shrinking, and hardening seed in the moist berry.
Whatever the nature of the connection may be, there is
no doubt that the browning process of soft unripe seeds is
associated in capsules and in leguminous pods with shrinking
and hardening of the seed-coats. It has already been shown in
the case of the soft, moist white seeds of the Horse-chestnut
(ALsculm Hippocastanum) that they suffer a loss of 1 7 per cent.
of their weight during the browning that accompanies the
preliminary drying in the closed capsule (see Chapter XI). In
the instance of Entada scandens, where the soft white seeds on
removal from the green pod were allowed to dry on a table,
the seeds did not attain their normal dark reddish-brown hue
until they had lost about half of their weight. Passing through
a preliminary yellowish stage, they lost in five or six days about
20 per cent, of their weight and became a light mahogany brown.
After between two and three weeks, when they had lost about
55 per cent., they assumed the typical colour of the resting seed,
the drying process being prolonged until the loss amounted to
60 per cent. The white soft seeds of Entada polystachya turn
brown in a similar way ; and here the two varieties, the large
pale brown seed containing 10 per cent, of water, and the small
dark brown seed with only 6 per cent., clearly show that the
colour deepens as the seed becomes drier (see Chapter V). The
white flabby seeds of the closed woody capsule of the Mahogany
tree (Swietenia Mahoganf] harden and turn light brown in four
or five days after their removal. As a final example, the seeds
of Iris Pseudacorus may be taken, which, when first exposed by
the opening capsule in the early stage of browning, have already
lost about 20 per cent, of their original weight as soft white
seeds. It should, however, be observed that with fruits ripen-
ing late in the season, as, for instance, in October instead of
the latter part of August and in September, the seeds may
be drier and farther advanced in the browning process before
dehiscence occurs. Such fruits, however, are backward in
maturing, and may even fail to dehisce altogether.
SEED-COLORATION
385
A curious distinction between capsules and legumes unfolded
itself as I collated my notes on fruits and seeds. As shown in
the subjoined comparison of the results given in the following
tables, the so-called immature or pre-resting seeds of capsules
are usually white, whilst those of leguminous pods are usually
green. The proportion of green seeds would have been still
greater for the pods, if herbaceous leguminous plants had
been as well represented as a strictly natural comparison would
have required. The green immature seed is typical of the
dehiscent legume, as is shown in the general table. Nearly all
the pods with green seeds are thus characterised. On the
other hand, the pods with white unripe seeds are generally
indehiscent, as in Mucuna, or break up into closed joints, as
in Entada.
SUMMARY OF THE TABLES GIVEN BELOW, SHOWING THE COLOURS OF
UNRIPE OR PRE-RESTING SEEDS IN DIFFERENT KINDS OF FRUITS.
Indication
that unripe
seeds are
usually white
in capsules
and green in
leguminous
pods.
Number of genera experimented on.
Total.
With green
seeds.
With white
seeds.
With seeds of
other colours.
Legumes
Capsules
Berries . .
35
3 1
7
24
5
3
S
26
4
3
With the exception of Canavalia the genera behave uniformly.
As frequently happens in such cases, a number of points
have arisen during the development of this distinction, which it
is now too late for me to elucidate. Though in the habit of
noting the colour of immature seeds, I did not discover its
significance as a distinction between types of fruits until I
came to elaborate my notes on seed-coloration. 1 will not
enlarge on this distinction here ; but some of the characters
associated with it will be noticed when I deal a page or two
later with white and green immature seeds and with the colour
of the embryo. Below are appended the tables to which the
summary of results above given refers.
25
3 86
STUDIES IN SEEDS AND FRUITS
THE COLOURS OF IMMATURE AND MATURE SEEDS IN LEGUMES,
CAPSULES, AND BERRIES.
I. LEGUMES.
Colours of seeds.
Special characters
of legume.
Immature
(pre-resting).
Mature
(resting).
Abrus precatorius .
Pink
Scarlet
Acacia (near arabica)
Pale green
Dark brown
,, Farnesiana
White, then pale
n
Indehiscent,
green
pulpy
Adenanthera pavonina .
Green, then
Scarlet
yellow, then
pink
Bauhinia (species of)
Green
Black
Cassalpinia Sappan
>
Light brown
I
,, sepiana . j-
(A) Green
(B) White
Mottled black
and brown
...
Cajanus indicus
Green
Pale brown with
slight black
mottling
Canavalia ensiformis
White
White
,, gladiata
Pink
Dull red
, , obtusifolia
White
Mottled brown
Cassia bicapsularis
Green
Dark brown
,, fistula
M
Light brown
Cytisus Laburnum
Deep brown
Dioclea reflexa
White
Mottled black
Indehiscent
and brown
Entada polystachya
,, scandens .
M
Brown
Reddish or
blackish brown
} Breaks up into
closed joints
Faba vulgaris (Broad Bean) .
Yellowish white
Brownish green
Genista (species of)
Green
Chocolate brown
Guilandina bonducella .
Yellowish green,
Lead grey
...
then olive
Lathyrus pratensis
Green
Mottled black on
light ground
Leucsena glauca .
j }
Dark brown
Lotus corniculatus
99
Mottled bl a c k
...
and brown
Mucuna urens
White
Blackish
Usually inde-
hiscent
Phaseolus multiflorus (A)
Pink
Mottled black on
pink or red
ground
(B) .
White
White
Pisum sativum (wrinkled)
Green
Green
,, (unwrinkled) .
jj
Yellowish white
Poinciana regia
Pale green
Mottled black on
Tardily d e h i s-
light grey
cent
ground
Sophora tomentosa .
Spartium (species of)
Yellowish green
Green
Pale brown
Dark brown
SEED-COLORATION
I. LEGUMES continued.
387
Colours of seeds.
Special characters
of legume.
Immature
(pre-resting).
Mature
(resting).
Ulex europseus
Vicia Cracca . . .
Green, then
yellow
Green
Chocolate brown
Dark mottled
ii
Dark brown
,, sepium.
Vigna luteola
ii
II. CAPSULAR FRUITS.
Colours of seeds.
Special characters
Immature
Mature
Ul Hull.
(pre-resting).
(resting).
^Esculus Hippocastanum
White
Dark brown
(Horse-chestnut)
Allium ursinum
91
Blackish
Aquilegia (species of) .
Green
Black
Follicular
Arenaria peploides
White
Dark brown
...
Argemone mexicana
)>
Black
Bignonia (species of)
'>
Light brown
Siliquiform
Carma indica
5J
Black
Cardiospermum grandiflorum
Green
>i
Convolvulus Batatas
White
>
Datura Stramonium
j
Digitalis purpurea
Pale green
Reddish brown
Dodonaea viscosa .
Black
Gossypium barbadense .
White
M
Hypericum Androsaemum
...
Ipomoea pes-caprse
Brown
...
,, tuba
ii
,, tuberosa .
Black
Iris fcetidissima
Scarlet
,, Pseudacorus
Light brown
...
Lychnis diurna
Blackish
,, vespertina
Brown
Papaver Rhoeas
Blackish
...
Portulaca oleracea
Black
Primula veris
Green
Brown
...
Ricinus communis
White
Mottled black
Tri-coccous
on grey ground.
Scilla nutans
Black
Sesuvium portulacastrum .
,,
...
Stellaria Holostea
Red
.
Swietenia Mahogani
Light brown
Ligneous
Thespesia populnea
Brown
Baccate
Veronica ....
ii
3 88 STUDIES IN SEEDS AND FRUITS
III. BACCATE FRUITS.
Colours of seeds.
Special characters
of fruit.
Immature
Mature
(pre-resting).
(resting).
Arum maculatum .
White
Reddish
Berberis (species of)
Green
Brown
Chrysophyllum Cainito (Star
White
,,
Apple)
Momordica Charantia
11
Yellowish brown
Baccate capsule
Passiflora pectinata
Green
Purplish
Pyrus Malus (Apple)
Tamus communis .
White
Greenish yellow
Brown
M
The green
hue of the
unripe seed
has but little
influence on
the colour of
the resting
seed with
leguminous
plants.
As seen in the previous table, green pre-resting seeds
are frequent with Leguminosae. A few of the plants there
named are albuminous, having large foliaceous embryos of
almost the length and breadth of the seed, and enclosed
between two slabs of albumen, namely, Bauhinia, Cassia
fistula, and Poinciana regia. Speaking of leguminous seeds
in general, there seems usually to be little or no connection
between the green coloration of the unripe or pre-resting
seed and the ultimate hue of the resting seed. Thus with
the seeds of Adenanthera pavonina, the successive stages of
coloration in the pod are green, yellow, pink, and, finally,
scarlet. It seems rarely to happen that the green hue of
the unripe seed is retained in the resting seed. This,
however, occurs with the wrinkled varieties of Peas, Pisum
sativum. In smooth Peas the green is replaced by yellowish
white. Then, again, the green colour of the immature seed
may be exchanged in the resting seed for black, as in
Bauhinia ; for different shades of grey, as in Guilandina
bonducella ; for light brown, as in Cassia fistula ; for dark
brown, as in Leuc<ena glauca ; for chocolate brown, as in
Ulex europ<eus ; and for a black mottling on a light ground,
as in Vicia, Poinciana regia, C<esalpinia sepiaria, and Cajanus
indicus.
SEED-COLORATION 389
Nor can we look for an explanation of this variation in The colour
colour of the resting seed to the colour of the embryo in the bryo in the
pre-resting or unripe seed. Thus exalbuminous seeds like and*restine
those of Pisum sativum (unwrinkled variety), C<esalpinia Sappan* seeds has no
TTJ rr ^ T ? 1-1 j- i influence on
Ulex europteus, Viaa sativa, Lyttsus Laburnum, etc., which display the final
great differences in coloration in the resting seed, all have
green embryos as well as green coverings in the soft unripe seed -
condition ; and the same remark applies to the albuminous
seeds of Bauhinia, Cassia fistula, and Poinciana regia.
If we expect to find a clue in the colour of the leguminous
embryo in the resting state, we shall be also disappointed.
There is a uniformity of colouring in the embryo of the
resting exalbuminous seed which stands in no sort of relation
with the varied colouring of the coats of such seeds. As the
green embryo enters the resting state, its assumption of a pale
yellow or brownish-yellow hue indicates the destruction of the
chlorophyll. That green embryos thus change their colour
when the immature soft seed contracts and hardens in the
shrinking stage seems to be a general rule. This is brought
out by the table below in my discussion of green embryos of
leguminous seeds ; but more examples might be given, where,
although I have no note of the colour of the embryo in the
immature seed, its green colour is indicated by its yellowish
coloration in the resting seed, as, for instance, in Albizzia
Lebbek.
In making further reference to the green embryos so In unripe
i / j . . i leguminous
commonly round in unripe or pre-resting leguminous seeds, seeds green
one must notice that when the embryo is green the seed-coat is Qt f^^^
generally green, but of a markedly paler shade. However, it usually go
is not difficult to find exceptions to the rule amongst exal-
buminous seeds. Thus with Entada polystachya the coats of
the soft unripe seed are white, but the enclosed embryo is
bright green ; whilst with the Broad Bean (Faba vulgaris] the
embryo is bright green and the coats are white, tinged faintly
with greenish yellow. Nevertheless, as indicated in the
samples given in the table below, it is evidently the rule for
390
STUDIES IN SEEDS AND FRUITS
TABLE SHOWING THE COLOURS OF THE SEED-COATS AND OF THE
EMBRYO IN SOFT IMMATURE, AND HARD MATURED OR RESTING
LEGUMINOUS SEEDS.
AlKn
A1DU-
minous
Seed-coats.
Embryo.
or
exalbu-
minous
indicated
by
A. and E.
Immature
(pre-
resting).
Matured
(resting).
Immature
(pre-
resting).
Matured
(resting).
Acacia Farnesiana .
E.
Green
Brown
Green
Pale yellow
Bauhinia (species) .
A.
Black
ii
ii
Csesalpinia Sappan .
E.
Light brown
Yellowish
i)
green
Cassia bicapsularis .
A.
Dark brown
Green
i
,, fistula . .
A.
Light brown
i 1
Cytisus Laburnum .
E.
Dark brown
Entada polystachya
E.
White
Brown
ii
Faba vulgaris
E.
Yellowish
Brownish
ii
(Broad Bean)
white
green
Genista (species) .
E.
Green
Dark brown
ii
Guilandina bondu-
E.
u
Grey
White
cella
Lathy rus pratensis .
E.
>)
Mottled black
Green
ii
on light
brown ground
Leucsena glauca .
E.
i
Dark brown
u
ii
Phaseolus m u 1 1 i-
E.
Pink
Mottled black
Pale green
White
florus
on pink
ground
Phaseolus m u 1 1 i-
E.
White
White
ii
ii
florus
Pisum s a t i v u m
E.
Green
Green
Green
Green
(wrinkled)
Pisum s a t i T u m
E.
M
Yellowish
Pale yellow
(unwrinkled)
white
Poinciana regia
A.
f>
Dark mottled
>i
M
Sophora tomentosa
E.
Yellowish
Light brown
Pale green
ii
green
Spartium (species) .
E.
Green
Dark brown
Green
ii
Ulex europseus
E.
,,
Chocolate
u
11
brown
Vicia Cracca .
E.
Dark mottled
it
M
,, sativa .
E.
it
ii
II
sepium . .
E.
n
ii
1)
SUPPLEMENTARY RESULTS FOR SEEDS OF OTHER ORDERS.
Thespesia populnea
A.
White
Brown
Whitish
Whitish
Gossypium barba-
A.
u
Black
Pale greenish
Dirty white
dense
yellow
Dodonsea viscosa
E.
Pale green
,,
Pale green
Pale yellow
Convolvulus Batatas
A.
White
Dark green
ii
Ipomcea tuba .
A.
u
Brown
ii
ii
SEED-COLORATION 391
this family, both for albuminous and exalbuminous seeds,
that in the pre-resting or so-called immature state green
embryos and green seed-coats go together.
In this connection I come now to refer especially to the The colour-
behaviour of the embryos of albuminous seeds. The changes the embryos
in colour which the green embryos of full-sized unripe seeds QUS see^ n "
undergo when entering the resting stage, and subsequently
when germination begins, are well illustrated for leguminous
plants by Poinciana regia, Cassia fistula, and Bauhinia. These
seeds are similar in the general sense that the embryos, which
have large foliaceous cotyledons, are nearly as long and as broad
as the seed, and are placed between two slab-like masses of
albumen. When these seeds are here characterised as unripe
or immature, reference is made only to those seeds that have
reached the maximum size in the soft condition in the green
pod. In such seeds the embryos, being fully formed, are, as
shown in Chapter XIX, quite able to dispense with the rest-
ing stage altogether, and to proceed with their growth, or to
germinate, as we term it. But on account of the cutting
off of the fluid supplies and the drying of the pod, a resting
period is imposed upon them. It is this break in the continuity
of its life that is strikingly shown in the changes of the colora-
tion of the embryo.
In this respect my remarks will be mainly confined to the as illus-
behaviour of the embryo of Poinciana regia, and I will make seeds of
but a brief reference to those of the other two plants, since Pom
regia.
they behave in a similar manner. In a green semi-ligneous
pod of full size the seeds of Poinciana regia are pale green,
and possess soft, flexible coverings. The albumen is white
or colourless, and remains so during the subsequent stages.
The embryo has dark green cotyledons and a white caulicle
or stem ; whilst the pale green plumular bud, which is partly
expanded and stands 3 millimetres high, is far more suggestive
of a continuously growing plantlet than of an embryo that
is shortly to be compelled by the stress of circumstances to
enter the rest-period. When the pod begins to dry and to
392 STUDIES IN SEEDS AND FRUITS
turn brown, the seeds respond ; and as they shrink become
much paler, almost white, except in the centre, which becomes
darker. The embryo is also paler. When the pod has
become dry and the seeds have acquired their normal resting
characters, the signs of active life are gone. The entire
embryo has now a yellowish hue, and the plumular bud,
that was beginning to expand before the influences resulting
in the suspension of the life of the embryo prevailed, has
now closed up again, its tiny leaves being closely appressed.
But the impress of the rest-period remains after the seed has
begun to germinate. The signs of wakening vitality in the
embryo in the early stage of germination are only displayed
in the lengthening of the axis or stem by the growth of the
radicle. The cotyledons maintain their yellowish, lifeless hue ;
whilst the plumule bleaches and becomes quite colourless,
making little or no effort to unfold its leaves again, until
the protruding radicle exceeds three-fifths of an inch in length.
The bleaching of the green plumule of the pre-resting seed
as the resting stage is reached probably occurs also with
cucurbitaceous plants. It seems to happen with the Walnut
(Juglans). Lord Avebury speaks of the plumule bearing five
or six rudimentary leaves " often just tipped with green "
(Contribution to our Knowledge of Seedlings, i. 8).
The lethargy displayed in the waking up of the dormant
embryo of Poindana regia came quite as a revelation to me.
For some time after the radicle has struck into the soil the
plantlet's existence is mainly hypocotylar and scarcely cotyle-
donary or plumular. The plumular bud is very slow to
unfold its tiny leaves, so long closed up during the rest-
period ; but gradually it assumes a pale greenish -yellow
colour. So also the cotyledons retain their yellowish, lifeless
hue during all the germinating process* But notwithstanding,
they considerably increase in size by absorbing the albumen ;
and by the time they have extricated themselves from the
seed-case there is but little of the reserve food left. They
soon then acquire a more active green, and the plumule
SEED-COLORATION 393
similarly responding to the young plant's needs, vigorous
growth begins.
The lesson of the embryo of Poinciana regia will be dealt
with in Chapter XIX, where the general subject of the rest-
period of seeds is discussed. Brief reference will now be
made to the other two leguminous plants possessing the
same seed-structure, namely, Cassia fistula and Bauhinia. They Cassia
..,*,. . r i fistula and
behave in a similar rashion as regards the coloration or the Bauhinia.
embryo, which in the immature seed is bright green in the
first-named and pale green in the last-named plant ; but in
both cases it assumes a pale yellowish hue when the seed
enters upon the resting stage.
The alteration in the colour of the embryo in seeds of Npn-legu-
the foregoing type, where the embryo with large foliaceous seeds, such
cotyledons lies between two slabs of albumen, sometimes
amounts to complete decoloration as the seed proceeds with Cofubrina
. asiatica.
its development. Thus, in Hura crepitans (Euphorbiaceae) the
embryo is coloured green only in the earlier stage of the
growth of the seed. When the seed has attained its full size
in the ripening fruit, and before the drying process has begun,
the embryo is already white, and that state it retains. It
would seem that the embryo in seeds of this type, whether
it be white or yellowish in the resting seed, has usually
functioning green cotyledons in the unripe or pre- resting
seed. This seems to be true also of the seeds of Ricinus
community in which, although (as I found) the embryo of the
resting seed is always colourless, the cotyledons may be green
in the pre-resting stage (see PfefFer's Physiology of Plants^ i. 596).
It may be inferred again in the case of Colubrina asiatica
(Rhamnaceae), where resting seeds of the same structural type
have pale yellow embryos.
Since in the leguminous embryo the hypocotyl is relatively The colour
insignificant, the cotyledons making up its mass, I have usually
spoken of green embryos rather than of embryos with green
cotyledons. It would seem, however, that in this family when green.
the cotyledons are green the caulicle or hypocotyl may be
394
STUDIES IN SEEDS AND FRUITS
The fre-
either white or green. But this point has only arisen during
the preparation of these pages ; and I append a few results
of observations respecting it in the case of plants ready at
my hand.
OBSERVATIONS ON THE COLOUR OF THE HYPOCOTYL OR CAULICLE
IN EMBRYOS OF SOFT, FULL-GROWN, UNRIPE SEEDS WHEN THE
COTYLEDONS ARE GREEN.
(With the exception of the two last in the first column all are leguminous.)
Entire embryo green.
Cotyledons green,
hypocotyl white.
Cytisus Laburnum.
Vicia sepium.
Acacia (species).
, , sativa.
Lathyrus pratensis.
, , Cracca.
Leucsena glauca.
Poinciana regia.
Genista (species of).
Faba vulgaris.
Cassia bicapsularis.
Ulex europseus.
Pisum sativum.
Sophora tomentosa.
Spartium (species of).
Euonymus.
Acer Pseudo-platanus.
Note. When the entire embryo is green, and the colour is dark, the hypocotyl is
often paler than the cotyledons.
With the exception of wrinkled Peas (Pisum sativum\ green
embryos have not often come under my notice in the typical
restm g seed. That they are not infrequent, however, is
shown in the statement made in The Natural History of Plants
(i. 622) of Kerner and Oliver that in Firs and Pines, Maples,
and some Crucifera, in Loranthus, Mistletoe, and the Japanese
Sophora^ the cotyledons are green whilst enclosed in the seed y
their epidermis being provided with stomata. In this connection
it may be noted that fruits of the Sycamore Maple (Acer Pseudo-
platanus\ which I have been keeping for nearly two years, have
embryos dark green in hue. It should be remarked that in
the green fruit of this tree the green embryo is enclosed in
whitish seed-coverings. Here also reference may be made
to the dark green embryo of the seed of Montrichardia
arborescenSj an arborescent aroid that came under my observation
SEED-COLORATION 395
in Tobago and Grenada. The seed is exalbuminous, and has a
thin covering or skin, which, if I remember rightly, is brownish
in colour. As I write I have by my side the exalbuminous
seeds of Monstera pertusa, a climbing aroid, gathered in Grenada
over a year ago. In this case also the embryo is dark green.
Further details on this subject will be found in Note 18 of
the Appendix.
Before leaving the subject of the colour of embryos, a Theconnec-
few more remarks may be made on the relation in ex- albuminous
albuminous seeds of the Leguminosae between white embryos
and the colour of the seed. If we can judge from the between
behaviour of the genera Canavalia and Phaseolus, where bryosand
white embryos seem characteristic, there is no connection ^
between the two. The four species of Canava/ia with which
I am acquainted, C. ensiformis^ C. gladiata^ C. obtusifolia, and
a Tobago species, of which the specific name is unknown to
me, all have white embryos. In the first the seed is white,
in the second dull red, in the third banded brown, and in the
last pale brown. The same indication is afforded by four
kinds of Phaseolus, all of which have white kernels or embryos,
namely, P. vulgaris (French Bean), with reddish-brown seeds ;
P. multiflorus (Scarlet-runner), having two varieties, one with
seeds showing black mottling on a reddish ground, the other
with white seeds ; and a West Indian species with white seeds.
From these data it would seem that, as already pointed out in
the case of leguminous exalbuminous seeds where the embryo
is green in the unripe and yellowish in the resting seed, there
is no connection between the colour of the embryo and the
coloration of the seed-coats.
The hard red seeds of different species of tropical The red
leguminous plants, such as Abrus precatorius, Adenanthera f^umin
pavonina, different species of Erythrina, etc., invite attention for P lants -
many reasons. As presented to view in the opening pods,
they must often attract the notice of birds ; but with the
exception of Erythrina and Adenanthera 1 have not come upon
many references to birds selecting them for food. In my
39 6 STUDIES IN SEEDS AND FRUITS
book on the Solomon Islands (p. 293) allusion is made to my
finding cracked seeds of Adenanthera pavonina in the gizzard
of a Nicobar pigeon, and it is evident that they also serve as
food for Indian parrots (Mr J. Scott in More Letters of Charles
Darwin, ii. 349). Then, again, the Layards observed in New
Caledonia that a small crow and different species of parrots
fed on the seeds of Erythrina (Ibis, vi. 1882). But this is all
that I know of the matter. Mr P. H. Gosse in his book on
The Birds of Jamaica names a number of seeds that are eaten
by them, but no mention is made of any of the hard red seeds
above noticed.
The con- I will here confine my attention to the conditions under
whidfthe which such seeds acquire their red colour and to the changes
red colour is they experience in this respect when absorbing water for
the changes germination, as illustrated by those of Abrus precatorius, Aden-
dui-ing anthera pavonina, and Canavalia gladiata. All three have these
germination. f ea t ures i n common. They go through the shrinking and
colouring processes in the closed pod ; in all of them the soft
unripe seed is rose-pink in hue, the change from pink to red
representing the last stage in the coloration ; and, lastly, the
colouring matter is readily dissolved out in water, when the
coats are pierced or the cuticle is not intact.
Canavalia In the case of Canavalia gladiata the soft, unripe, rose-pink
seed belongs to the green pod. As the pod dries, the shrink-
ing and hardening seed assumes a bright red hue, and by the
time the pod is well dried and on the point of dehiscence the
seed is fully contracted and dull red. Whilst drying, the pod
does not discolour or darken, as seems to be the rule with
legumes having dark-coloured seeds ; but it becomes gradually
paler, and finally has a light brown, parchment-like appearance.
When absorbing water and swelling for germination, the seed
first resumes its original pink hue and then becomes a chestnut-
brown. As shown below under Abrus precatorius, where the
same thing occurs, this return of the germinating seed to the
colour of immaturity is really due to the hydration of the
coverings, the colouring matter being to some extent washed
SEED-COLORATION 397
out, so that the coats have the sodden, wrinkled appearance of
a washerwoman's fingers.
With Abrus precatorius, as with Canavalia gladiata^ the Abrus pre-
characters of the resting seed are all acquired in the closed
pod. Here again the pink colour of the soft immature seed
in the green pod gives place to a scarlet red in the hard
matured seed of a pod about to open ; and here also, when
the seed swells for germination, it resumes the original pink
hue of immaturity. With both these plants there is but little
difference either in colour, size, or consistence between an
immature seed taken from a green pod and a resting seed that
has swollen for germination. That this change from red to
pink in the germinating seed is due to the hydration of the
coverings is indicated by the behaviour of the seed when
allowed to soak in water after being filed. The colouring
matter dissolves out and the red seed becomes almost blanched.
In the case also of the seeds of Adenanthera pavonina all Adenanthera
the colour-changes take place in the closed pod. As observed pai
for me by Mrs H. B. Warde in Jamaica, the soft immature
seeds in the green pod are first green and then yellow ; and as
the pod begins to brown and dry the seeds turn pink, and
when the shrinking and hardening processes approach comple-
tion the permanent bright red hue is assumed. It is not
necessary for the development of the last two stages in the
coloration that the pod should remain connected with the
plant. If the green pods are allowed to dry after picking,
bright red seeds will be found in closed pods after a few weeks.
Though I had not the opportunity of observing the actual
stages in coloration on the tree, specimens of all of them were
kept for me. When the seeds are absorbing water and swell-
ing for germination, they do not, as with those of Abrus
precatorius and Canavalia gladiata^ regain the pink hue of
immaturity. The outer red skin is thrown off by the swelling
of the under layer, and the seed assumes the yellowish colour
of the second stage of coloration in the green pod, a stage
earlier in immaturity.
39 8 STUDIES IN SEEDS AND FRUITS
Theyong The red seeds of these three plants are more or less
impermeable to liquid water. With Adenanthera pavonina all
colour de- t h e seec j s are typically impermeable, with Abrus precatorius the
pends on the . i i ,0 7-77-
impermea- great majority are, and with Lanavalia giadiata the minority
seed perhaps are impermeable. The impermeable seeds are of
necessity non-hygroscopic, whilst the permeable seeds behave
hygroscopically. A seed that responded in its changes of
weight to the varying degrees of humidity of the atmo-
sphere could scarcely be expected to retain its bright red
hue for a long period. Where the impermeable cuticle
remains intact the colour ought to withstand the test of
centuries. This would probably be true of the seeds of
Adenanthera pavonina. Except when kept in unusually
dry conditions, I should not expect the seeds of Abrus
precatorius to preserve untarnished for many years their
original scarlet hue, since the scar is their point of weak-
ness. As an indication in this direction I may refer to 35
seeds of Abrus precatorius^ now beside me, which I gathered
from the plant in Fiji twelve years ago. Only 25, or
71 per cent., retain their original bright colour, the rest
being brownish or even blackish in hue. This is a point
in the history of red seeds that seems to be worthy of
further investigation I mean the permanence of the colour.
Abundant data would be at hand in our own museums and in
tropical countries.
Red seeds do I may here refer to a curious fact that must be well known
to students of vegetable chemistry. Although the red seeds
of Abrus precatorius^ Adenanthera pavonina, and Canava/ia
giadiata stain water freely when the water is allowed to
penetrate their coats, the solution has not the colour of the
seeds. The seeds of Adenanthera impart a beautiful amber hue
to the water, which deepens after the seeds have been removed
and becomes like brown sherry. On the other hand, the
seeds of Abrus and Canavalia stain the water a dark green,
which deepens after the seeds have been taken out, becoming
steely or almost inky.
SEED-COLORATION 399
The colour of the kernel or embryo in the case of these The colour
three red seeds in the resting state varies somewhat. In kernels in
Adenanthera pavonina it is yellowish, which indicates that the ^ d seeds of
embryo was green in the unripe seed. In Canavalia gladiata osae.
it is white. In Abrus precatorius it is tinged yellow outside,
but is white on section.
Before quitting the subject of red seeds I will briefly refer The stages
to the stages of coloration of the orange or scarlet seeds of tion^niie" 1 "
Iris fcetidissima^ as observed by me during two seasons in a seeds of iris
wood at Salcombe. All the stages took place in the moist
closed capsule long before the fruit dehisced or showed any
signs of drying up. Up to the middle of August, when the
fruits were dark green and averaged from 100 to no grains in
weight, the seeds were white and soft, with jelly-like contents
and no recognisable embryo. After this, as the capsules con-
tinued to increase in size the seeds became pale yellow ; but
their contents remained unchanged until the end of the month,
when they began to solidify. September was principally
occupied with the maturation of the seeds and with the growth
of the fruit, the seeds assuming a deeper yellow hue. By the
middle of October, when the capsules averaged 160 to 170
grains in weight, the seeds were solid, of full size, and of the
typical orange or scarlet colour. There was not much altera-
tion either in seed or fruit after this date, and in the beginning
of November the most advanced capsules commenced to
dehisce, and the remainder followed during the course of the
month.
It is worth noting that seeds may acquire much of the Thecolora-
coloration which they possess as resting seeds whilst their JS^st their 8
contents are still fluid and before the embryo is formed, contents are
This would seem to take place chiefly with monocotyledonous
albuminous seeds of the type below exemplified. Thus, the
white soft seeds of Allium ursinum, when they begin to ripen
in the closed capsule, become dark red, though little more than
bags of water. In the same way, the white soft seeds of the
green capsules of Iris fcetidissima colour yellow as the fruit
400 STUDIES IN SEEDS AND FRUITS
ripens, though the embryo is not yet recognisable and the
albumen is a mere mass of jelly. I should imagine also with
Scilla nutans that seed-coloration precedes the formation of the
embryo, the pearl-white immature seeds being merely sacs of
fluid. Reference has already been made in the early part of
this chapter to the red hue of the seed of Barringtonia speciosa
when its contents are quite fluid.
SUMMARY
(1) The inquiry is mainly directed to the conditions of seed-
coloration, to the How rather than to the Why (p. 368).
(2) Questions relating to the specially adaptive nature of the colours
of seeds are summarily dismissed on the ground that we are not
justified in selecting one character that happens to be conspicuous to
our senses, whilst ignoring the great number of other characters that
can make no such appeal to us (p. 368).
(3) After referring to the wealth of seed-colour displayed in a
typical native garden in Jamaica, the author cites cases of the develop-
ment and disappearance of seed-colours before the fruit is ripe or before
the seeds are exposed to view (p. 369).
(4) After it has been shown that as a general rule seeds colour in
the closed fruit, as illustrated in the case of berries, capsules, and
legumes, inquiry is made as to the stage in the history of the fruit in
which the coloration takes place, whether in the green, the ripe, or
the drying stage, or in all three of them. Though it is established
that coloration frequently takes place in the moist green and ripe
capsule, the subject is acknowledged to be a very difficult one,
especially as concerns the legume (p. 370).
(5) In this connection reference is made first to the experiment
of Lubimenko, in which the seeds of young leguminous pods were
exposed to the outer air by removing portions of the pods, and to the
conclusion drawn that for the normal development of the seed a con-
fined atmosphere of stable composition is needed (p. 373).
(6) The author then gives the results of his similar experiments in
the case of green capsules of Scilla nutans on the plant, the upshot being
that immature seeds exposed to the outer air by windows cut in the
fruit-walls developed normally, with the exception of their failure to
acquire the black colour of the resting seed. It thus became evident
that the seeds acquire their shining black hue only in the confined
atmosphere of the moist green capsule (p. 374).
SEED-COLORATION 401
(7) The conditions under which seeds colour in leguminous pods
and in capsules are discussed in detail, and the black and brown forms
of coloration, including black mottling, are especially dealt with.
After observing that the coloration, early shrinking, and hardening of
the seed and its coats are so conspicuously associated with the early
drying of the fruit, that the presumption in favour of there being a
causal connection is very strong (more especially in the case of legumes),
it is shown that this view is untenable. The results of experiment
demonstrate that these changes in the seed can take place under
conditions so humid that the drying of the fruit is precluded. In a
word, the regime involved in the coloration, early shrinking, and
hardening of the seed and its coats, both in the legume and in the
capsule, is that which is displayed by the colouring, shrinking, and
hardening seed in the moist berry. The seed colours normally in
moist fruits and continues the process notwithstanding the drying of
the fruit. In some cases, however, as in black mottling, the complete
coloration of the seed is interfered with by the fruit's drying (p. 375).
(8) The colours of unripe and mature seeds, that is, of pre-resting
and resting seeds, are then compared in legumes, capsules, and berries,
and the inference is drawn that unripe or pre-resting seeds are usually
white in capsules and green in legumes (p. 385).
(9) It is pointed out that the colour of the coats of the resting
seed in leguminous plants has but little connection either with the
colour of the coats of the pre-resting or unripe seed, or with the colour
of the embryo in the pre-resting and resting states ; but it is indicated
that with unripe leguminous seeds green embryos and green coats
usually go together (p. 389).
(10) The changes in colour which the green embryos undergo
when entering the resting stage and subsequently when germination
begins are then discussed in the cases of seeds of Poinciana^ Cassia^ and
Bauhinia. They all assume a pale yellow lifeless hue in the resting
seed, and, as illustrated by the seeds of Poinciana regia, display consider-
able lethargy in the waking up of the dormant embryo during the
germinating process. In some non-leguminous seeds, as with those of
Hura crepitansj the green embryo becomes decolorised and blanched
when entering the resting state (p. 391).
(n) The colour of the hypocotyl in leguminous embryos, as with
green cotyledons, is shown to be sometimes white and sometimes green
(P- 393)-
(12) It is observed that whilst the embryos of leguminous resting
seeds are usually pale yellow, green embryos are not uncommon in the
resting seeds of other orders (p. 394).
(13) With regard to white embryos in leguminous resting seeds, it
is remarked that since in genera like Phaseolus and Canavalia^ where
26
402 STUDIES IN SEEDS AND FRUITS
they occur, the coloration of the seed-coats varies greatly, there is no
connection between the two characters (p. 395).
^14.) The red seeds of leguminous plants are then discussed,
especially with reference to the conditions in which the red colour is
produced and to the changes caused during germination. Those of
Abrus precatorius, Adenanthera pavonina^ and Canavalia gladiata are
taken as examples (p. 395).
(15) It is shown that the long duration of the red colour of the
above seeds depends on the impermeability of their coats and on the
non-hygroscopic behaviour of the seeds (p. 398).
(16) The stages in the coloration of the seeds of Iris faetidissima are
described (p. 399)-
(17) The coloration of immature seeds whilst their contents are
still fluid and before the embryo is recognisable is remarked in the
cases of some monocotyledons (p. 399).
CHAPTER XVIII
THE WEIGHT OF THE EMBRYO
ANY discussion of the proportional weight of the embryo in A difficult
albuminous resting seeds must be surrounded by a host of
difficulties. The first question to present itself is concerned
with the utility of such a discussion, since, if we cannot bring
the subject into some sort of relation with other matters
affecting the seed, it would not be worth while following
it up. But if this seems feasible, we are at once confronted
with other difficult questions. Although not directly con-
cerned with exalbuminous seeds, we cannot ignore their close
connection with albuminous seeds. We must at the outset
select some standpoint for viewing this relationship, and much
depends on our answer to the query Which is the older
of the two ?
I suppose that on biological grounds there can be no doubt The
that the albuminous is the primal state ; but one has only to
watch a germinating seed bravely endeavouring to strike into
the soil, whilst its cotyledons still within the seed-case are
appropriating the albumen, to decide that the albuminous state
is the older condition. We here perceive the transition from
an albuminous to an exalbuminous state in actual operation,
the chief point of difference being that whilst the change, as
generally understood, occurs in the seed before it enters the
resting condition, here it takes place in the germinating seed
after the resting-state stage is passed. Our plantlet is now
doing what is often effected within the seed at an earlier stage
403
4 o 4 STUDIES IN SEEDS AND FRUITS
before the resting state is imposed. All exalbuminous seeds
have in a sense been once albuminous, and the distinction
which we draw between exalbuminous and albuminous seeds
mainly depends on whether the transition occurs before or
after the rest-period. The after-ripening of seeds must be
often concerned with the change from the albuminous to the
exalbuminous condition. That which happens in the Jasmine,
where the albumen is at first copious in the seed and dis-
appears when the seed is ripe for germination, occurs with
many other plants. It would be quite possible, for instance,
in the case of the Ivy (Hedera]^ as described in Chapter XIX,
to describe the seed as albuminous in its first stage and as
exalbuminous when about to germinate. The interposition
of the rest-period in the early portion of a plant's existence
is responsible for many false distinctions and many incorrect
comparisons.
Other diffi- Another difficult point has been already indicated. In the
resting albuminous seed, as is well known, the embryo may
exist in all stages, from that in which it is imperfectly differ-
entiated to that in which the plumular leaves are developed
and we have a perfect plantlet within the seed. Between these
two extremes all gradations occur. Then, again, we have often
genera with exalbuminous seeds and genera with albuminous
seeds in the same order. Thus with Sapotaceae, at first sight
the seeds seem very similar in structure. Yet the proportion
of albumen may vary in different genera, from that found in
AchraS) where it amounts to about 84 per cent, of the kernel's
weight, to its condition in Chrysophyllum, where it may range
between 20 and 40 per cent, in different species, whilst in
Lucuma there is none at all. Of the 222 families of angio-
sperms described in the System of Botany of Le Maout and
Decaisne, about 18 per cent, possess both albuminous and
exalbuminous seeds.
Dr Goebel in his Organography of Plants (English edition,
ii. 262) lays stress on the far-reaching nature of the changes
in the form of the embryo arising from the different modes of
THE WEIGHT OF THE EMBRYO 405
disposition of the food-reserve ; and one has only to refer
to Lord Avebury's volume on seedlings in the International
Scientific Series to become apprised of this fact. For example,
we have its disposition in the cotyledons, as in many leguminous
seeds ; its disposition in the hypocotyl, as in the Rarringtoni<e
and with some Guttiferae, and its disposition outside the
embryo altogether, as occurs with many plants. The embryo
in different resting seeds varies so much in its stage of develop-
ment and so much in its relation to the reserve supply of food
that one hesitates to consider the matter of its relative weight
at all.
However, one has only to observe that whilst over 100,000
Juncus embryos are required to make up the weight of a single
embryo of the Coco-nut palm, they are in relation to the
kernel more than 200 times as heavy, in order to perceive that
a study of the secondary relations involved in such measure-
ments may lead to some interesting conclusions. Whilst the
Coco-nut embryo is in an absolute sense one of the very largest
and heaviest amongst embryos of its kind, it is in a relative
sense, as compared with the kernel, one of the very smallest
and lightest. The subject from this standpoint seems to lend
itself for inquiry, and here again the principal instrument of
investigation is the balance, weight as a general rule connoting
size.
The estimation of the weight of the embryo in very small Method of
seeds, as in those of the Common Rush (Juncus\ is easier than Se^^h^t
it might at first seem to be. It soon became apparent to me of mute
that I could begin by ascertaining the proportional bulk and
the proportional weight of the embryo as part of the kernel in
a seed that could be easily examined, and that by a comparison
of the two results a constant error might be found which
could be applied in those numerous cases where, owing to
the use of the balance being impracticable, one is compelled
to rely on the proportional size of the embryo for the clue
to its weight.
As suiting my purpose the light brown seeds of dehiscing
4 o6 STUDIES IN SEEDS AND FRUITS
fruits of Iris Pseudacorus were chosen. A hundred embryos
were found to make up the weight of a single kernel ; and
since the kernel weighed 1*3 grain, this gave '013 grain as the
weight of the embryo. It was then ascertained that in point
of bulk about 85 embryos went to a kernel, which, interpreted
as weight, gave the weight of the embryo as -015 grain, which
is 1 6 per cent, greater than the actual weight determined by
the balance. It was then assumed that weight calculated from
relative size displayed an error of this amount, but, taking into
consideration the fact that the method is at its best crude, and
remembering that only approximate results could be looked
for, I decided to ignore it altogether and to accept bulk as
roughly indicative of weight.
As it was evident that in very small seeds one would have
to rely mainly on the bulk-data, the question arose as to the
method of obtaining them. My choice lay between making
my own seed-sections and utilising the materials offered by the
illustrations in The System of Botany of Le Maout and Decaisne
(English edition, 1873) ; and the last method was selected.
From the sections of seeds there figured I could procure the
requisite measurements, obtaining for myself, when needed, the
data for the relative thickness of the seed. But in the first
place I tested the method by comparing the results obtained
by estimations from the figures in the above-named work with
those supplied by actual measurements of the seed. They
came fairly close together in the case of the seeds of Iris
PseudacoruSj 85 embryos going to make up a kernel by my
own measurements of the seeds, and 75 according to the data
offered by the illustration of an Iris seed of the same type
in the general work. The seeds of the Elder (Sambucus
nigra), weighing only -05 grain, were then employed. Actual
measurements of a seed indicated that the embryo formed
about a tenth of the bulk of the kernel, whilst the data
supplied by the figure of the same seed gave the proportion
as one-twelfth.
Still smaller seeds, those of Aquilegia weighing only -03
THE WEIGHT OF THE EMBRYO 407
grain, gave similar proportions for the two methods, the size
of the embryo, whether obtained from the actual seed or from
the illustration, being about -%-Q of that of the kernel. In this
case the proportional weight of the seed-coats was taken as
one-third of the total weight of the seed, which left -02 grain
as the weight of the kernel. I was therefore dealing with an
embryo which weighed not more than * part of a grain.
From the case of the Aquilegia seed to that of the minute
seed of a rush (Juncus) the step was not a very difficult one.
Having found that about 5500 seeds of Juncus communis went
to make a grain, I had to allow for the weight of the seed-
coats, which, judging from the figures and from my own
examination of the seed, was relatively much less than with a
seed of Aquilegia^ so I placed it at about one-fifth of the seed's
weight. The weight of the embryo was then calculated to be
about one-tenth of that of the kernel, and from these data the
following results were obtained :
( Entire seed 35^ grain or -0000118 gramme.
Juncus communis < Kernel <; sVs -0000094
(Embryo ^ -0000009
In this manner, therefore, the minutest of embryos are
shown to be within reach of the balance. Whilst nearly
70,000 of the embryos of Juncus communis are required to make
a grain, nearly 200 of them placed in line will make an inch,
and nearly 8 will make a millimetre, the length of the embryo
being one-third that of the seed, which, according to my
measurement, is 0-4 millimetre long.
With these preliminary remarks I will now give in tabular
form the results of my observations on the weights of the
embryos of albuminous resting seeds in the case of more than
fifty plants. They are arranged in the order of the embryo's
relative weight as a portion of the kernel. The indications
supplied by such an arrangement are full of suggestiveness,
and are especially discussed in the remarks that follow the
table, as well as in the last paragraph of the chapter.
4 o8 STUDIES IN SEEDS AND FRUITS
THE WEIGHTS OF EMBRYOS IN ALBUMINOUS RESTING SEEDS.
(Palms are indicated by P. When a figure of the seed has been utilised, as in the
case of small seeds, L. is placed after the name, the System of Botany of Le Maout
and Decaisne being usually employed. See text before and after table for further
explanation. )
Weight of the Embryo.
Remarks. (S. entire seed ;
Actual weight.
As a
C. coats ; K. kernel.
part ol
the
Weights in grains. )
Grains.
Grammes
kernel.
P. Cocos nucifera .
2
129600
*A*
A ripe fruit of average
weight with mature
kernel.
P. Bactris ....
A
002160
rAo-
A dry fruit.
P. Cocos (schizophylla ?)
i
'012960
rTnnr
Tamus communis, L.
TTiW
'000015
1 000
S. '27 ; C. '02 ; K. '25.
P. Acrocomia lasiospatha
A
003240
TOTJ
A dry fruit.
P. Licuala grandis .
*
000810
yio
Mercurialis, L.
sA
'000013
TOTS
S. '125 ; C. '025 ; K. 'i.
P. Prestoea montana
&
'001620
*irr
A dry fruit.
Anona Cherimolia
TTD
'000648
T&T)
S. 8'o; C. 3-4; K. 4-6.
P. Areca Catechu .
i
'012960
TTT
A moist ripe fruit.
P. Elaeis guineensis
A
003240
S^TT
A dry fruit.
Anona reticulata
nW
'000648
~sfa
S. 4'o ; C. i'o ; K. 3'o.
P. Hyophorbe Verschafftii
A
'001296
*tar
A fresh fruit.
P. Mauritia setigera
'i
'097200
FOTT
A fruit beginning to dry.
P. Sabal umbraculifera .
v
'001296
TTO
A dry fruit.
P. Manicaria saccifera .
I
'064800
TiZT
ii
P. Oreodoxa oleracea
*
'001080
U^ff
()
P. Livistonia ....
A
'004630
T5TF
M
P. Caryota ....
'009260
T^U
A fruit beginning to dry.
Aquilegia, L. .
T^itTS
'000006
TO^O
S. '03 ; C. 'or ; K. '02.
Anona palustris .
TV
'000926
ri^
S. 3 '9 ; C. i '2 ; K. 27.
P. Oreodoxa regia .
A
'001620
rio
A dry fruit .
Dracaena Draco . .
A
'003240
T|B
S. 6'o; C. 0-2; K. 5-8.
Carex, L. .
5SOO
'000026
T^T)
S. '05 ; C. 'oi ; K. '04 ;
an average.
P. Cocos plumosa .
A
003240
nV^
Fruit partly dry.
Iris Pseudacorus
A
'000810
rJir
Seeds partly dry ; S. 2 'o ;
C. 0-7; K. 1-3.
Luzula, L.
irAl)
oooo 1 7
A
S. '03 ; C. 'oi ; K. '02.
Hedera Helix .
iV
"000926
A
S. '8; C. '07; K. 73.
(See Chap. XIX.)
Veronica, L.
rAff
000019
A
S. '013; C. '003; K. - oi.
Ricinus communis
A
006480
A
S. 27; C. 7; K. 2-0.
Papaver, L.
TTriflTF
000006
A
S. '0025 ; C. '0005 ;
K. '0020.
Canna indica
TTT
006480
TO"
S. 2-6 ; C. '6 ; K 2'o.
Jatropha Curcas
f
'025920
A
vS. i2'o ; C. 4'4 ; K. 7 '6.
Ravenala madagascariensis
i
012960
A
S. 5-5= C. 2-5; K. 3-0.
Sambucus nigra, L. .
*b
'000196
A
S. '05 ; C. '02 ; K. '03.
Rumex, L.
TSTT
'000260
A
S. '054 ; C. '014; K. '04.
THE WEIGHT OF THE EMBRYO 409
THE WEIGHTS OF EMBRYOS IN ALBUMINOUS RESTING SEEDS continued.
Weight of the Embryo.
Remarks. (S. entire seed ;
Actual weight.
As a
C. coats ; K. kernel.
part of
Weights in grains.)
the
Grains.
Grammes.
kernel.
Scrophularia, L.
WFTT
ooooio
TV
S. '002 ; C. '0005 ;
K. '0015.
Berberis, L. .
T$ir
"000648
rV
S. -14; C. -04; K. -i.
Anagallis, L. .
TBTTTT
'000026
A
S. '006 ; C. '002 ; K. '004.
Sparganium ramosum
T$T
000648
A
S. -ii ; C. -oi ; K. 'i
(fresh).
Saccoglottis amazonica
A
045360
A
S. 8-3; C. 1-3; K. 7-0.
Juncus, L.
^"8T*TF
'OOOOOI
iV
See p. 407.
Hura crepitans
l
'113400
i
S. 20 ; C. 6 ; K. 14.
Glaux maritima *
T*W
'000040
*
S. '007 ; C. '002 ; K. '005
Viola tricolor, L.
FTTT
'000108
i
S. '016 ; C. '003 ; K. "013.
Achras Sapota
TV
045360
S. 9-0; C. 4-8; K. 4-2.
Cassia t .
I
'064800
i
S. 8 ; C. 2 ; K. 6.
Ipomrea pes-caprse
4
032400
i
S. 37 ; C. 17 ; K. 2'o.
, , tuberosa
6
388800
4
S. 22-5 ; C. 4-5 ; K. i8'o.
Plantago, L. .
T& IF
'000216
k
S. "02 ; C. *oi ; K. '01.
Poinciana regia
Z
129600
i
S. 9'3 ; C. 4'3 ; K. 5'o.
Colubrina asiatica .
i
010800
S
~s
S. '60 ; C. '31 ; K. '29.
Chrysophyllum Cainito
5r%
362880
i
S. 12; C. 5 ; K. 7.
Exalbuminous seeds
...
1
* Proportions of the embryo of Glaux maritima from figure in Das Pflanzenreich,
iv. 237.
t This represents a mean result for three species of Cassia (fistula, grandis, marginata).
Here we have the weights of the embryos for about fifty- Remarks on
three species and generic types of albuminous seeds, of which
almost a third belong to palms. For reasons before implied, the
relative weight of the embryo in proportion to the kernel is
alone given. This is the only ratio that is generally applic-
able, it being apparent that the inclusion of the seed-coats in
the discussion would have but little significance in a series
comprising the seeds of palms, whilst the proportional weight
of the embryo with regard to the fruit would possess but little
value, if only for the reason of there being many-seeded as
well as single-seeded fruits.
If required, the proportional weight of the embryo with
reference to the entire seed (kernel and coats) can be
4 io STUDIES IN SEEDS AND FRUITS
determined for any ordinary seed by making use of the data
given in the last column of the table. Thus, in the instance of
Canna indica, the embryo is given as -^ of the weight of the
kernel ; but by employing the data given for the entire seed
we obtain a proportional weight of ^-g. Then, again, if further
particulars relating to the palm-embryos are needed, the weight
of the kernel can be readily calculated from the results given
in these columns, and by referring to Chapter XIV the weight
of the entire fruit can in most cases be found. For instance,
in the case of ripe coco-nuts, where the kernel makes up
about one-fourth of the weight of the fruit, the total weight
for the fruit illustrated in the table would be about 17,500
grains, and the relative weight of the embryo would be there-
fore about -g^Vo' Coco-nuts vary so much in weight both in
their several stages and in their different varieties that the
same result can be scarcely looked for. So again with the dry
fruit of Licuala grandis^ since the embryo weighing -^ grain is
equal to -5-^ of the weight of the kernel, we obtain 6*2 grains
as the kernel's weight. In a table in Chapter XIV the average
weight of the entire fruit is stated to be 10 grains, from which
the relative weight of the embryo may be placed at -g-^ of the
fruit's weight.
Another important point is that we are here dealing with
the embryos of resting seeds. In most cases this is a seed
that has dried, spontaneously on the plant ; but with palms
several other considerations arise, and it is often more than
probable that a palm seed which has completed the normal
drying process has lost its capacity for reproducing the plant.
In some palm seeds it is likely, as in the case of that of the
coco-nut, that during the ripening of the kernel the oil increases
as the water diminishes.
The embryos With nearly all the palm seeds experimented upon the
embryos belonged to dry fruits and were more or less
shrunken. In a few instances, as with Cocos nucifera, Mauritia
setigera, and Areca Catechu^ the fruits were ripe and still moist,
the kernel reaching maturity after the husk had commenced to
THE WEIGHT OF THE EMBRYO
411
dry. According as we take the ripe moist fruit or the fruit
that has completed its drying process, the proportional weight
of the embryo as concerns the kernel varies greatly. This is
due to the fact that whilst the albumen of such a ripe fruit
usually loses when dried about a third of its weight, the
embryo loses about two-thirds. The effect of this, as shown in
the results given below, is to halve the relative weight of the
embryo as compared with the kernel in the spontaneously
dried fruit. Thus with Cocos nucifera the embryo is grVg- of
the weight of the kernel in the ripe fruit and ^g-g- in the
dry fruit many months old, though it is more than doubtful
whether the shrunken embryo in the last case would retain its
vitality.
TABLE SHOWING THE Loss OF WEIGHT, WHEN DRYING SPONTANEOUSLY,
OF THE ALBUMEN AND EMBRYO OF THE RIPE SEEDS OF PALMS,
AND ITS EFFECT ON THE PROPORTIONAL WEIGHT OF THE EMBRYO.
Loss of weight.
Proportional weight of the
embryo as a part of
the kernel.
Albumen.
Embryo.
Ripe seed.
Dry seed.
Cocos nucifera
Acrocomia lasiospatha
Mauritia setigera .
Areca Catechu
Oreodoxa oleracea
Prestcea montana .
Licuala grandis
33 per cent.
4 ,,
3
28
66 per cent.
66 per cent.
66
70 per cent.
60
TTST
ufa
~S$T!
T&T
TT^TV
fiff
^ir
2&TT
It is thus seen that the discussion of this subject as concerns
the palm embryo presents serious difficulties. Every type
of palm seed would probably have its own regime, and we
are for ever thwarted by the interposition of the rest-period
and its results. An important contrast is brought out by
observing the behaviour of different embryos when placed
in water. In the ripe coco-nut the embryo fills its cavity The embryo
> i r j of Cocos
and is more or less in a state or saturation as regards its nuc if era .
water-contents, since on being placed in water its weight
4 i2 STUDIES IN SEEDS AND FRUITS
remains unchanged or is increased only 2 or 3 per cent.
As the fruit proceeds with its drying the albumen and the
embryo lose weight together during the first few months.
The weight of the embryo, originally about 2 grains, is reduced
to i '8 grain after three months and to 1*5 after six months,
the embryo still almost filling its cavity and showing only
a slight collapse at the sides, whilst its weight is only increased
by 14 or 15 per cent, when placed in water. There is but
little marked shrinkage in the form of the embryo, a result
that is certainly due to the increase in its oily constituents ;
and we have already seen in Chapter XIV that as the kernel
ripens the oil increases in amount. It is only with very old
lifeless coco-nuts that we would expect to notice great shrink-
age of the embryo.
Thus the behaviour of the embryo of the coco-nut is
evidently peculiar. When comparable with those of other
palms in the early mature state of the fruit it is, as shown in
the table above, full of water, losing two-thirds of its weight
when drying spontaneously in the detached condition, and
returning to its original weight when resting on water. But
in the later stages of maturation, when the oil in the kernel
increases in quantity and the fruit is drying, the embryo
becomes more oily, and loses but little water when detached
and allowed to dry, and only increases its weight slightly
when placed on water. This peculiarity is also brought out
in the next table.
"he embryos Now, the embryos of most of the other palms examined
behaved very differently, as shown in the results below
tabulated. Whilst with the fresh ripe fruits the embryo
usually fills its cavity and is more or less in a state of satur-
ation, it shrinks considerably as the fruit dries, so that in
the course of two or three months it usually presents itself
as a more or less shrivelled object but partly filling the cavity.
Such shrunken embryos, when placed in water, double their
weight in a couple of hours and regain their original form.
The shrinking of the embryo may even be evident in ripe
THE WEIGHT OF THE EMBRYO 413
fruits that have been gathered only two or three weeks. This
happens with the embryos of Mauritia and Cocos plumosa.
TABLE SHOWING THE CONDITION OF PALM-EMBRYOS IN FRUITS SOME
TIME AFTER GATHERING, AND THEIR BEHAVIOUR WHEN ALLOWED
TO REST ON THE SURFACE OF WATER.
Period since
gathered.
Condition of the
embryo.
Increase of
weight when
placed on water.
Oreodoxa regia
7 weeks
Rather shrunk
40 per cent.
, , oleracea
8 months
Much shrunk
130
Sabal umbraculifera
16
Shrunk
1 60
Acrocomia lasiospatha
12 ,,
Somewhat shrunk
IOO
Bactris
2 ,,
A little shrunk
Cocos nucifera
6
Slightly shrunken
1 5 per cent.
,, plumosa
2 weeks
Much shrunk
IOO
, , schizophylla
2 years
Very much shrunk
200
Areca Catechu
5 weeks
Greatly shrunken
200
Licuala grandis
1 8 months
Much shrunk
IOO
Prestcea montana
4
Greatly shrunk
250
Hyophorbe .
* ,,
Shrunk
Elseis guineensis
2
Rather shrunk
90 per cent.
Livistonia .
2 years
Much shrunk
Caryota
2 months
Rather shrunk
Although in four cases the behaviour of the shrunken embryo in water was not tested,
it is evident that the same effect would be produced.
The gain of the shrunken embryo in water represents
the original loss in the drying process, the embryo acquiring
its full outlines and approximately its original size and weight
in the moist ripe fruit. It should be allowed to rest on the
surface of the water for a couple of hours, when it usually
ceases to gain weight. The albumen of the seed containing
the shrunken embryo takes up much less water. Thus, to
take the behaviour of a Sabal seed sixteen months old, whilst
the albumen, when placed in water, added only 33 per cent, to
its weight, the embryo increased its weight by 160 per cent.
This is consistent with the principle before stated that when
a ripe palm fruit dries spontaneously the albumen loses about
one-third of its weight and the embryo about two-thirds.
That palm seeds retain their vitality but a short time
would seem to be the rule. Mr Hart, late Superintendent
4 i4 STUDIES IN SEEDS AND FRUITS
of the Botanic Gardens at Trinidad, tells me that the limit
for Acrocomia, Oreodoxa, Sabal, Thrinax^ etc., when the fruits
are protected from the sun and rain, would be from three to
six months, whilst for Mauritia, he says, the limit would be
only a week or two. Unless the embryo increases its oil
during its loss of water in the drying process its longevity
would seem to be but slight. The reciprocal relation between
oil and water in the embryo is a matter of importance for
certain palms. Thus I would assume that the oily embryo
of El<eis guineensis would possess a greater staying capacity than
the watery embryo of Areca Catechu^ though in both cases
marked shrinkage might take place in the case of the embryo
removed from the fresh ripe fruit. Let the fruits remain on
the palm and the difference in the behaviour would assert
itself ; but if both fruits are allowed to dry in the detached
condition, their embryos will probably be similarly shrunken.
One would only look for the contrast in the condition of the
embryos in the case of fruits that have dried on the tree.
Speaking generally, I would consider that palm seeds where
the albumen is ruminate, as with Areca^ Caryota, and Thrinax y
would preserve their vitality for a much shorter period than
where it is homogeneous, as in the majority of palms, the
more rapid drying of the ruminate albumen being promoted
by its peculiar structure.
One may mention in passing a fact which, though familiar
to the students of palm fruits, may be new to some of my
The water of readers. The water filling the cavity of the fruit is not
peculiar to Cocos nucifera (Coco-nut), but occurs with other
palms of the same tribe of the family, at least in the immature
condition of the fruit, and in fruits so small that 300 or 400
of them are needed to make up the weight of a single coco-nut.
Thus in Bactris the hard black shell or endocarp of the ripe
fruit is soft and white in the immature fruit. The cavity
within the shell of the young fruit is lined by jelly-like
albumen and is quite full of water. As maturation proceeds
the albumen solidifies and increases so as ultimately to fill
THE WEIGHT OF THE EMBRYO 415
the cavity, leaving only traces of the original central hollow.
The narrow fissure-like central cavity found in the albumen
of moist ripe fruits of other genera of the same tribe of
palms, such as Acrocomia and El<eis^ gives an indication of
a similar history of the young fruit. I may remark that even
the large cavity of the coco-nut may be sometimes nearly
obliterated. The kernel is so thick in a variety growing in
the Moluccas that there is scarcely any central space (Tropical
Agriculturist for 1833).
It would be possible to greatly lengthen this chapter,
but I have approached the subject mainly as a preliminary
to the discussion of the rest-period in the next chapter.
Measurements of weight may have but little meaning in
themselves, but they acquire a significance when we arrange
them in order, as in the general table before given. The
indications of the separate seeds are full of suggestiveness.
Here we have a series of resting seeds, beginning with those
where the embryo constitutes only 20 1 00 of the weight of the
kernel (the other 1999 parts belonging to the albumen) and
ending with seeds where the embryo has appropriated all the
reserve-food, storing it either in its cotyledons or in other
parts of its substance. The series speaks eloquently of the
true relation between an albuminous and an exalbuminous
seed. But it is as concerns the rest-period of seeds that Therest-
the story of these figures has its most important lesson for
us, nature having imposed it on the young plant at all
stages of its early development. It is around the mystery
of the resting seed that the discussion in the following chapter
will chiefly centre.
(i) Any discussion of the weight and size of the embryos of rest-
ing albuminous seeds must be beset with difficulties. Foremost comes
that concerned with the relation between the albuminous and
exalbuminous state, and it is assumed that the first is the primal
condition. Then there are the disturbing facts that not infrequently
416 STUDIES IN SEEDS AND FRUITS
the same order possesses plants with both albuminous and exalbuminous
seeds, and that the rest-period has been imposed on the embryo in
very different stages of its development (p. 403).
(2) The method of measuring the weight of minute embryos is
then discussed, and it is shown that even those of Juncus communis, of
which nearly 70,000 go to a grain, are not beyond the reach of the
balance (p. 405).
(3) The author then gives his results for the weight of embryos in
the case of more than fifty kinds of plants, of which nearly a third
belong to palms. The only weight-ratio of the embryo that is given
is its proportional weight as a part of the kernel, though in the case of
ordinary seeds data for estimating other ratios are added. It is con-
sidered that the embryo-kernel ratio is the only one that is generally
applicable ; and in the table the results are arranged in order, beginning
with those seeds where the embryo forms a very small proportion of
the albumen and terminating with the exalbuminous seed, where the
albumen has all been appropriated by the embryo (p. 408).
(4) The embryos of palms are specially dealt with, and though
the subject has many difficulties, some broad results follow from the
author's observations. In the first case it is shown that as a rule the
embryo shrinks in the drying fruit about twice as much as the albumen,
and that in consequence its proportional weight with regard to the
kernel is much less in the dry than in the moist fruit (p. 410).
(5) Then stress is laid on the fact that this great shrinkage of the
embryo in the drying fruit usually occurs in the first few weeks or
months, and that for this reason the seeds of palms could scarcely
be expected to retain their vitality for a long period. Facts are
given which show that although the period may be as little as two
or three weeks, it does not generally exceed six months. On account
of rapid drying being favoured by their peculiar structure, it is con-
sidered that ruminate seeds of palms would possess the least staying
power (p. 412).
(6) Allusion is made in passing to the fact that the coco-nut is not
peculiar in possessing in the unripe condition a large cavity filled with
water, the fruits of other genera of the same tribe of palms being thus
characterised, even in cases where they are only an inch in size when
full-grown (p. 414).
(7) The author concludes with the remark that he has approached
the subject of the weight and size of embryos mainly as preliminary to-
the discussion of the rest-period in the next chapter.
CHAPTER XIX
THE REST-PERIOD OF SEEDS
IF everything comes from the egg, it is certain all lines of
biological investigation lead back to it, and thus it is that in
the resting seed our interests converge towards that point in a
plant's life. Many botanists of eminence have dealt with this
matter, and the salient facts must be familiar to my readers.
There are, however, certain aspects of the subject which have
come more particularly under my notice ; and ever since I studied
the vivipary of Mangroves, like Rhizophora and Bruguiera^ in
the Pacific, twelve to fifteen years ago, the matter of the rest-
period of seeds has been frequently before my mind.
The rest-period represents a break in the continuity of the A break in
young plant's existence. As Goebel well puts it, the seed here O f "young 1 7
submits to an interruption in its development ; and so it is P lant ' s llfe -
that the real mystery of the seed lies not so much in the
resumption of active vitality implied in germination as in the
suspension of its vitality. That singular phase in a seed's
life, the entering into the rest-period when it is quite able
to proceed continuously with its growth and to go on to
germination, is the true mystery. The potential vivipary of
plants I hope to establish later, meaning thereby the inherent
ability of the embryo to proceed with its growth.
But in the first place it is necessary to acquire a correct The degree
notion of the prevalence of the resting habit in seeds, since we valence of
are apt to invest this character of seeds with a universality that the resting
. j. 1 ... habit in
it does not actually possess and with a persistence that it can seeds.
417 27
4 i 8 STUDIES IN SEEDS AND FRUITS
scarcely claim. Since much of the substance of the two follow-
ing pages will be found in the text-books, it will be sufficient
to refer to the works consulted at the end of the chapter.
Goebel points out that whilst with Ferns, Lycopods, and
Equisetums there is no rest-period, in Seed Plants with few
exceptions the embryo experiences sooner or later an interrup-
tion of its development which is resumed in germination. In
reality, though the pronounced exceptions are few, there are
many in degree, as is indicated by the transient nature of the
rest-period in a large number of plants and by the prevalence
of after-ripening, a term applied to the growth of the embryo
in the resting seed before and after detachment from the
parent plant. As regards the shortness of the period, let us
take our own forest trees. The seeds of the Oak, Beech, Elm,
Poplar, Horse-chestnut, Maple, Fir, etc., have, as is well
known, a very transient germinative capacity, as a rule only
preserving this power until the next spring, and even then
usually requiring to be planted soon after gathering. Probably
not a few of them, when their seeds germinate during a mild
autumn, supplement the short rest-period within the seed by a
period of repose outside the seed, remaining stationary during
the winter under the protection of the fallen leaves, and doing
little more than protrude their radicle an inch or two. This
capacity in the case of acorns is alluded to later on in this
chapter.
Many other seeds are known to behave similarly. Thus,
those of Oxalis and Salix fail usually after a few weeks or
months. Professor Ewart strikes the true note when
he remarks that in very many cases seeds are very intolerant
of even ordinary air-drying. According to De Candolle,
the seeds of most Rubiaceae, Myrtaceae, and Lauraceae lose
their germinative capacity soon after detachment from the
mother plant. The seeds of the Palmaceae also often retain
this capacity but a few months. In reply to a letter, Mr Hart,
late Superintendent of the Botanic Gardens in Trinidad, tells
me that those of Oreodoxa, Sabal, Thrinax, Acrocomia^ Attalea,
THE REST-PERIOD OF SEEDS 419
etc., will, if kept in a protected position, maintain their vitality
for from three to six months. If, however, there is an excess
of atmospheric moisture on the one hand, or drought on the
other, the time is much shortened. Some seeds of palms, he
adds, like those of Maurifia, will not keep more than a week
or two. Tropical seeds in general, according to Mr Hart, are
as a rule possessed of a very fugitive vitality. To keep seeds
in stock is, he says, an absurdity, and the only practical rule
is to clean partially and sow at once for the best success.
It is thus evident that the rest-period must be often a
transient feature with the seeds of many plants. Not only is
this the case, but there are many plants, as already indicated,
where the seeds experience after-ripening, the immature embryo Theafter-
of the resting seed continuing to grow up to the time of ger- ^^^ ng
mination. Such seeds, as Ewart observes, have apparently no
rest-period. Amongst examples given by Goebel and others
are those of Anemone^ Corydalis, Crinum, Ranunculus Ficaria,
Eranthis hiemalis, Gnetum gnemon^ Utricularia, etc. ; but the same
may be inferred of numbers of other plants where the embryo
is immature or but slightly differentiated, such as Cuscuta^
Qrobanche, Monotropa, Balanophore<z, etc., named by Kerner, and
Stylidium, Gagea^ and Erythronium, suggested by Ewart.
But in this matter we can make a much wider cast with
our net. After-ripening must often be counted upon by the
agriculturist and the gardener. They know that certain seeds
cannot be forced. It is the experience of the gardener, says
Kerner, that many seeds have to mellow or ripen before
germination ; and he reminds us that in many cases seeds
germinate in the spring under apparently much less favourable
conditions of temperature and moisture than they enjoyed in
the late summer and autumn of the previous year, when they
were first detached from the plant.
There is another familiar feature in connection with resting The varying
seeds which has been already implied, namely, the great varia- development
tion in the degree of development attained by the embryo
when entering the resting stage. In some the embryo is in ing seed
4 2o STUDIES IN SEEDS AND FRUITS
different stages of incompleteness. In others it is ready to
germinate. No one has stated the matter more clearly than
Goebel, and to no one are we indebted for a more authoritative
discussion of the subject. It is indeed quite a commonplace
feature in seed-life, and I hesitate to add the results of my own
observations on a matter long recognised. The data supplied
by Goebel in his Organography of Plants (ii. 248-254) supply
a most important lead for the investigator. Differences of this
kind we are wont to associate with a genus or a family, but
here we learn that, as in Anemone and Utricularia^ they may be
found within the limits of a species and even in the same
individual.
We are told that we can only conjecture about the causes
of this behaviour ; but the problem restricted to such narrow
limits presents an inviting field for the investigator. As will
be subsequently pointed out in other plants, the differences
in the degree of development of the embryo in these cases is
probably associated with the displacement of the period of
fruit-maturation as regards the seed. Thus, I would suppose
that when the embryo in the resting seed is able to produce its
cotyledons and even its first leaves, the fruit is much later in
maturing than when the embryo is merely an " unsegmented
acotyledonous body." We should then have to inquire into
the causes of the postponement or acceleration of the matura-
tion of the fruit with reference to the seed and its embryo.
The But before discussing this view of the matter I will adduce
inherent further evidence in support of the contention that embryos,
dispensing^ whatever may be their stage of development in the resting
with the rest- seed, are inherently able to continue the growth suspended
period. ... J . f . . . . . . /
through the intervention or the rest-period. This is or course
implied for many plants in the after-ripening of their seeds
and in the occasional premature germination of seeds on the
plant during exceptionally humid weather ; but I desire now
to show that all seeds, or rather their embryos, possess an
inherent capacity of dispensing with the rest-period. That the
embryo of an albuminous seed is able to continue its growth
THE REST-PERIOD OF SEEDS 421
after removal from the seed was long ago established by Van
Tieghem in the cases of Maize and Mirabilis (Nobbe, pp. 310,
31 1). Here, however, the resting seed was concerned ; and it
is more to the point to establish it for the embryo removed
from the seed before drying and shrinkage begin.
I found that embryos of Iris Pseudacorus* removed from Detached
r 11 i j embryos of
their bed or albumen in the moist, uncontracted pre-restmg ins Pseuda-
seed and then placed in water, increased their length in a few corus -
days from 4 to 7 millimetres and displayed the plumular
nob. The progressive growth of the embryo as the fruit
grows and matures is in this plant very evident. Whilst the
seed maintained much the same dimensions (7 millimetres),
I obtained the following results for the growth of the embryo
in different stages of the fruit's development :
Immature fruit . . . embryo 1-5 mm. long
Ripe fruit before dehiscence . 2 2'5
Fruit beginning to dehisce . . 34
With the object of inhibiting the rest-period and inducing Experiments
, J , . , T i j inhibiting
pre-restmg seeds to proceed at once with germination, 1 placed the rest-
at different times a number of seeds of Iris Pseudacorus, Vicia peno *
septum, Arenaria peploides, and Quercus Robur under favouring
conditions in the moist, uncontracted state and obtained success-
ful results. Thus, after keeping some of the freshly gathered,
ripe, non-dehiscing fruits of the Iris in wet moss under warm
conditions (6o-7O F.) between ten and fourteen days, I found
that the drying of the fruits and seeds had been prevented and
that some of the seeds were germinating. The full-grown,
soft, uncontracted seeds taken from the green legumes of Vicia
septum behaved in the same way under the same conditions of
experiment. In four or five days they commenced to germinate,
and in five days the seedlings were half an inch long. The
white, soft seeds from the green capsules of Arenaria peploides
responded to my experiments precisely in the same fashion.
So also with Quercus Robur, it is not difficult to procure the
rapid germination of ripe acorns in September and October.
422 STUDIES IN SEEDS AND FRUITS
If fresh green acorns of full size and still vitally connected
with the cupule are placed in wet moss under warm conditions,
some of them will be found germinating within a week.
Nature's hint The germinative capacity of so-called unripe seeds does
gardener. not seem to have been fully appreciated by foresters, gardeners,
and horticulturists, the advantages to be derived from dispens-
ing with the rest-period being obvious. As subsequently
shown, nature offers us some valuable suggestions in this
direction in the case of the Oak. Many plants must afford
similar indications. Thus Pfeffer points out (ii. 205) that the
seeds of Senecio vulgaris and Stellaria media can germinate as
soon as they are ripe. Take again the soft, scantily protected
seeds of Pithecolobium filicifolium, the Bastard Tamarind of
Jamaica. They germinate a few days after falling from the
tree, or else lose their vitality altogether.
The causa- The causes of the phenomena displayed in the resting of
tion of the , , irii-ii>i-ri-
rest-period, seeds must be sought tar back in the plant s lire-history, not in
the seed alone, but in the seed as it depends on the fruit, and
in the fruit as it depends on the parent plant, and in the parent
plant as it responds to its conditions of existence. Therefore,
in dealing with the causation of the rest-period, we should
proceed in this order of investigation : the seed, the fruit, the
mother plant, and, lastly, the conditions. Yet it is at first
requisite to distinguish between the general causes that
determine the suspension of growth and the special influences
that determine the stage of development of the embryo at
which the rest-period is imposed. Any discussion of the
general causes must necessarily begin with an inquiry into
the influence of the fruit, and be then extended to the influence
of the parent, and then back to the conditions. Being un-
prepared to venture into such a wide field of investigation,
I will confine my remarks to the influence of the fruit, and
that only in an illustrative fashion.
The influence The biological disconnection of the seed indicated by the
of the fruit __ r <. . -, 1 i V
shrivelling or the runicle is proximately determined by the limit
of the fruit's vitality. The fruit dries, the funicle shrivels up,
THE REST-PERIOD OF SEEDS 423
and the rest-period begins. In other words, the fruit dies and
the seed lives, or rather it retains the potentialities of life. In
Chapter XIII I have dealt with the different behaviours of
the legume and the capsule as regards dehiscence, the first
dehiscing after drying is nearly or quite complete, the second
before drying commences or in its earliest stage. As the result
of these changes, the seeds shrink and harden rapidly when
exposed in the drying, dehiscing capsule, and less rapidly, but
not less effectually, in the drying but still closed pod.
If it were not for the drying of the fruit there would be
no reason why the soft seeds in the moist living fruit should
not proceed continuously with their development and dispense
with the rest-period altogether. In theory this should be
brought about by preventing the drying of the fruit. In
practice actual experiment has shown that this can be arranged,
as I have done with different fruits of Vicia^ Arenaria^ Quercus y
and Iris, by placing the fruit in moist, warm conditions when
in the full-grown living state. Under such circumstances the
capsular valves separate, whilst the legume decays rather than
dehisces, and the seeds will be found germinating in a week or
two without having experienced any pronounced check in the
development of the embryo.
But these are not the conditions usually presented in
nature. The capsule dehisces and dries, whilst the legume
dries and dehisces ; and the further development of the
embryo is arrested by the resulting shrinking and hardening
of the seed. On the assumption that the continuous growth
of the embryo-plant is the primal normal condition, there is
an obvious lack of co-operation or co-ordination here, since
experiment is able to arrange for the working together of the
conditions so as to ensure the uninterrupted growth of the
embryo. There is a lack of co-ordination in the capsule,
because the seeds are exposed in the moist fruit before the
embryos can lead an independent existence. There is a lack
of co-operation in the legume, because the pod begins to dry
before the seeds can sprout.
4 2 4 STUDIES IN SEEDS AND FRUITS
The rest- The rest-period therefore represents the failure of co-
fro^th? 111 * 8 operation between the parent, the fruit, and the seed. Over
failure of co- both seec j an( j f ru it hangs the fate of ultimate detachment
ordination of . .
the fnu't and from the parent, and according as there is concurrence or not
we get a viviparous or a resting seed. Successful co-operation
ensures not only that before the fruit begins to dry the seeds
are ready to germinate, but also that the germinating seed
should quickly find suitable conditions for further growth,
either by the timely fall of the fruit or by the liberation of the
germinating seed. But even here in the great majority of
cases germination on the plant takes place in a dying or
decaying fruit. Nature is seen at her best in the co-ordination
of the growth forces of the fruit and the seed in those plants,
like the Mangroves (Rhizophora and Bruguiera), where the
fruit still lives and the seed still grows, until at length the
seedling drops from the mother plant. This is the truest
form of vivipary.
But to return to the question of the lack of co-operation
between the seed and the fruit in the legume and capsule,
there is not much significance in the mere statement that
dehiscence occurs early in the capsule and late in the legume.
But there is a good deal of meaning when, viewing the
possibilities of vivipary, we state that dehiscence takes place
too early in the capsule and too late in the legume. If vivipary
took place in the capsule or in a legume, it would be under
the moist conditions illustrated in my experiments, where
soft, uncontracted pre-resting seeds were induced to germinate
without entering the resting stage. But in the capsule nature
defeats such an end by bringing about the early dehiscence of
the living fruit and the rapid drying of the exposed seeds.
In the legume nature would usually render such an event
impossible by bringing about the failure in the living but still
closed pod of the connection between the parent and the fruit.
The pod dries, the f unicle shrivels, the seed shrinks and enters
the resting stage, and last of all the fruit dehisces. Regarded
from the possibility of vivipary, this therefore is the significance
THE REST-PERIOD OF SEEDS 425
of the early dehiscence of many capsules and the late dehiscence
of the legume. For the continuous growth of the embryo,
which we assume to be nature's primal condition, the opening
of the fruit is wrongly timed in both cases, too early in the
one, too late in the other.
Let us take a conspicuous example of the ushering in of The case of
the rest-period in the case of the seeds of a ligneous legume regia.
like that of Poinciana regia. In the chapter on seed-coloration,
I have already described the remarkable changes which the
embryo of these seeds undergo when entering the resting
stage and when resuming active life and growth in the
germinating process. The embryo of the large, soft pre-
resting seed in the green and living pod is a plantlet full of
vitality with green cotyledons and green, partially unfolded
plumular leaves. When the fruit begins to dry the green
hue of the embryo disappears. The plumule folds up its
tiny leaves, and the rest-period commences.
The closing in and the cutting off from the external world
of the soft green respiring seeds of Poinciana regia seem
almost tragical, and one marvels at the fine adjustment which
allows these unresistant seeds to hold their own when every-
thing is hardening into tough wood around them. Let one
of the seeds fail in its early stage and the ligneous tissue
invades its area and occupies its place. What concerns us
here is that when the embryo loses its green hue, as the tissues
harden around the seed, it ceases to respire, and with its
vitality completely suspended it becomes buried in a hard
woody fruit that dehisces but tardily. In one's ignorance one
almost doubts the wisdom of such a suspension of active life
in the warm genial climate which this tree enjoys, since the
embryo has already advanced considerably in its growth and is
well able to proceed with its development.
Coming to the special influences that determine the stage The special
of development of the embryo when the rest-period begins, determinin
one may observe that the great variation displayed by the
embryo in this respect ought to be associated with correspond- period.
4 26 STUDIES IN SEEDS AND FRUITS
ing variations in the period of the fruits' maturation relatively
to the seed. If the fruit matures early and dries quickly the
embryo will not have reached the same stage of development
when the rest-period begins as when the fruit matures and
dries late. Where the fruit reaches the limit of its growth
far in advance of the seed, we might expect the embryo
to be small and but partially differentiated. Where the
fruit is not so advanced in growth, the embryo would be
much more developed when the suspension of vitality sets
in. Where matters are reversed and the embryo grows
quicker than the fruit-case, as in Avicennia^ the plant is
viviparous. Here, however, germination is associated with
the rupture and death of the fruit-envelopes. The truest
form of vivipary, as already observed, is seen in RMzopkora^
where the fruit still lives and the seed still grows, the
young plant remaining for a long time attached to the
parent.
It lies with the future inquirer to ascertain how the mother
plant through the fruit determines the stage at which the
rest-period is to be imposed on the embryo in the seed. Over
both seed and fruit, as previously remarked, hangs the fate of
ultimate detachment from the parent ; but this fate may be
avoided if the two co-operate so that when the fruit is ripe the
seeds have already begun to germinate. The seed depends on
the fruit and the fruit on the parent plant ; and since the
parent has its part to play in determining the relation of
growth between the seed and its fruit, it follows that it has the
first word to say in shifting the plane of the rest-period. I
may perhaps be allowed to suggest to some investigator that
he should inquire into
(a) The relation between the stage of development acquired
by the embryo in the resting seed and the time of
maturation of the fruit ;
() The relation between the early and late maturation of
the fruit (relatively to the seed) and the conditions
influencing the mother plant.
THE REST-PERIOD OF SEEDS 427
The problem, however, is an extremely complex one. A
method of approaching it is indicated in Chapter XIV, where
it is shown that two types of fruits can be differentiated when
we deal with the proportions of parts for the successive stages
of the fruit, as tabulated on p. 303. But this ignores the
transition from the albuminous to the exalbuminous state of
seeds, which involves a factor of paramount importance, and
one that carries us back to a very early state of the seed's
development. The whole subject will acquire a very com-
plicated character when we introduce this consideration into
the discussion.
A chance observation in May 1908 led me to suspect that The winter
the embryo of the seed of the Ivy (Hedera Helix) grew con- fhe embryo
tinuously through the winter and that germination occurred
without any rest-period in the spring. My suspicion was to plant
some extent confirmed when I found early in June that many
of the embryos had nearly doubled their length since the last
observation, and that some seeds were germinating within the
fruit on the plant. However, the actual growth of the embryo
in the winter had yet to be established. To this end my
sister, Mrs H. Mortimer, made periodical collections of the
berries at Redland, Bristol, during the winter 1908-9 ; and
on my return to England from the West Indies in the spring
I made use of these materials, the principal data obtained from
them being incorporated in the table subjoined. The behaviour
of the embryo in the spring was observed by me during the
four years, 1908-11.
It will be seen from the results tabulated on p. 428 and The growth
from the accompanying figures that the berries increased embryo of
gradually in size from the beginning of November 1908 to the jjj^jf upt<
latter part of January 1909, the green colour giving place to a
blackish hue and the maximum growth corresponding to the
complete blackening of the fruit. The increase during this
period of the solid constituents of the growing fruit as the
water-percentage diminished is especially noteworthy. Up to
January also the seeds grew with the fruit, their increase in
428
STUDIES IN SEEDS AND FRUITS
OBSERVATIONS ON THE GROWTH DURING THE WINTER AND SPRING OF
THE FRUITS, SEEDS, AND EMBRYO OF THE IVY (HEDERA HELIX).
(Weights in grains and lengths in millimetres.)
Moist fruit.
Air-dried seed.
Embryo of moist seed.
Loss of
weight
Colour.
Weight.
Weight.
Length
after
soaking.
Length.
Pro-
portion
of bulk
of moist
Colour.
of the
air-
dried
fruits.
Remarks.
seed.
1908.
Nov. 9
Green
i '69 grs.
06 gr.
4*5 mm.
07 mm.
i%
White
79%
i
M
2-86
5' >t
I- 5
i'5%
M
79%
Dec. 3
4*02 ,,
2 ,,
5'5 t>
1-6
'5%
it
76%
,, 17
Blacken-
4'9 6
24 M
6'o ,,
2-0 ,,
2-5%
7i%
ing
1909.
Jan. 9
Black
5 '44 ,,
'34 ,
6-0
2'2 ,,
3-o%
PI
65%
> 24
11
5 '5 n
"35
7'o t>
2'7
4-o%
,,
63%
Feb. zi
11
4*10 .,
36
6'7
2'5
3'5%
60%
Mar. 19
4*02
"34
6'3 ,,
2'3 >
3'5%
ii
61%
Some seeds
1909.
germinat-
Apr. 20
4'5 ,i
i%
Green
(57%)
ing on the
May 6
...
6-0
20%
ii
plant on
May 6.
1910.
Mar. ii
...
2'0
White
On May 22
Apr. 2
...
2'5
91
some seeds
., 8
May 3
3'
4-0
...
II
germin a t-
ing on the
,i 22
5'o
Green
plant.
Explanation. The observations of November 1908 to March 1909 were made from
collections obtained from the same plant by Mrs Mortimer at Redland, Bristol. Each
sample, consisting of from forty to sixty berries, was weighed at once, and subsequently
weighed and examined by me when the drying was complete some months after.
The other observations were made by me from fruits gathered at Salcombe in South
Devon.
In the case of the Bristol fruits the data for the embryos were obtained after soaking
the seeds in water for a day.
The water-contents indicated by the loss of weight of the berries when air-dried are
taken from the table at the end of Chapter XII. The entry for April 20, 1909, relates
to an observation made on fruits in the same stage in the following year.
The diminution in the weight of the fruit in February and March is due to most of
the larger fruits having fallen.
THE REST-PERIOD OF SEEDS
429
FIGURES ILLUSTRATING THE GROWTH ON THE PLANT OF THE SEED
AND EMBRYO OF THE Ivy (HEDERA HELIX) FROM NOVEMBER
1908 TO JUNE 1909.
November 9.
Seed, 4 '5 mm.
Embryo, 07 ,,
December 3.
Seed, 5 '5 mm.
Embryo, i'6 ,,
January 9
Seed, 6 mm.
Embryo, z 'z mm.
January 24.
Seed, 7 mm.
Embryo, 275 mm.
February 21.
Seed, 67 mm.
Embryo, 2*5 ,,
March 19.
Seed, 6 '3 mm.
Embryo, 2*3 ,,
April 20.
May 1 6.
Early in June.
Seed, 6*3 mm.
Embryo, 4 mm.
Seed, 6 mm.
Embryo, 6 ,,
Germinating seeds.
All enlarged ; in the case of the seeds twice the natural length, and in the case of the
separate embryos four times, but the germinating seeds are drawn about one and a half
times the normal length.
With the exception of the germinating seeds, therefore, all the seeds are drawn to
one scale, and since the separate embryos are also drawn to one scale, it follows that the
changes in size are respectively in true proportion.
These figures are intended to illustrate the results given in the preceding table.
430 STUDIES IN SEEDS AND FRUITS
size being principally due to the growth of the endosperm.
The small embryos also added to their bulk, but at a rate not
much faster than the seed. They displayed but little evidence
of having grown at the expense of the food-reserve, and
remained white, with their cotyledons appressed. From the
end of January up to the middle of March there was a sus-
pension of the growth of the fruit, seed, and embryo ; and
here the observations for that season ended, the embryo
remaining in the same colourless, inert condition. The winter
was severe, and I think it very probable that under milder
conditions there would not have been this check.
The latter part of the history of the growth of the embryo
in the seed on the plant is supplied by my own observations
during four successive springs. Since their general results
agree, I have only given in the table those for 1909 and 1910.
It is there indicated that after March the embryo grows with
arc ' fair rapidity. Taking all the data of the four years, the average
growth in the spring would be as follows : By the end of
March or the beginning of April the embryo would be about
3 millimetres long, or just half the length of the kernel, but
remaining white and showing no enlargement of the cotyledons.
During the latter part of April and the early part of May most
of the berries fall to the ground, their detachment being
hastened by wind and rain. The seeds of those that remain
usually display embryos 4 or 5 millimetres long, increasing
perceptibly at the expense of the albumen and with enlarged
green cotyledons. As May advances the embryos attain the
length of the kernel (6 to 7 millimetres), some of them
becoming even longer, so that they are compelled to accommo-
date themselves to the kernel's length by bending, as shown
in the figure for May 16. A few seeds will be found
germinating within the fruit, which has already begun to
shrivel and soon drops off. Whilst the berry is attached to
the plant the radicle pierces the seed-coats, but not the pericarp,
the hypocotyl becoming bent over the seed inside the fruit. In
these germinating seeds the albumen has largely disappeared.
THE REST-PERIOD OF SEEDS 431
In different years, when the season is unusually mild, all
the stages above referred to the month of May will be found
in April. The seeds will not generally be found all germinat-
ing in the same berry, but all will show embryos advanced
in growth. Nature only offers a small number of fruits to
illustrate the germination of the seeds on the plant, since the
final stage is usually anticipated by the early shrivelling and
detachment of the berry when the embryo is 3 or 4 millimetres
long, the result of late frosts, wind, and rain. However, of
the surviving berries the proportion with germinating seeds
in May will vary from 10 to 50 per cent. By the beginning
of June all the fruits have fallen. I have here been describing
the behaviour of Ivy berries in the mild climate of South
Devon. The growth of the embryo in the spring is a
good deal influenced by the situation of the plant. Thus in
sunny places sheltered from the cold winds it will be much
in advance of that found in plants growing in bleak, exposed
localities.
The nature of the growth of the embryo of the Ivy during TWO modes
the winter is well brought out in the table. The seed grows the^emliryo 01
with the berry and the embryo grows with the seed, the , f the l jy m
i i 11 i 1-1 the seed on
increase in its proportional bulk being but slight. There is the plant.
little or no growth at the expense of the endosperm, the
embryo remaining white and the cotyledons retaining their
small dimensions. But with spring in progress the berry and
the seed no longer add to their size. The embryo, now 4
or 5 millimetres long, grows independently. Its cotyledons
enlarge and its whole surface becomes green, this independent
growth being associated with a gradual diminution of the
food-reserve, so that when the seed is found germinating in
the berry on the plant, the albumen has mostly disappeared.
The two kinds of growth of the embryo, first during the
winter with the seed and the fruit, and then in the spring at
the expense of the albumen, are the conspicuous features in
the vivipary of the seeds of the Ivy. We can thus distinguish
two stages in the after-ripening of these seeds.
The con-
nection
between the
late flower-
ing and the
viviparous
tendency of
the Ivy.
The
tendency to
vivipary
displayed by
acorns.
43 2
There are therefore two singular features that must be
closely linked together in the life-history of the Ivy the
autumnal flowering and the ripening of the seeds on the
plant during the winter, followed by germination in the spring,
without the intervention of a rest-period of more than a few
weeks' duration. Much depends on the causal connection
between them. If the plant is viviparous because it flowers
in the autumn, then the vivipary appears to be adaptive ; but
if it flowers late because it is viviparous, then the autumnal
flowering would be an adaptation. It may be that the cause
of the late flowering is to be found in the absence of any
proper rest-period for the seed. For if the plant flowered in
the spring, it would mature its fruit at the close of the summer,
and the seedlings would be cut ofF by the winter's cold. The
retention of the viviparous habit would lead to extinction,
unless flowering occurred in the autumn. It is likely that a
difference in the mode of ripening of the seeds may explain
why Hedera Helix (as stated by Kerner) grows in Central
Europe without any protection from the winter's cold, whilst
the Ivy of Southern Europe (Hedera poetarum), which is very
similar in characters, can only survive the winters of Central
Europe under a protecting roof.
I come now to my observations on the normal tendency
to vivipary displayed by the seeds of acorns (Quercus Robur).
This is not only exhibited in the occasional germination of
these fruits on the tree, but in the actual stages of growth of
the seed within its shell before maturity is reached. The steady
growth of the seed on the tree long after the pericarp or shell
has begun to dry has been discussed at length in Chapter XIV.
It was then said that the tendency of a seed to continue its growth
on the plant after the pericarp or fruit-case has commenced to
dry and lose weight, finds its final expression in the germination
of the seed on the plant, or, in other words, in vivipary. Such
was the tendency displayed by the oaks near Salcombe, in South
Devon, during the successive autumns of 1908 to 1911 ; and
doubtless it is characteristic of this tree in other localities.
THE REST-PERIOD OF SEEDS 433
It can be easily demonstrated that ripe moist acorns are
able to proceed at once with germination if placed under
conditions inhibiting the drying of the fruit. Thus on
September 17, 1908, I collected some ripe acorns and placed
them at once in damp moss in a warm cupboard. They were
still biologically connected with the cupules, and their shells,
though beginning to brown, were still thick and moist.
Within eight days I found some of them germinating normally,
and one of them when planted grew healthily under protection
during the winter. (Whilst preparing this chapter (September
1911) 1 repeated this experiment with green ripe acorns show-
ing no signs of drying, and possessing, as in the first case, entire
shells. In five days half of them were splitting their shells,
and several of these were protruding the radicle.)
Every autumn I noticed a small but variable number of
ripe acorns showing signs of germination on the trees in the
splitting of their shells and in the slight protrusion of the
radicle. The growing seed had burst the fruit-case, and in
many cases it was evident that the seed was larger than its
shell. This was recorded at the end of September 1908, in
the first half of October 1909, in the middle of October 1910,
and in the second week of September 1911. A number of
the split nuts placed at once in wet moss in two different
autumns were found in four or five days well advanced in the
germinating process. When the acorn begins to split at its
sides it is full-sized, moist, and green, and is still vitally con-
nected with the cupule. Usually the protrusion of the radicle
is not great on the tree ; but I can recall a case where its
growth was considerable, and where the inner surfaces of the
cotyledons were turning green whilst the fruit was still
attached.
This attempt at germination on the tree soon brings about The fate of
the fall of the nut. The shell browns rapidly as it dries, and t h at g er min-
the fruit is soon vitally disconnected from the cupule. Generally **ee n ^
the fallen acorn dies ; but it must frequently happen in moist
mild weather that it continues the growth commenced on the
28
434 STUDIES IN SEEDS AND FRUITS
tree ; and if it is subsequently protected by the fallen leaves,
there is no reason why it should not survive an ordinary
winter's weather and be ready for active growth in the spring.
Here is an experience that bears directly on this point.
Some acorns which had germinated a few days after being
picked from the tree in October were left covered up in the
basin of wet moss in my greenhouse and forgotten. Early
in March I was surprised to find that several of the acorns
were still alive, with radicles protruding about an inch, the moss
being still damp. The winter growth had been very slight,
the germinating seeds having undergone a period of almost
complete repose. Healthy seedlings were raised from them.
During the months of January and February there had been
no artificial heat in the greenhouse, and the contents were at
times frost-bound, the lowest reading of the thermometer
inside the house having been 23 F.
The proportion of acorns exhibiting the early stage of
The pro- germination on the tree in the autumn varied in different years.
acornTthat Thus in the season of 1909 I placed it at 2 per cent. In
begin to ion after the abnormally long and dry summer, extending
germinate on ~ ' / <
the tree. into the fall of the year, the proportion in the fourth week
of September was as high as 10 per cent. The exceptionally
dry season had not affected the foliage of the trees, whilst the
fruits were much larger and much more abundant than in the
previous years. Whilst in 1908 the average weight of an
acorn was from 60 to 70 grains, and in 1910 from 50
to 60, in 1911 it was about 100 grains. The fruits
ripened nearly a month earlier than usual, being mature in
the middle of September instead of early in October.
I had a remarkable experience with ripe acorns during
Thegermin- three successive Octobers. After being gathered from the
ation of . . . r . , . . ,
detached tree in the green moist stage, berore any loss or weight by
during the drying had occurred, I placed them on each occasion in a
drying fay saucer in a room which was rather damp, as there was
process. *
no artificial heat. The nuts were quite entire and showed
no signs of splitting their shells. On the first occasion
THE REST-PERIOD OF SEEDS 435
eleven out of fifty-five nuts were found in the typical
germinating state about seventeen days after. The fruits
had germinated whilst actually drying ; and I estimated their
loss of weight when germination began at from 10 to 20
per cent., the total loss of weight of a mature fruit when
completely air-dried being from 50 to 60 per cent. The
same thing happened under the same circumstances in the
two following Octobers. In an experiment carried out whilst
writing this chapter, I placed thirteen ripe acorns in a dry cup.
In nine days one was protruding its radicle and two were
splitting their shells, the aggregate loss of weight since the
seeds were gathered in the moist entire condition from the
tree being just 10 per cent.
We are not concerned here with after-ripening, such as
frequently occurs with detached albuminous seeds, since in
the mature acorn on the tree the embryo is fully formed
and develops a plumule which may be turning green. The
interest lies in the fact that germination took place in the
case of a mature exalbuminous seed in a drying fruit. It
is evident that with the acorn the ripe moist seed is not
necessarily prevented from proceeding continuously with its
growth by drying in air for a week or two. But the drying
process must be slow. In most cases the loss of water is too
rapid and the tendency to proceed at once to germinate is
suppressed. Evidently the detached ripe acorn, provided that
the drying is checked, can make good use of the water it
holds, which is more than is actually needed for the continued
growth and germination of its seed. Anything that impedes
the air-drying process of the freshly detached acorn will assist
the seed in its endeavour to dispense with the rest-period
altogether.
In this way we may explain Uloth's observation of acorns
germinating in ice. The explanation given in Nobbe's book Uloth's
(p. 104) is, that the requisite water would be supplied by the f acorns n
melting of the surrounding ice through the natural warmth germinating
in ice.
of the seed. However, we learn from my observations above
43 6
STUDIES IN SEEDS AND FRUITS
Vivipary in
Artocarpus
incisa.
Crinum.
given that the detached fresh acorn does not need any water
from outside in order to proceed at once with the germinating
process. In fact, we have seen that such acorns will germinate
without a rest-period after losing a good proportion of their
weight by drying. Any check to the drying process of the
fresh detached nut would directly aid the seed in proceeding
continuously with its growth and in dispensing with the usual
period of repose. This check would be found in the inclusion
of acorns in ice. Drying would thus be inhibited, and the
acorn would have sufficient free water within its own substance
for the uninterrupted growth of the seed.
For important particulars relating to the stages of growth
of the acorn the reader is referred to two tables given on
PP- 303, 3 11 -
Germination within the fruit on the tree may take place
in the case of the seeded variety of the Bread Fruit (Artocarpus
incisa). This came under my notice in Grenada and Tobago.
Mr Anstead, the Superintendent of the Botanic Gardens in
Grenada, assured me that this habit was well known in the
island. In the case of a fruit that had just fallen I found a
third of the seeds (about sixty in all) germinating or " showing
eyes," as the coloured people call it. In another fruit that
had fallen the day before three-fourths of the seeds were
germinating. It was evident that germination began on the
tree in the ripe fruit ready to fall. With the ordinary seedless
variety suckers burst through the ground all around the tree.
They are absent altogether with the seeded kind.
I made some observations on the viviparous habit of
detached Crinum seeds. This habit is well known, so that I
will refer the reader to Note 29 of the Appendix for my
remarks on the subject. Here, in the case of seeds packed
away in my collections, germination took place in seeds that
had lost more than half of their weight, the embryo increasing
its size ten- or fifteen-fold within the seed during the drying
process.
THE REST-PERIOD OF SEEDS 437
Some of the works quoted in this chapter are Goebel's
Organography of Plants ; Kerner's Natural History of Plants ;
Ewart's "Longevity of Seeds" (Proc. Roy. Soc. Victoria, 1908) ;
Ewart in Trans. Biol. Soc. Liverpool, 1896 ; Nobbe's Handbuch
der Samenkunde ; Schroder in Untersuch aus dem Botan. Inst. zu
Tubingen, Band ii., 1886.
SUMMARY
(1) The rest-period represents a break in the continuity of the
young plant's life, and is the eftect of external conditions acting
through the parent and the fruit on the seed. The author's main
object in this chapter is to establish the inherent capacity of all
embryos to proceed uninterruptedly with their growth, whatever their
stage of development when the resting state is imposed.
(2) In dealing with this subject he discusses the prevalence of the
resting state in seeds, and the well-known circumstance just implied
that the rest-period has been imposed on seeds in all stages of develop-
ment of the embryo.
(3) In the first case, he shows that this state of repose is often very
transient with a large number of plants, and that when we reflect
that many plants experience " after-ripening " in their seeds, when the
embryo continues to grow after the seed has entered the resting state,
the rest-period is deprived of some of its prominence as a feature in
plant-life (p. 418).
(4) As concerning the second point, he directs attention to the
great importance of Goebel's observations on Anemone and Utricularia,
from which we learn that all the stages, from that of the unsegmented
acotyledonous embryo to that of the embryo producing its cotyledons
and even its first leaves, may be found not only in the resting seeds of
different individuals of the same species, but even in the same individual.
It is suggested that the problem thus confined within such narrow
limits presents an inviting field for further inquiry (p. 420).
(5) The author points out that the inherent ability of the embryo
to continue its growth without the interruption of the rest-period is
itself implied in its existence in such varied stages of development in
the resting seed. The familiar after-ripening of seeds, above noticed,
and the well-known occasional germination on the plant of seeds
accustomed to submit to a normal rest-period, are also facts indicative
of this inherent capacity (p. 420).
(6) Experimental proof is adduced to show that in the case of any
plant taken at random, such as Arenaria, Iris, Vicia^ Quercus, etc., it is
438 STUDIES IN SEEDS AND FRUITS
possible, by placing under suitable conditions the soft uncontracted seed
of the moist living fruit, to induce it to proceed continuously with its
growth and to germinate without any resting stage (p. 421).
(7) Coming to the question of causation, it is urged that we must
distinguish between the general causes of the rest-period and t'le
special influences that determine the stage of development of the
embryo at which the period of suspended growth is imposed (p. 422).
(8) In references to the general causes it is shown that although
in some ways certain climatic influences may be recognised, as those
concerned with excessive humidity, yet the subject is really far more
complicated than such an explanation would suggest. Indeed, the
causes must be sought far back in the plant's life history, not ir the
seed alone, but in the seed as it depends on the fruit, and in the fruit
in its dependence on the mother plant, and in the mother plant in its
responses to its conditions of existence (p. 422).
(9) Being unprepared to undertake such a profound inquiry, the
author here limits himself to the influence of the fruit, and that only in
an illustrative way. He shows that the suspension of the active growth
of the seed presents itself as the result of failure in the co-ordination or
co-operation of the growth of the seed and the fruit. Only ii the
truly viviparous plant, as in Rhizophora-^ is there complete co-ordination.
Over both seed and fruit hangs the fate of ultimate detachment from
the parent ; but this fate may be avoided if the two co-operate, so that
when the fruit is ripe the seed has already begun to germinate (p. 423).
(10) Taking the capsule and the legume, it is remarked that there
is a lack of co-ordination in the first because the seeds are exposed in
the moist fruit before the embryos can lead an independent existence ;
and there is a lack of co-operation in the legume because the pod begins
to dry before the seeds can sprout. There is not much significance in
the mere statement that dehiscence takes place early in the capsule and
late in the legume. But there is a good deal of meaning when,
regarding the possibilities of vivipary, we state that dehiscence occurs
too early in the capsule and too late in the legume. Nature has
wrongly timed the opening of the fruit in both cases (p. 423).
(u) As showing the way in which the rest-period may be imposed,
and how the life of a young plant well able to proceed with its growth
may be abruptly suspended, the case of the seeds in the woody legume
of Poinciana regia is taken (p. 425).
(12) With regard to the special influences that determine the stage
of development of the embryo at which the rest-period is imposed, the
author looks for them in the different stages of growth of the fruit and
the seed. Since, however, the rest-period is directly determined by
the limit of the fruit's growth, and since the limit of the fruit's growth
is determined by the mother plant, it follows that the mother plant has
THE REST-PERIOD OF SEEDS 439
the first word to say in shifting the plane of the rest-period. But re-
stricting his remarks to the special influences of the fruit, the author
points out that the more the fruit's growth is in advance of that of the
embryo, the earlier should be the onset of the rest-period, and that only
when the two are co-ordinated does true vivipary occur (p. 425).
(13) Then follow the results of the writer's observations on the
viviparous tendency displayed by the seeds of the Ivy (Hedera Helix\
and of the Oak (Quercus Robur). In the case of the Ivy it was
ascertained that the ripening of the seed on the pknt during the
winter is followed by germination in the spring without the inter-
vention of a rest-period of any long duration. The ripening in the
winter months is characterised by the associated growth of berry, seed,
and embryo, the embryo growing as the endosperm increases. The
ripening in the spring is confined only to the embryo, which grows at
the expense of the endosperm. The result is germination on the
plant in the case of the seeds of berries that remain long attached to
the parent (p. 427).
(14) In the case of the Oak it is established not only that the
freshly detached moist acorns can be readily induced to pass on to
germination, but that there is a decided tendency for the ripe acorn on
the tree to dispense with the rest-period. This viviparous habit has
been already regarded as the final expression of the tendency of a seed
to continue its growth on the plant after the fruit-case has commenced
to dry, a capacity that was established for the seed of the acorn in
Chapter XIV. As a result the seed not infrequently becomes too
large for the fruit-case and splits the shell, the radicle protruding when
the acorn remains some time longer on the tree. The proportion
of acorns beginning to germinate on the tree varied between 2 and
10 per cent. (p. 432).
(15) The chapter is concluded with some notes on the germination
of the seeds of Artocarpus incisa (seeded variety of the Bread-fruit tree)
in the fruit on the tree, and on the continuous growth of the embryo
of Crinum during the drying of the seed (p. 436).
CHAPTER XX
Intro-
ductory.
The seed is
less special-
ised and less
conditioned
than the
plant.
THE COSMIC ADAPTATION OF THE SEED
THE physics of seeds ought to be a subject of deep interest, if
only from the circumstance that whilst the seeds, generally
speaking, can live or retain their vitality in any climate, the
parent plant is as a rule rigidly restricted in this respect. The
fact that the seed is less specialised for terrestrial conditions
than the parent plant is one of the first suggestions that nature
offers to us when we approach the consideration of seeds from
the cosmic standpoint. It is one of the purposes of this
chapter to extend this distinction by showing that seeds might
live on a planet where conditions destructive for the parent
plant prevail. Where the discussion appears disconnected and
inconsistent, the defect is usually due to the circumstance that
I have here strung together notes and ideas jotted down
generally during botanical rambles in the last four years. To
endeavour to adjust some of them would be to displace others,
so I have preferred to let them stand, feeling assured that in
the opening up of new ground of this sort the reader will be
to my faults a little blind.
It was the behaviour of the seed of Guilandina bonducella in
the oven and in the balance that first led me into these specula-
tions. The spectacle of a plant-embryo living its own life in
its hermetically sealed case and irresponsive to outside con-
ditions seemed to offer a near approach to an unconditioned
existence on this planet. Though crude and only partly true,
this notion proved to be very suggestive ; and I came to see
440
THE COSMIC ADAPTATION OF THE SEED 441
that the transition from the seed to the full-grown plant is a
transition from the less conditioned to the more conditioned
state of plant-life. The seed often appears to be largely
independent of its conditions on the earth's surface ; but this
could only be true in a relative sense as compared with the
plant. The plant is conditioned only for terrestrial existence,
the seed for existence in the cosmos. This it is that makes
the seed so often seem to be out of touch with terrestrial
conditions. Whilst there is so much about the seed and
its fate that appears to be haphazard and to be determined
by accidents when regarded from the standpoint of our
planet, it may be, as before observed, that regarded from
the broader standpoint of the cosmos such a lack of harmony
does not exist.
The seed in the universe or cosmos may be like a great
traveller on the earth adapted to all climes and acquainted with
all peoples. He is cosmopolitan in his habits, and as such
seems fitted for all conditions. Yet if we were to ask the
peoples of the different countries amongst whom he had lived,
we should find that they judged him merely from the restricted
standpoint of their experience, and that only in proportion as
he acquired proficiency in their special way of living would
he be regarded as a profitable member of their society. His
general fitness would not be appreciated by a North American
Indian if he could not follow a trail, or by a Pacific islander if,
when stranded on a coco-nut islet, he could not climb the tree.
Though in a general sense fitted to live everywhere, in a special
sense he would be suited for nowhere. Yet the judgment of
the savage would be the pity born of ignorance.
So it is with ourselves and the seed. We only notice its itspotenti-
want of special fitness for its terrestrial life. Whether it will sent^with
reach a suitable soil or whether it will ever germinate at all S/* 1 *"^
hfe-condi-
seem to be matters of chance. Yet we are apt to forget that tions that
r ..... . . extends
its great capacity tor preserving its vitality presents us with a beyond the
range of conditions that extends beyond the earth. A seed earth>
that could withstand the intense cold of space, or is able to ger-
442 STUDIES IN SEEDS AND FRUITS
minate after prolonged immersion in an atmosphere of nitrogen
or chlorine or in alcohol, would lack those special adaptations
to terrestrial life which give the appearance of fitness to the
typical organism. The variations of climate on our planet
merely concern the purely terrestrial characters of plants. The
seed often ignores them. Theoretically a seed should live for
ever ; but unceasingly subjected on the earth to the strain of
special conditions, its tenacious hold on life in any circumstances
is apt to be lessened, so that with us it evinces only the
tendency to immortality. It cannot be doubted, indeed, if
this point of view be correct, that seeds have in varying degree
undergone adaptations on the earth, and that a greater fitness
for the special terrestrial conditions has often become a source
of weakness in an organism generally adapted for existence in
the cosmos.
Offers a clue In spite, however, of the disposition to yield to the adaptive
tions of influences of terrestrial conditions, the seed still offers us the
on ty instance of a terrestrial organism that is non-terrestrial
in many of its potentialities. It seems to be the only clue
presented to us on our planet to the conditions of existence
in another world, a world such as the moon appears to be,
where the requisite conditions for plant-development beyond
the seed-stage, such as we know them, do not probably exist.
If we study the ways of the seed we may be able to learn
something of the nature of existence possible on the lunar
surface ; and it is quite feasible that vegetable organisms in
what we term the seed-stage of their existence may be living
on the arid surface of that satellite, propagating themselves
perhaps by some means unknown to us.
Although most of what is written above may be mere
fancy, it is a fancy that might stimulate investigation ; and it
should be remembered in this connection that the transference
of germs from one world to another is on this view far from
preposterous. De Maillet, when he promulgated this notion
about two centuries ago, made a wild guess ; but modern
investigators have independently advanced the same idea. In
THE COSMIC ADAPTATION OF THE SEED 443
concluding these introductory remarks to this chapter, I would
point out that we on this planet, with our limited experience
of conditions of existence, are not in a position to judge of
" misfits " in nature. Beyond us lies the cosmos, of which the
earth forms a part, and that an insignificant one ; and we
should surely be more liberal in judging nature when lack of
harmony occurs if we were to regard it in this light only as
connected with our planet. What is a disharmony on earth
may be in tune with the life of the cosmos. For the naturalist
the " great beyond " is an unexplored region. Yet it may
prove to be full of suggestiveness in matters terrestrial. The
life of one world may be the complement of another ; and
both worlds may be largely unintelligible when viewed alone.
Let us hope that in time enlightenment will come.
In this chapter I propose, therefore, to avail myself of the
privilege of giving freer play to the fancy than a strict
adherence to the ordinary canons of scientific research usually
allows. This licence I venture to claim as a recompense for
the tedious labour involved in the elaboration of the abundant
" facts and figures " in the preceding chapters. When dealing
with the rest-period, one of the most mysterious features in
the history of the seed, I treated the subject on orthodox lines.
Here it is my intention to break through the bounds that
there held me in check.
In pursuing such speculations as those concerned with the The signifi-
significance of the seed, one finds oneself in difficulties at the see( j.
outset, not only on account of the number of roads approach-
ing the subject, but also because it is by no means easy to
appreciate their relative value. Those starting-points that
present us with the largest view of the matter will probably
be the safest for a first selection ; and, this being granted,
we have to choose whether we will deal with the conditions
of plant-life in which the seed-stage is involved or with the
general biological phenomena of the seeds themselves.
One consideration has determined my choice, and it is
444
STUDIES IN SEEDS AND FRUITS
Adaptation
of the seed
for existence
in other
worlds and
of the plant
for terrestrial
life only.
The differ-
ence between
the cosmic
conditions
and those
specially
terrestrial.
this. We get a tangible clue at the very start when we
reflect that in its habits the seed is in a cosmic sense more
cosmic than the fully developed plant. The plant needs an
atmosphere, whilst the seed does not. While the plant appears
to be specially adapted for terrestrial conditions, the seed might
conceivably retain its vitality where no atmosphere of the
terrestrial type exists. Admittedly it can withstand the cold
of space, and it might survive even the extreme conditions
of the lunar surface. Thus, whilst the seed is adapted as
such for existence " in other worlds than ours," the full-grown
plant seems to be fitted for terrestrial life only. The question
of " cosmic adaptation " as a general principle is discussed in
a later page of this chapter. Here, then, I take the position
that whilst the seed is cosmically adaptive, the plant as far as
we can know at present is only terrestrial in its adaptation.
It will probably prove, however, as will subsequently be shown,
that every stage in the development of the plant-organism has
its cosmic side, but that the cosmic element diminishes as
the organism develops, being greatest in the seed and least
in the full-grown plant.
The cosmic conditions would be those common to all the
planetary worlds ; whilst the terrestrial conditions would be
those peculiar to our planet. Now, the nature of the difference
between the cosmic conditions common to all inhabited worlds
and the special conditions of any particular planet is the first
question that presents itself. How should we characterise it ?
It would be fallacious to assert that the continued existence
of a seed during a voyage in space or on the surface of a
planet without an atmosphere like that of the earth would
imply existence under a negation of conditions. It would
not even involve a complete negation of terrestrial conditions,
since the terrestrial conditions would comprise a residuum
which our planet possesses in common with all the planetary
worlds. These residual conditions are common to the cosmos,
and we may here include space itself. They are the cosmic
conditions to which the seed is adapted.
THE COSMIC ADAPTATION OF THE SEED 445
Now what is the nature of the difference between the Appeal to
cosmic conditions and the specially terrestrial conditions ? influences of
On our planet we can recognise by their effects two kinds of
influences those which result merely in the increase or in
the diminution in the size of the plant-organism, and those
which bring about changes in the characters of its type. As
examples of the first effect we may associate the gigantic
Sequoias of California with the dwarfed pines of Japan ;
whilst to illustrate the second we may cite the ordinary
variation of plants under different environments. In the
first we see the effect of expansion and contraction of the
life-conditions. In the second we have the result of their
diversification. When nature diversifies the conditions, only
a part of the organism responds to each change in the environ-
ment. When nature relaxes their pressure or increases their
rigour the whole organism responds ; and it is evidently to
this order of things that we must refer the differences in
effect between the cosmic and the special planetary conditions.
Take the indications afforded in the culture of dwarf trees, The dwarf-
where man so successfully imitates the repressive side of nature. e "f j n rees '
In an article on " The Dwarf Tree Culture of Japan " by Mr Jjf u t ^ ation
Percy Collins that was published in the Windsor Magazine repressive
for October 1907, we find the method thus pithily described : nature.
" Everything is done to concentrate the life of the tree within
the narrowest possible limits. And at last, after years of un-
remitting labour, the tree begins to respond to the touch of
its master. It loses its tendency to shoot forth lusty and far-
reaching twigs. Its leaves become tiny and proportioned to
its dwarfed branches. It surrenders in the fight for liberty
and becomes quiet and tractable." Many kinds of forest trees
ultimately yield to this repressive treatment, a period of at
least half a century being required for the production of a
good saleable dwarf tree. Of course with herbaceous plants
much less time is needed. The writer of this book about
twenty years ago conducted a series of experiments on the
effects of very dry conditions on the growth of Bidens cernua
In this way
it is conceiv-
able that the
growth of a
plant could
be confined
to the
cotyledonary
stage illus-
trated by
Wel-
witschia
and even to
the stage of
the resting
seed.
The seed
would thus
represent the
cosmic life of
the plant and
the full-
grown
organism its
special
terrestrial
form.
446 STUDIES IN SEEDS AND FRUITS
and Bidens tripartite two species that grow in wet stations by
the sides of ditches, ponds, and rivers. After three generations
the height of the plants was reduced from 17 or 18 inches to
5 or 6 inches, the fleshy stems becoming dry, woody, and wiry,
the length of the achenes being reduced by half. The details
of this experiment are given in Note 13 of the Appendix.
What man effects after years of tedious labour in the
dwarfing of trees, nature accomplishes in the course of ages
through the rigid pressure of the life-conditions. It is even
conceivable that in time, by a still more severe treatment of
repression, man could accomplish what nature seems to have
aimed at in the case of the West African Welwitschia. In
other words, he would be able to confine the growth of the
plant to its cotyledonary stage. It is arguable, indeed, that he
could carry this treatment so far as to destroy the possibility of
a special terrestrial existence, or, to put it in ordinary language,
he would restrict the life of the plant to the seed-stage. The
seed would be by no means devitalised ; but the conditions on
which the maintenance of its vitality depended would be only
those which the earth possesses in common with the cosmos.
For the experimenter the seed would merely be a plant-
organism that could not proceed with its development on
account of the repressive influence of the conditions. Sub-
stitute nature for the experimenter, and we should regard the
seed as representing the organism's response to the iron-bound
cosmic conditions, whilst the subsequent stages of growth would
depend on the relaxation of the pressure of these conditions on
the earth's surface. The seed would thus represent the cosmic
life of the plant-organism, whilst the fully developed plant
would be regarded as its special terrestrial form ; and we might
almost hold that the flowering and seeding stage represents the
plant's effort to return to its general cosmic habit, the vegeta-
tive mode of reproduction being viewed as based on purely
terrestrial necessities. Under conditions where the pressure
of the life-conditions is much less than prevails on our planet
it is conceivable that the whole plant would be " proliferous."
THE COSMIC ADAPTATION OF THE SEED 447
We have above been concerned with the effects of the
repressive influence of the life-conditions. I will now illustrate
the results of their relaxation or expansion. Here the con-
dititions press gently on the organism, and we see the results
in the giants amongst our trees, as represented by the Sequoias The
of the elevated plateaus and flat-topped mountain-spurs of the illustrate the
Sierra Nevada in California and by the gigantic Eucalyptus e .xpansive
trees of the deep valleys and gorges of the mountains of nature.
South-eastern Australia.
Those who have read Clarence King's Mountaineering in
the Sierra Nevada and can recall his graphic description of the
environment of the Sequoias will remember that it was the
peculiarity in the climatic conditions that appealed to the imagina-
tion of this gifted writer. Life's conditions press lightly on the
trees of this ancient race. "Possessing hardly any roots, and
resting on the ground with a few short pedestal-like feet penetrat-
ing the earth for a little way," they grow under " a sky which
at this elevation of 6000 feet is deep, pure blue, and often
cloudless." ..." It is, then, the vast respiring power, the
atmosphere, the bland regular climate, which give such long
life, and not any richness or abundance of food received from
the soil." So it may be premised that in a kindred fashion
nature makes existence easy for the giant Eucalyptus trees
that attain heights of 400 feet and over in the shelter of the
deep valleys and gorges of the mountains of Victoria, as
described by Thomas Ward in his Rambles of an Australian
Naturalist (1907).
From the point of view, therefore, of plant-life which Postulating
postulates a flora of the cosmos, the stage of development cosmos, the
attained depends on the pressure of the conditions, being
least advanced where the conditions are the most rigid and of the same
11- -i i 11 r i i r type in
unyielding, as in the state where only the stage or plant-lire different
represented by the seed is possible, and most advanced where depends on
the conditions are light and easy, allowing the relatively un- the degree of
orcssiirc 01
hindered growth of trunk, branch, and foliage. From such a the condi-
standpoint also the flowering and seeding stage would present
Cosmically
viewed, the
laws of
inheritance
may lose
their validity.
STUDIES IN SEEDS AND FRUITS
itself as the result of an increase in the repressive influence of
the conditions, or, in other words, as above suggested, it would
indicate a tendency to return to the primitive cosmic state as
presented in the seed. There is a profound significance in the
notion of the gardener that if he gives a plant " a bad time "
it is more likely to flower and mature its seed. From plants
which have received exceptionally favourable treatment, or, in
other words, plants with their existence specially favoured at
his hands, he would look for " size," an increased tendency to
vegetative reproduction, and but little seed. (See Note 30 of
the Appendix.)
It will thus be seen that we are here concerned with the
expansion of the life-conditions and not with their diversifica-
tion. The seed on this view may represent the minimum of
life's possibilities under extremely contracted conditions of
existence ; whilst the fully developed plant, as we know it,
points in the direction of the maximum growth of the organism.
The seed indicates the cosmic side of the conditions of plant-life
in all the planets ; and it would follow that the same seed
exposed to expanding life-conditions very different in their
character would develop in very different fashions. It is
probable that under conditions far more expanded than those
familiar to ourselves plant development would follow lines
strange and inconceivable to us, conditions capable of extension
in a multitude of ways, and favouring the production of plant-
forms utterly different from any with which we are acquainted,
though recognisable for us in the seeds.
I am inclined to consider that the laws of heredity as we
formulate them on this planet may become very shadowy when
applied to the life of the cosmos, and that with a knowledge
of the life of other worlds we would attach far more importance
to the determining influence of conditions. What we call the
working of the laws of heredity here may be the only response
that the organism could possibly make to terrestrial conditions.
This response, as viewed from the broad field of the cosmos,
we would regard as determined by the conditions of existence ;
THE COSMIC ADAPTATION OF THE SEED 449
whilst, considered from the contracted standpoint of a single
planet, we interpret it as the result of heredity. The laws of
heredity as we frame them on our planet may be real enough
for us, yet they may eventually present themselves as part of
a much wider principle extending over the cosmos. The fact
that an organism must be true to its conditions may indicate
a principle that involves our laws of heredity and very much
more. With this digression I will return to my main
argument.
We are not directly concerned here with any evolutionary
process, but simply with the effect of different degrees of
rigidity of the conditions of existence on the development of
the several stages of a plant's life, from that of the seed to that
of the full-grown organism. Under severe repression a pine
could be forced back into the cotyledonary state in which it
exists in the seed. Under conditions less severe or less
repressive it would develop into the ordinary pine tree ; and
where the conditions pressed lightly on the organism it might
acquire the size of the Sequoias. But we have here neither the
beginning nor the end of the scale of the stages of a plant-
organism, though, as will presently be shown, it is sufficiently
extended to be of some value to us in affording indications of
the line of possible extensions at either the beginning or the
end of the scale in other worlds. Between the two extremes
of indefinite contraction and indefinite expansion seem to lie
the average conditions of our terrestrial plants.
But there is sufficient variation of conditions on our planet Extreme
to enable us to perceive as through dimmed glasses the on the earth
possible influence of extreme conditions in other worlds. For
instance, let us suppose that in very gradual fashion the earth conditions in
,. '.. r ,. /6 . otherworlds.
dries up, losing its water and its atmosphere and presenting
conditions such as now seem to prevail on the lunar surface.
During such changes the plants would be graduallly driven
back to the seed-stage, until, when the earth approached the
lunar condition, all surviving vegetable life would be reduced
to that state. There are seeds, like those of Guilandina bondu-
29
450 STUDIES IN SEEDS AND FRUITS
cella^ that seem fitted to withstand the conditions prevailing on
the surface of the moon. Even now in some of our desert ;
plants we can recognise a stage intermediate between the seed
and the full-grown plant, such, for instance, as in those plants
where, as in the West African Welwitschia^ the cotyledonary
leaves are the only leaves produced by the plant. Cases like
this suggest the penultimate stage of a plant's life in a planet \
attaining the last stage of desiccation. They would also \
represent the first stage in plant-development, when in a
desiccated world inhabited only by plants in the seed-condition
an atmosphere began to form. As the expansion of the con-
ditions of existence proceeded we should obtain a state of '
things similar to that in our own world, and plants would
acquire the vegetative habit familiar to us on the earth. From
this point of view, therefore, the development of the stem and
foliage would be regarded as the plant's response to the pro-
duction of an atmosphere. The return to the cotyledonary
stage would be its response to the gradual disappearance of an ]
atmosphere, until at length it would be forced back to the
seed-stage.
Yet not in this way only could such changes be brought
about. The extension of the possibilities of growth involved
in the expansion of life-conditions may be in other directions.
That indicated by the Sequoias is in one direction, whilst that
illustrated by the gigantic Equisetums and Lycopods of the Coal
Age would be in another. We have already referred to the
case of the Sequoias, where existence is favoured by a bland
regular climate on a mountain-plateau and beneath a cloudless
sky. During the coal epoch the moisture-laden atmosphere
and an ever-clouded sky offered favouring conditions of quite
another type. It was the expansion of the life-conditions in
this direction that gave rise to the huge Calamari<e, Sigi/Iarue,
and Lepidodendra of the Coal Age. It is the contraction of
the life-conditions in the opposite direction that has resulted
in the production of our modern Horsetails (Equisetums} and
Club-mosses (Lycopods]. If our Equisetums have any story to
THE COSMIC ADAPTATION OF THE SEED 451
tell, it is certainly this. Similarly, it is the contraction of the
life-conditions, the waterless, sandy soil, the intense insolation,
etc., that has reduced Welwitschia to little more than a gigantic
embryo. There are seeds, like those of Poinciana regia, as
described in Chapter XIX, where, before the rest-period is
imposed, the embryo, as far as the production of plumular
leaves is concerned, attains a more advanced stage of develop-
ment than we find in the adult Welwitschias.
Although plant-types, for all we know, may be eternal, the The plant is
seed represents the only immutable, or, to put it less forcibly, oT its"cos^nic
the most persistent part of a plant. Excluding its coverings sid * as in its
and appendages, it remains unaltered either under diversified
conditions or in the lapse of the ages. Plants are often thus
connected which have seemingly little else in common. Take,
for instance, the Tillandsias, which vary so greatly in form that
if it were not for the flower and the seed we should probably
never connect them. It is the cosmic characters, the seed with
the preparatory flower, that tend to link plants together. It is
in its cosmic characters that the plant is most persistent and
least mutable.
We possess in our plant-world a scale of possibilities Theter-
ranging from the seeming suspension of life in the resting JnJjJi? * 18
seed to the full development of vegetative life in the tall b j llti t e ? i r )f
forest trees, where, in extreme cases, as in those of Sequoia, the
evenly preserved balance of growth and decay gives promise
almost of eternity. There may be but little difference
between the apparent suspension of life in the seed embryo
and the calm repose of the life forces in Sequoia, where the
organisms seem to be so nicely adjusted to its conditions.
The vital processes, subdued though they be in the tall Sequoia,
may be only proportionately less active than what actually takes
place in the embryo shut up in its hard coverings. Recent
discoveries in physical science would justify us in regarding
the possibility of other means of communication between the
embryo and the outer world than those concerned merely with
respiration, transpiration, and the ordinary nutritive processes
45 2
STUDIES IN SEEDS AND FRUITS
Its indica-
tions of life
in other
worlds.
of a plant-organism. However this may be, there is a promise
almost of eternity in the life both of the seed-embryo and of
the tall Sequoia, though both are ever liable to the accidents of
their surroundings, the seed after its repose of a hundred
years, and the tall conifer after an existence of centuries.
Although we possess a scale of plant-development
beginning with the seed and ending with the fully-grown
plant, yet it by no means follows that our terrestrial scale
presents us with the beginning and the end of the possibilities
of the plant's development, or that we have in the seed the
absolute minimum or in the tall forest tree the absolute
maximum. Yet, looking just beyond the terrestrial scale at
either of its limits, we obtain indications of plant-development
in other worlds. Thus, if at the maximum end of the scale
we emphasise or intensify the life-conditions of the Sequoias on
the Sierra Nevada, so vividly portrayed by Clarence King, we
may be reproducing the conditions under which plants exist in
another planet. Let us similarly extend the terrestrial scale a
little at the minimum end, and it will not be difficult to
imagine a world where vegetable life is only represented by
plant-organisms in the seed-stage or by plants that do not
pass beyond the cotyledonary stage of the West African
Welwitschia.
There is no necessity to suppose that other worlds possess
forms of plant-life altogether outside the terrestrial scale. All
possibilities should be indicated on our sphere. We get there
indications of the possible forms of plant-organisms on a planet
presenting the surface conditions of the moon, where the
conditions for plant-life, as we know it, are reduced to a
minimum for which the seed-stage appears to be alone suitable.
We can also thus obtain indications of the possible forms of
plant-life on planets where the present terrestrial conditions
are greatly extended as regards the denseness of the cloud-
envelope, humidity, and high temperature, where plants like
the huge Calamites of the Coal Age may flourish and where
the rest-period is unknown. Or, again, these conditions of
THE COSMIC ADAPTATION OF THE SEED 453
existence may be expanded in another direction, and we have
then a calm reposeful world with a relatively light atmosphere
but little disturbed by air currents, where the equilibrium
between the organism and its environment is preserved for
almost an eternity and vegetation of the Sequoia type prevails.
We are thus not called upon to suppose that the plant-life
in other worlds is necessarily quite beyond the range of our
terrestrial experience. There are doubtless worlds where the
very conditions of life are on quite another plane, and for such
the indications supplied by the earth would have no value.
But there must be many for which the terrestrial scale would
be ample enough in its scope ; and as our knowledge of these
matters increases it will be along the lines there indicated that
progress will be made. There is, however, much that is not
conceivable in the possibilities of other forms of life under
other conditions ; but the point urged here is that we have not
yet exhausted the conceivable, as suggested by the variety of
the forms of life and of the life-conditions presented on the
surface of the earth.
Before quitting this part of my subject for the discussion of Not the
" cosmic adaptation," let me remind my readers that nothing a'typ^but
in the nature of evolution has been here implied. I have the develop-
ment of
regarded plant-life from this particular standpoint as if the different
doctrine of evolution had never been propounded. Evolu- sanufplant-
tionary phraseology has become so established that it is not
easy to state any problem or to indicate any new standpoint
without doing so in terms of that theory. This seems to be
unfortunate in some respects. In the previous pages I have
been concerned with the development of the several stages of
the same plant-type in response to the varying pressure of the
conditions, the seed-stage and that of the fully developed forest
trees representing respectively the effects of the maximum and
minimum repressive influence as indicated in our terrestrial
scale. (Some further remarks on this matter will be found
in Note 19 of the Appendix.)
All terrestrial organisms are generally adapted to the earth's
Cosmic
adaptation.
Its results
represented
by the
characters
common to
types of
organisms in
different
worlds.
454 STUDIES IN SEEDS AND FRUITS
conditions, and specially adapted to their particular environ-
ment on the planet. Now, we may fairly argue that in their
turn terrestrial organisms possess in common with those of
other worlds an adaptation to the general cosmic conditions
prevailing in those worlds. This cosmic adaptation must be
postulated for all forms of terrestrial life. Though the
primal cosmic habit belongs to all, it is apparent that it may
be concealed or disguised or even lost through changes due
to the special conditions of a particular planet. Thus, regard-
ing the capacity of a seed for resisting desiccation as a part of
its primal habit, the loss of this capacity in the case of the seeds
of certain plants might be viewed as arising from adaptation
to the special terrestrial conditions. Strip an organism of
its specially terrestrial adaptations and the residuum is the
link that joins it to the life of other worlds. The moment
we introduce the life of the cosmos into our speculations
concerning adaptation, we are compelled to make this assump-
tion, since every special adaptation implies a more general
habit of existence. We cannot doubt that the biological
problems of the future will in the main centre round the
disentanglement of this cosmic adaptation, or rather with its
disinterment from beneath the terrestrial adaptations that lie
heaped upon it.
From this point of view an organism is to be regarded as
specially adapted to the earth as a separate world and as
generally adapted to the earth as a part of the cosmos. The
points in common between the types of organisms in different
worlds would thus present themselves as the result of cosmic
adaptation, whilst the points of difference would appear as due
to special adaptations to particular planets. On these grounds
we should expect to find in this world characters that are
not suggestive of any direct relation with the conditions of
existence, or are even out of harmony with them. Man]
difficulties that seem insuperable for us, such as those con-
cerned with reproduction and the distinction between planf
and animals, may ultimately be overcome when regarded from
THE COSMIC ADAPTATION OF THE SEED 455
the standpoint of cosmic adaptation. If the supposition that
the primal cleavage between plants and animals may be cosmic
and not terrestrial goes to account for its inexplicability to us,
may we not imagine that similar difficulties may find their
solution in a like manner ? Even the flowering and seeding
of plants, as before suggested, may be an assertion of the
tendency to resume the cosmic habit. Then, again, man's
endeavours to throw ofF the chains of adaptation that bind
him to the earth or to rise above his conditions may be virtually
the assertion of the cosmic side of his nature. Terrestrially
he may be man, but cosmically he may be of such stufF as
dreams are made of. It is only on the cosmic side that man
could be immortal. In such cases it is likely enough that
our ideas of them are warped and narrowed through regard-
ing them solely from the contracted standpoint of our planet,
and that we have often failed to grasp the true significance of
the problem before us.
Or we may put it in another way. Our senses enable us The cosmic
to follow the later part of the process, which is purely terres- restrUUides
trial, namely, the differentiation and adaptation of types ; but ? f al ? .
' . . ... inquiries,
the earlier portion connected with their origin comes abruptly
into our experience as a completed result affording us no clue
as to the beginning. Stated in a more reverent fashion, the
Creator has permitted us to see the differentiation of a type,
but He has hidden its origin from our view. Of the working
of the larger plan that links the life of this planet to that of
the cosmos we can, as terrestrial beings, have no direct cognis-
ance. Only the operations of its adaptation to life on the
earth are evident to our senses. Viewing our planet as
incomplete in itself, since it is but a fragment of the cosmos,
it follows that in no event can our investigations be ever
complete. There will always be the unfinished border, the Theun-
side that fits with nothing in our experience or system. There border of all
will belong to all inquiries a cosmic side and a terrestrial
side, the one incomplete and indicative of a barrier that
sooner or later brings all investigations to a halt, the other
45 6
STUDIES IN SEEDS AND FRUITS
Cosmic
evolution.
Its control
by the
principle that
the lowest
organisms
possess the
widest
range.
Haeckel on
cosmic
evolution.
neatly rounded off and offering in its adaptive appearance
an easy road for the inquirer.
The principle of cosmic adaptation is implied in all schemes
that postulate a common evolutionary development of
organisms in the cosmos, or what we may term cosmic evolu-
tion, such a scheme, in fact, as Haeckel outlines in The Riddle
of the Universe (English trans., chap. xx.).
Now, with reference to such schemes of cosmic evolution,
meaning thereby the progressive development of higher from
lower forms, it should be at once remarked that although all
organisms would possess the cosmic impress to a greater or
less degree, its extent would vary according to a well-known
principle that is embraced by the evolution theory. Thus,
on our planet the rule prevails that the lower the organism
the wider is its distribution. It would be illogical if we did
not assume that in cosmic evolution the same principle would
prevail. The lowliest organisms, being most widely dis-
tributed in the cosmos, would possess the cosmic impress to a
far greater degree than the higher organisms more or less
specialised in individual planets.
That an evolutionary scheme of the cosmos would be
expected to proceed on similar but much broader lines than in
the case of that limited to our planet is indeed suggested in
Haeckel's book above quoted ; and as the passage bears directly
on this matter, I give it here partly verbatim and partly in
my own words: "We are justified in supposing that
thousands of the planets are in a similar stage of develop-
ment to that of our earth." But although " it is very probable
that a similar biogenetic process to that of our own earth is
taking place on some of the other planets of our system, as on
Mars and Venus, and on many planets of other solar systems,"
by which the lower plants and animals have been evolved,
such as we have on earth, yet " it is very questionable whether
the different stems of the higher plants and animals run
through the same course on other planets as on our earth.
In particular, it is wholly uncertain whether there are verte-
THE COSMIC ADAPTATION OF THE SEED 457
brates on other planets or whether mammals culminating in
man are formed there as on the earth. It is much more
probable that other planets have produced other types of the
higher plants and animals unknown on earth. Perhaps from
some higher stem, superior to the vertebrate, higher beings
far transcending man in intelligence have been formed."
Thus in The Riddle of the Universe do we find the scheme
of cosmic evolution roughly outlined. It involves the
principle established for this planet that the lowest types of
organisms have the widest distribution, from which it follows
that the planets would resemble each other more in the lower
forms and would differ most in the higher forms of life.
Further than this it would be unsafe to go. The How and
the Why of evolution remain still very much in the clouds of
disputation. But, speaking for myself, I do not hold that we
have yet even a glimpse either of its real significance or of the
forces working behind it. The investigations into the nature
and origin of species do not, as I think, aid us at all in the
matter. They may help us to understand the differentiation
of a type, but not its origin, and still less the progressive steps
from lower to higher types. May we not believe that we
see the evolutionary scheme of life only in part on this planet,
that there is an evolution of the cosmos in which the earth with
myriads of other worlds shares, and that much that seems in-
explicable on the earth will find its explanation in other
worlds ?
We know how much light is thrown on one group of The
organisms by studying those related to it, and how much at i
sea we are with an isolated group that is akin to none. May s^eme of 7
we not extend the principle and consider that many of our evolution
difficulties here on the earth will disappear by the extension of a single
our knowledge to worlds outside ? However, from the point P lanet -
of view here adopted any scheme of evolution limited to the
earth must in the nature of things be incomplete. It may
even be that evolution has been misinterpreted by us, and that
the true evolutionist is he who, regarding all types as eternal,
458 STUDIES IN SEEDS AND FRUITS
holds that the gamut of change has been run through unceas-
ingly in endless worlds and that there is nothing ever new,
nothing ever old, all being eternal.
SUMMARY
(1) The author in this chapter gives freer play to the imagination
than is usual with orthodox scientific investigation. In some intro-
ductory remarks he first points out that the seed is less specialised and
less conditioned than the plant, presenting us in its potentialities of
existence with a range of life-conditions that extends beyond the earth.
(2) Discussing first the significance of the seed, he takes the
position that whilst the seed can live in other worlds, that is to say, it
is cosmically adaptive, the full-grown plant is purely terrestrial in its
adaptation.
(3) Then follows a consideration of the nature of the difference
between the cosmic conditions common to all inhabited worlds and
the special conditions of any particular planet.
(4) To elucidate this difference appeal is then made to the different
influences of conditions on our planet, those where the whole plant
responds without alteration of its type, and those where only part of
the plant responds and we get a variation of type.
(5) The changes in the whole plant without alteration of the type
are regarded as illustrated by the behaviour of the gigantic Sequoias of
the Californian Sierra Nevada and of the dwarfed trees of Japan, the
first exemplifying the result of the relaxation of the life-conditions, the
second the result of the increase in their rigour, the one indicating the
expansion of the conditions of existence, the other their contraction.
It is in this direction that we have to look for the influence of the
cosmic conditions.
(6) What man effects after years of tedious labour in the dwarfing
of trees nature accomplishes in the course of ages through the rigid
pressure of the life-conditions ; and in this way it is conceivable that
the growth of the plant could be ultimately confined to the cotyledonary
stage exemplified by Welwitschia^ and even to the earlier stage of the
resting seed.
(7) The seed would thus represent the cosmic side of the plant,
whilst the fully developed plant-organism would be regarded as its
special terrestrial form, the one pointing in the direction of the
minimum of life's possibilities, the other toward the freest conditions
for growth.
(8) Postulating a flora of the cosmos, the stage of development
of the same type in different worlds would depend on the degree
THE COSMIC ADAPTATION OF THE SEED 459
of pressure of the life-conditions, being least advanced where the
conditions are most repressive (and in such cases it might even be
restricted to the seed-stage), and most advanced where the conditions
are light and easy, allowing the relatively unhindered growth of stem
and foliage.
(9) From such a standpoint the flowering and seeding of
terrestrial plants would present themselves as the result of an increase
in the repressive conditions, or of a tendency to return to the cosmic
state ; whilst vegetative reproduction or the proliferous habit would
mark the expansion of the conditions of existence and the fuller
growth of the plant. This goes to explain why in horticulture seeding
is most favoured by harsh treatment and vegetative reproduction and
foliage by generous treatment.
(10) The terrestrial scale of possibilities of plant-life may offer in
its extremes indications of the direction of plant-growth in other
worlds. Under the most repressive conditions, such as prevail on the
lunar surface, plants may be confined to the cotyledonary stage, as in
the case of Welwitschia^ or restricted only to the seed-stage. Where
the conditions are most conducive to growth, the climatic environ-
ment may favour in one planet huge plant-organisms like those of
Catamites^ and in another planet vegetation of the Sequoia habit.
(u) It is on its cosmic side that a plant is most persistent and least
mutable, namely, in the seed-stage. This explains why terrestrial
plants have often little else in common than their seed-characters. It
is on their cosmic side that the primal affinity of plants lies.
(12) The principle of "cosmic adaptation" above assumed is an
extension of the principle adopted as concerning the earth, that all
terrestrial plant-organisms are generally adapted to the earth's conditions,
and specially adapted to their particular environment on that planet.
So, it is argued, a plant-organism may be specially adapted to the earth
as a separate world and generally adapted to the earth as a part of
the cosmos. Strip an organism of its special terrestrial adaptations and
the residuum will be the link connecting it with the life of other worlds.
It is on its cosmic side that a terrestrial organism will usually present
itself as out of harmony with the earth's conditions, and it is on the
cosmic side that all investigations will present an unfinished border,
a side that fits with nothing in our experience or system. The
biological problems of the future will be mainly concerned with the
disinterment of the cosmic adaptation from beneath the terrestrial
adaptations that lie heaped upon it.
(13) Nothing in the sense of the evolutionary theory of the pro-
gressive development of types has been implied in the foregoing discussion,
which is concerned only with the different stages of development of the
same plant-type under the pressure of the life-conditions. But if we
460 STUDIES IN SEEDS AND FRUITS
accept the principle of evolution for the earth, we must necessarily
extend it to the cosmos ; and it is in this connection noteworthy that
the principle of cosmic adaptation must be implied in all schemes of
organic evolution of the cosmos. Thus Haeckel would hold that whilst
the lower forms of plants and animals have probably been evolved on
similar lines on the earth, Venus, Mars, etc., it is questionable whether
the higher plants and animals run through the same course on those
planets. It is thus implied that the principle "the lower the type
the wider its distribution " is true alike of the earth and of the whole
system of which it forms a part. From this it follows that the planets
would resemble each other most in the lower forms of life and would
differ most in the higher forms. Any scheme of evolution applied
only to a single planet must necessarily therefore be incomplete.
APPENDIX
CONTENTS OF THE APPENDIX
PAGE
NOTE i. Swelling capacities of the seeds of Faba vulgaris, Pisum sativum,
Phaseolus vttlgaris, and Phaseolus multiflorus -465
NOTE 2, A. Comparison of the weight of a leguminous seed dried under ordinary
air-conditions after swelling for germination with its original weight in the
resting state ............. 466
NOTE 2, B. A further proof of the mechanical nature of the swelling process of seeds
indicated by their ability to proceed with germination when dried, after they
have absorbed most or all of the water required for germination. (This was
omitted on page 29.) ........... 468
NOTE 3. Comparison of the relative weights of the coats, kernel, and embryo of
resting seeds, and of the same seeds dried after swelling for germination . . 470
NOTE 4. Experiments of Victor Jodin on the " germinative minimum" of Peas
{Pisum sativum} . . 471
NOTE 5 . Canavalia ensiformis and Cana-valia gladiata . . . . . 47 1
NOTE 6. The influence of the coverings on the drying of permeable seeds . . 472
NOTE 7. Mould and impermeability 474
NOTE 8. Dr Gola's tabulated results of his experiments on the permeability to
water of seeds in different degrees of maturity 476
NOTE 9. Classification of the different forms of hygroscopicity by Leo Errera . . 477
NOTE 10, A. On the loss of weight of ripe Gooseberries (Ribes Grossularia) when
dried in air at ordinary temperatures ........ 477
NOTE 10, B. On the loss of weight of ripe berries of the Prickly Pear (Opuntia
Tuna) when dried in air at the ordinary temperature 478
NOTE ii. Table illustrating the history of the fruit of Barringtonia speciosa, begin-
ning with the young fruit and passing through the maturation stages on to the
air-dried detached condition 478
NOTE 12. On the time required by seeds to complete their drying in air, or, in other
words, to acquire a stable weight . . . 479
NOTE 13. Effects of very dry conditions on the growth of Bidens cernua and
Bidens tripartita 480
NOTE 14. Are Bidens cernua and Bidens tripartita distinct species ? . . . 482
NOTE 15. The proportions of pericarp and seeds in the fruit of Theobroma Cacao
(Cocoa) 482
463
464 STUDIES IN SEEDS AND FRUITS
PAGE
NOTE 1 6. The two modes of drying of legumes, as illustrated by Pisum and
Guilandina 483
NOTE 1 7. Comparison of the capsules of Primula verts and of Swietenia Mahogani
as regards the weight-proportion of the placental axis or columella . . . 486
NOTE 1 8. On the colour of embryos ......... 487
NOTE 19. On the retrogression of plants under conditions of stress . . . 487
NOTE 20. [See under Note 28] 488
NOTE 21. Additional results showing the behaviour of different substances after
exposure to a temperature of 100 C 489
NOTE 22. The drying regime of Swietenia Mahogani 489
NOTE 23. The rupturing of the coats of the germinating seed of Entada scandens . 490
NOTE 24. The Hura difficulty 490
NOTE 25. Observations on the weight of resting seeds of Pisum, Phaseolus, Faba,
and Ricinus, showing that the increase in weight during two years recorded by
Van Tieghem and Bonnier is included in the range of the normal hygroscopic
variation 493
NOTE 26. The " replum" of Entada poly stachy a . 494
NOTE 27. The water-contents of the Coco-nut . 494
NOTE 28. Further details supplementing the materials given in the tables on pp.
325-327 and p. 26, for the determination of the drying regimes of fruits and
seeds 494
NOTE 29. On the growth of the embryo in the drying seed of Crinum . . . 504
NOTE 30. The conditions for flowering 506
NOTE 31. Growing Stakes or Live-Fences in Jamaica 507
NOTE 32. Twist Coco-nuts 508
NOTE 33. Table illustrating the method of determining the water and solid con-
stituents in the three conditions of the seed of Entada scandens . . -509
NOTE i (p. 28).
Swelling capacities of the seeds of Faba vulgarly Pisum sativum^
Phaseolus vulgarly and Phaseolus multiflorus.
IN the case of the four plants below named I experimented on
seeds which had also been employed by one or both of the German
investigators, and the comparison of results given in the table is
instructive.
COMPARISON OF RESULTS OBTAINED BY HOFFMANN, NOBBE, AND THE
AUTHOR ON THE SWELLING CAPACITY OF SEEDS OF FABA VULGARIS,
PISUM SATIVUM, PHASEOLUS VULGARIS, AND PHASEOLUS MULTIFLORUS.
Species.
Increase of weight stated as a
percentage of the weight
of the resting seed.
References to pages
in Nobbe's Handbuch
der Samenkunde.
Hoffmann.
Nobbe.
Guppy.
Faba vulgaris .
Pisum sativum .
Phaseolus vulgaris .
104
107 1
... {
'*{
() 96
(d) 7 i
(a) 117
() 101
(a) 90
(6) 101
(a) 91
(b) 137
} 84
\ 109-111, 119
1 II 9 , 122
119, 123, 124
Phaseolus multiflorus
92
98
119 (Weisse Bohnen).
The names of the two varieties of Faba vulgaris and Pisum sativum are given below.
The botanical names are those used by Nobbe in describing his
experiments, except in the case of the last named, for which he gives
Hoffmann's result for " Weisse Bohnen," which is placed with other
species of Thaseolus in the general list of results on p. 119. I have
taken these to be the white-seeded variety of Phaseolus multiflorus^ of
which I experimented on the ordinary mottled seeds.
In the case of Faba vulgaris I experimented on the two varieties
known as Long-pod Beans (a) and Green Windsor Beans (). Whilst
465 30
466 STUDIES IN SEEDS AND FRUITS
my estimates come close to that of Hoffmann, the estimate of Nobbe
is considerably greater, being in excess even of the ordinary weight of
a saturated seed, an increase of 120 per cent, being required for
saturation (see p. 44). Nobbe took as the first indication of germina-
tion the protrusion of the tip of the radicle through the coats ; but it is
shown in the next paragraph that in the case of Peas, when the coats
are much wrinkled, excessive estimates of the swelling capacity may
thus be formed.
Two varieties of Peas were used by me the Early Sunrise Pea (),
a slightly wrinkled kind, and a Marrowfat Pea (/>), with excessively
wrinkled coats. The causes of the great difference in the swelling
capacities of these two varieties, 91 per cent, for the slightly wrinkled
and 137 per cent, for the greatly wrinkled seeds, lie in the excessive
wrinkling of the coats, which not only allows an excess of water to
collect between the kernel and its loosely fitting coats, but also permits
a considerable growth of the radicle before the irregular rupture of the
coats, so that when the seed is weighed it is well advanced in germina-
tion and in a saturated state. This therefore explains not only my
excessive result for Marrowfat Peas, but probably also Nobbe's abnormal
estimate for Faba vulgaris.
NOTE 2, A (p. 30).
Comparison of the weight of a leguminous seed dried under ordinary air-
conditions after swelling for germination with its original weight in the
resting state.
THERE are several disturbing causes that would come into play in
drying a seed that has swelled for germination. In my own experi-
ments only those seeds were accepted which had proved their
germinative capacity by displaying evident signs of the earliest stage
of the process. Owing to the slight growth of the radicle thus
involved, this would slightly increase the weight of the dried seed.
However, on comparing the weight of seeds just before and just after
the first signs of germination, I find that the correction to be applied
rarely exceeds 0-5 per cent.
This increase, however, would be counterbalanced by the slight
decrease in weight during the swelling process arising from the loss of
solid materials which pass into the water that dampens the surface of
the swollen seed. This is evident enough when seeds are allowed to
go through the whole swelling stage immersed in water, especially with
highly coloured seeds, when the water is deeply stained, or where
colloidal substances in the coats ooze out as mucus or slime. Easily
, APPENDIX 467
permeable seeds like those of the Broad Bean (Faba vulgaris) would
experience a noticeable loss of solid material when swelling in water.
Yet Nobbe (p. ill) in his carefully guarded experiments on the
swelling of these particular seeds in water found that the residue left on
evaporating the distilled water employed amounted only to 2*3 per
cent of the weight of the resting seed. Immersion in water, it should
be remarked, is not Nature's method of procuring germination ; and no
doubt the loss is much exaggerated in such experiments. In my own
experiments, where the seed was placed in damp moss as soon as it began
to increase its weight in water, such a loss would be much diminished,
and with most hard-shelled seeds it would be almost nil. However, with
some seeds it is nearly impossible to obtain a good result. Thus it is
with those of Adenanthera pavonina^ where a gelatinous material escapes
from the puncture in the coats that is required to induce germination.
Then, one may add, it is very difficult to prevent a slight loss in the
case of seeds like those of Poinclana regia and of species of Guilandina^
where the cuticle is apt to scale off. On the whole, however, I
consider that the disturbing influences in such experiments tend to
counterbalance each other. This remark also applies to hygroscopic
variation of a seed's weight in response to atmospheric changes, if
the seed is kept under observation for some days after the drying
has ceased.
As regards the mode of conducting such experiments, it is obvious
that much depends on the uniformity of the conditions of drying,
which should be carried out in a room but little affected by artificial
heat, except in the case of damp weather, when the seed may be placed
at first in a warm, dry room.
Most of my results on entire seeds are included in the table
subjoined. The effect of hygroscopic variation is excluded by taking
the mean weight for a few days after the drying has reached its
minimum. A column is added for the periods required to reach the
minimum, the drying period corresponding roughly to the swelling
period preceding germination, since a seed that swells quickly would
also dry quickly.
Conclusions to be drawn from this table are confined here to
immediate inferences that can be legitimately deduced from its
inspection. Remarks on the bearings of the data here arranged will be
found under the reference given at the head of the note. It is there-
fore sufficient to point out that although all these results indicate that
a seed swollen for germination returns when air-dried to approximately
its resting weight, there are regular variations both on the plus and
minus side, the ultimate weight being in excess in the case of
impermeable seeds, on the minus side generally with permeable seeds,
and variable in seeds where the permeability is a variable character.
4 68
STUDIES IN SEEDS AND FRUITS
TABLE SHOWING THE EFFECTS OF DRYING IN ORDINARY AIR
ON LEGUMINOUS SEEDS SWOLLEN FOR GERMINATION.
Weight in grains.
Effect of
drying
stated as a
Period
percentage
Permeable or
Species.
Resting
Swollen
for
After
of
drying.
of resting
weight.
impermeable
or variable.
seed.
germi-
drying.
nation.
Loss.
Gain.
Bauhinia sp. . . .
370
8-00
370
3 days
Variable
Entada polystachya, A .
5 '06
1270
5 '30
4
47%
Impermeable
' B .
7'i5
15-90
7'2S
4
i'4%
Variable
,, scandens
312-50
728-00
318-70
!9
*'%
Impermeable
Erythrina indica
1 2 '00
31 -60
12*30
4
2'5%
Variable
Faba vulgaris, A
41-50
86-30
40*60
5
* : *%
Permeable
.,, B . .
28-60
53'5
27-00
4
5'6%
...
Guilandina bonducella, A
44-16
124-60
46-90
12
4'o%
Impermeable
B
33-35
97'3
35-35
II
6-0%
Mucuna urens, A .
88-00
176-40
92-40
J 3
5'%
,,
B . .
87-40
174-00
89*20
12
...
*-i%
Phaseolus vulgaris .
13-50
24-60
'3'35
3
i'i%
Permeable
Pisum sativum
6'oo
14-30
575
3
4-2%
Poinciana regia
870
19-50
870
4
Variable
Note. Variable seeds are those sometimes permeable, sometimes impermeable.
NOTE 2, B (p. 29).
A further proof of the mechanical nature of the swelling process of seeds
indicated by their ability to proceed with germination when dried^ after
absorbing most or all of the water required for germination.
(THIS proof was omitted on p. 29, and has been added since. It is
illustrated in the following table by the results of my experiments
on the influence of previous swelling and drying on the germinative
capacity of different seeds.)
Knowing from the results of previous experiments, as given in the
table on p. 24, the swelling limit indicated by the maximum weight
attained before there were any external signs of germination, I was
able to conduct the experiments -accordingly. In the case of the seeds
of Hura crepitans I repeated the experiment on the same seed, but the
seed in the instance of two experiments rotted.
APPENDIX
469
Maximum
Total
Weight of
resting seed.
Weight of
the swollen
seed.
Weight after
being slowly
air-dried.
weight after
being placed
in water and
then in
Result.
duration
of
experi-
wet moss.
ment.
Guilandina
30 grains
7 1 grains in
3 1 grains
9 1 grains after
Germi-
4 1 days
bonducella.
3 days
after drying
swelling for
nated
for 32 days
6 days
Abrus pre-
i'S .
3 grains in
i '4 grains
3 grains after
Germi-
'3i
catorius.
21 hours
after drying
swelling for
nated
for 1 1 days
36 hours
Abrus pre-
!'5 ,i
2 '7 grains in
i '2 grains
2 '8 5 grains
Germi-
'4l ,,
catorius.
22 hours
after drying
after 45
nated
for 1 2 days
hours
Canavalia
9 7
23*3 grains
9-7 grains
22 '3 grains
Germi-
iof n
obtusifolia.
in 2 6 hours
after drying
after 40
nated
for 8 days
hours
Canavalia
20-0
45 grains in
20 '5 grains
46 grains after
All ger-
2i ,i
ensiformis
24 hours
after drying
36 to 40
minated
(average for
for 1 8 days
hours
three seeds).
Hura
22-0 ,,
41 grains in
2 1 's grains
46 grains after
Germi-
21 1,
crepitans.
2 days
after drying
7 days
nated
for 1 2 days
Hura
21'5 ..
41 grains in
2 i grains
42 grains after
Germi-
23 ii
crepitans.
2 days
after drying
9 days
nated
for 1 2 days
With the exception of the last-named plant, which belongs to the Euphorbiaceae and
has albuminous seeds, all are leguminous and have exalbuminous seeds.
The time occupied in attaining the maximum weight was the time required for ger-
mination, as indicated in the "maximum weight" column.
These experiments should be of interest to the agriculturist. At
the time they were made I was not aware that Professor Ewart had
several years before experimented upon the effect of previous swellings
and drying on the germinative capacity of Peas (Pisum sativum). The
seeds were well soaked in water and then slowly air-dried. After the
first soaking and drying they all germinated. After the second
soaking and drying only 40 per cent, germinated when the integuments
were entire, but all germinated when the integuments were broken.
Seeds subjected to a third soaking and drying failed to germinate
whether the coats were entire or broken (Trans. Liverpool Eiol. Soc. y
1894, viii. 207).
STUDIES IN SEEDS AND FRUITS
NOTE 3 (p. 31).
COMPARISON OF THE RELATIVE WEIGHTS OF THE COATS, KERNEL, AND
EMBRYO OF RESTING SEEDS, AND OF THE SAME SEEDS DRIED AFTER
SWELLING FOR GERMINATION. THE SEED ON DRYING RETURNS AP-
PROXIMATELY TO ITS ORIGINAL WEIGHT.
(With the exception of Hura crepitans, which belongs to the Euphorbiacese, all the
seeds are leguminous. )
Relative weight of the
separate parts, taking the
Albumi-
Permeable
entire seed as 100.
Name.
nous or
exalbumi-
or imper-
meable, or
Weight.
.
nous.
variable.
Parts.
Resting
seed.
Dried
swollen
seed.
Canavalia obtusifolia . ]
Exalbu-
minous
Imperme-
able
1 2 grains
Coats
Kernel
27-0
73-0
29-0)
7i 'of
Entada scandens . }
>
ii
4 ,
Coats
Kernel
49-0
51-0
49 -o )
Si-o)
Erythrina coralloden- I
dron |
n
Variable
3
Coats
Kernel
33'o
67 'o
35 ' I
65 -of
,, indica .
M
ii
12 ,,
Coats
Kernel
30-5
69-5
29-0)
7i 'of
Faba vulgaris . . -{
Permeable
35 ..
Coats
Kernel
14-0
86-0
H7 I
5-J 1
Guilandina bonducella -{
n
Imperme-
able
40 ,,
Coats
Kernel
58-0
42-0
57 '<> I
43 'of
Mucuna urens . . !
it
9 .,
Coats
Kernel
26*0
74 -o
25-0)
75' >
Phaseolus vulgaris . -I
ii
Permeable
2
Coats
Kernel
6'2
93-8
6-6 >
93*4,1
Cassia fistula . . |
Albu-
minous
Variable
4
Coats
Albumen
Embryo
15-0
66-0
19*0
20 '0\
60 "o J-
20 '0 J
grandis . A
n
9 n
Coats
Albumen
Embryo
25-0
64-0
II '0
2 5 '\
64-4 }-
10-6 J
\
Coats
29*0
28-0 )
,, marginata . <
a
1 ,,
Albumen
58-0
59 'of
I
Embryo
13 o
13-0 )
(
Coats
49'S
45'3)
Poinciana regia . . <
ii
ii
10
Albumen
23'5
*971
1
Embryo
27*0
25-0)
(
Coats
2 3'5
2 3'7 )
Bauhinia sp. . . 4
>
4 ,.
Albumen
4i'S
42'3 }
\
Embryo
35 'o
34'
(
Coats
30'o
29-0 1
Hura crepitans . . <
M
Permeable
20 ,,
Albumen
61-5
6i'6 >
1
Embryo
8-5
9 '4 J
Remarks on the table. Only approximate results can be expected
here, since we are not able to compare the relative weights of parts in
APPENDIX 471
the seed dried after swelling for germination with those of the same
individual seed in the resting state, but only with the average for a
number of resting seeds. We are indeed merely comparing an average
with an average. Then we have seen in Note 2, A that impermeable
seeds when dried after swelling for germination are heavier, and perme-
able seeds lighter than in the resting condition. Still, the results given
below will tend to emphasise the view that the swelling of germination
is essentially a process of water-absorption. This matter is dealt with
again in discussing the general mechanism of the shrinking and swelling:
processes in Chapter IX.
NOTE 4 (p. 43).
Experiments of Victor Jodin on the germinative minimum of Peas (Pimm
sativum) y from " Les Annales Agronomiques" October 1897.
THE peas were placed on a support of platinum suspended in air
saturated with water-vapour. By these means the water-vapour was
condensed in fine drops, and thus communicated to the peas. A similar
experiment under the same conditions, but in which the peas were
placed on a support of cork, gave no germination result, even after
55 days. In this last case the seeds had absorbed water in varying
degrees from 22 to 42 per cent, of their weight, but they had
failed to reach the germinative minimum of 67 per cent. This
investigator states his results in terms of the hydratation of a seed
that is to say, as a ratio of the dry and not of the wet weight ; and it-
has been necessary to convert them into percentages of the weight
of the resting seed.
NOTE 5 (p. 69).
Canavalia ensiformis^ DC.
Canavalia gladiata^ DC.
THE seeds chosen by me as the type of permeable seeds in
Chapter IV belong to C. ensiformis, DC., with white seeds. In his
Flora of the British West Indian Islands^ Grisebach gives C. gladiata^
DC., as having two forms or varieties : (a) with rufous brown,
and (b] with white seeds (C. ensiformis proper). I experimented on
both forms, the (a] form possessing seeds with varying degrees of
impermeability, the () form with seeds typically permeable. In this
work I have applied the specific name of C. gladiata only to the rufous-
brown or red-seeded variety, reserving that of C. ensiformis for the plant
with permeable white seeds. Professor Ewart in his paper (Proc. Roy.
472
STUDIES IN SEEDS AND FRUITS
Soc. Viet. 1908) places the seeds of C. ensiformis amongst his "macro-
biotic" seeds with more or less impermeable coats (p. 200). But in
the entry in his tables (p. 35) he says that five out of six seeds swelled
without assistance. It is, however, evident that his use of the specific
name C. ensiformis covers both varieties as well as others, and therefore
includes both permeable and impermeable seeds.
NOTE 6 (pp. 71, 166).
The influence of the coverings on the drying of permeable seeds. (See also
Note 12 on the time required for drying.}
THIS is by no means an easy subject, since the drying regimes of
seeds vary much, and an experiment very simple in its operation may
be influenced by a number of antecedent conditions. Some oily seeds,
like those of Ricinus communis^ are but slightly, if at all, affected in the
freshly gathered condition by the removal of the coverings. Thus in
the case of two samples of seeds, one just collected from the fruits, and
the other gathered seven weeks before, the bared kernels showed no
loss of weight, but merely varied about i per cent, in response to the
changes in the atmospheric humidity.
On the other hand, the coverings may be inert in their influence on
the drying process, as in the instance of seeds containing in the fresh
state an abundance of water. This is the case with the seed of the
Horse-chestnut (Msculus Hippocastanum\ which, when freshly gathered
from the dehiscing capsule, contains about 48 per cent, of water, and
dries, as shown in the results given below, more quickly and more
completely in its coverings than when it is bared.
DRYING OF SEEDS FROM THE DEHISCING CAPSULES OF
THE HORSE-CHESTNUT.
Condition of the seed.
Original
weight
Weight after
10 days.
Weight after
5 months.
Weight after
2 years.
A. Dried as bared seed
IOO
67
63
60*5
B. Dried in its coats, which
100
62
57*5
55
are included in the
total weight
C. Dried in its coats, but
IOO
60
55
52
weight of coats not
included
The weight of a moist seed varies from 200 to 240 grains. In the case of C. I have
deducted the weight of the coats ; 25 per cent, in the first, 27 per cent, in the second, and
28 per cent in the third and fourth columns as obtained from other seeds.
APPENDIX 473
In the Horse-chestnut seed the peculiar drying regime is connected
with the closely adhering absorbent tissue of the inner coverings, which
readily take up the kernel's moisture, and allow it to escape through
the large unprotected scar. The soft, swollen, white unripe seed,
when passing into the resting stage, mainly dries through the scar,
which occupies about one-third of the surface, and is not covered
by the ultimately impervious skin that protects the rest of the
seed. Long after this outer skin has undergone browning and
hardening during the shrinking stage, the scar remains moist and
gives off water. The relative impermeability of the brown skin
of the resting seed is well displayed by allowing the seed to soak
in water for a day or two. On examination the inner coverings
are then found to be saturated with water, which oozes out through
the scar.
It would, however, seem that the peculiarity in the drying rdgime
of the Horse-chestnut seed is in degree rather than in kind ; and indeed
it probably represents in an exaggerated fashion the behaviour of a
typical permeable seed. It is apparent from the researches of Becquerel
that the permeable integuments of peas (Pisum\ lupines, and beans
(Faba) after a certain amount of artificial desiccation become impervious
to air, except when it is saturated with moisture. This implies a
sluggishness during exceptionally dry atmospheric conditions of the
coats of permeable seeds ; and it may well be that such seeds in the
resting state are most pervious at the hilum or scar. If also we are
able to consider seeds rendered impervious to air by artificial desiccation
as in process of becomin 
