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 seed.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° Per 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. nected 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. that j made 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 Lebbeky 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 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'8S Variable. Artocarpus incisa (Bread fruit) . Artocarpeae 45'° 2 '22 Permeable. Arum maculatum Aroideae °'5 I-63 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 2°IO 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'° '23 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 tvv '934 j} Pisum sativum (Peas) „ 2*068 /(a) 1*960) pp. II9, 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'*878 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 mechanical6 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. 3o 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 !fter 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 seedreS 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 64'4 ,, 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±ouTgi"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 2-05 Poinciana regia 13 2-24 2'44 2-32 Canna indica . Cannacese 8 I'43 I '5» 1-48 shrinking and swelling1 ratios in different species. The great The next point to notice is the great contrast which the between the seeds 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.eP/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 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 5c 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 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. vivecj 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- 0fGuilandina tions and experiments, I will take the very divergent behaviour, anddCana* 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.) 69 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- 72 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 Of 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/garisy 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 0 § i •£ " • • 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 from 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 embryo. 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 leguminous0 sPecies 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- able™eeds.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. of the 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, 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 Process 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 aPpan- 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-^" '&.S0 •*-* rf O rt •ii '•« •o £ 0 «« "C v 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 of6 these seeds exhibit the extreme behaviour of the perme- variable a^le 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. I24 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 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^jjJjJm7 namely, in the variable group. But even here, as indicated seeds of the in the table, we must be able to distinguish between samples wherePb°th 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^dnSg0 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 i34 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 tab°e.°^ " 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 >-> M*J £. x n j; v« 1 s . -JJ J js 1'S . . ."a, . ."B. t>S CJ fl) ••-« *+"• rH S£ S^j g ^Ci'I in in 8 ^ *• "- f, ~ TO TO O ^J rz5 r^ *^ v w5 w5 53 t*i v> " " *A " * I O O~O~OMM • -O - ' • -O — -S £,-3 £ ~ °o g ^ v-^ rt* -5 K ^ ^ _C M £ g^-o y, g3 o£ a A t^vo 0 0 ONM m 0 0 ^i ^ "^.S 1> -a ° O a N VD r^c» o M m : : <^» : : : : *• -d-i -g « ^sE"" ^ c ° o So SHcq M M M M •"Js^o ^-^uS p T3 ° -G O in &* o 2 *~* o o ^j rt n vrioo ONtxiiOvO «0 r^ O j5 ui •* t) 0 oo1S"oo"2«3':S': : : :g C ^ ^ ^ ^ ^^ rt j^ ^ O/) rt — « Q J^ M^i-ooONiot\(*lOON O *J^ r< t^^O O oo M ro u^ tr^so w> • • ^ O OOOiiOi-iMOOOO ' 'DO ^ 'o oo«OOsvr,osroN 10 i^ 1 d B 4> IH 1-) a A IH r 91 s .u | .•§, | . i^rti/) u^rtin 1^. rt u -S 6^ „ S *•* oj t/i ^ "3 g rt 5 ^ a u 2 s p : : : : o\ O oo o" : "o : : : T3 ~- ^ .Q S u o ||I| <3 p : : : : 0 o "• o : : : Sill 3-Sal* ^•^•g u. ^2^,13 "^ 3 « v2 rt C C «o- (3 rt j - : • '• ON o • o • • • 2 w u C e3 o ro O V : : : "o o • - o O 0 0 O O O g.~-.a> 13 ^ v o 111 OS p p ft p p O O 0 0 O O O O O O O 1 I ^ :!.::'« r*"* *4- 8 3 ON *M ^ SL § M ? £• l ^ ° § ° ^N HH C; 5 ; § r : H O) . H ra m rt . ^^ U ° -5J 1 " s s = = r = JJJJ J d J J d J d "*^ g G «° ° o ?! •& v & •g g J2 Q, C/3 v. fi, rt G rt J* 'i •*" §* % - G >< J (X «<•<<« U "G c U H p w III CO t, o H U H K H O ADDITIONAL EVIDENCE 137 in _CJ >, _tj ju -5 lete. when quite o u _rt ff§ | O.J 3 "3 5 bo i> c 3 .0 g •?>'i'| ^ci Q °* <*~ o o vo OO oo t^ vo TJ- n t^oo O O N •*• : ::::::: ^ <*> t-^ : o> : : : IC^OOOOOOOOOOON: oo : : : : M M M « f-P .-*.N^P^P Si::: o o • o f«1 Th w U-»00 O«^NNt\txO 00 o o> : ::::::::: N : •* vo tovo r^ to « ON rn t^ t^oo ^o : ON : • : : : VO M ^ OO •^•oo OO tx O N v>^O tx O O ^ » 'H, : :::::::::«-.: rj- tot^^M^Tj-c-iTj-mtr,^: : w: : : : M 00 H . 000 . .0*00 ^0 0 ^ VO HI HIHIHIMHIMHIHIH, H, H, _ H, u •9 JD C cit > C V Jh-U JhJ'hJ'JnJJ : : : :4 h-1 J'-llJ|-1 § 13 s 3 1 to . C . . . -3 ... ... Erythrina coralloder , , indica , , velutina « rt| g-| s 2 ' 1 -1 2 « § rt ^ '" -^ i'1| J||||l|Ii N-Ill ^O ^rrt WQ ^r^oo Ctf£3 f^ tl/J -.^S 'ac ^^JSrtr-CiJ M°i5^^w 111 =11 sl 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 such 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 no0 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 98*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. ISO°F. 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 CS ~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 i44 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 ioc 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 uia 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 5o 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 3I-3 32-* 28-0 29-4 31-0 29*6 3!'4 33'o 34'5 32'9 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. hhgro-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 no0 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 X7*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^ds8*" inference is that it had not completed its drying in air and thefe 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 i56 STUDIES IN SEEDS AND FRUITS The view of Becquerel. Schroder's experiments. the air has the potentialities of immortality (Comptes rendusy 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's6 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. i58 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 » • ,. 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 S 13 "S (J £§• **- O 1-1 a, : OOOO OOOOOvOO 0 0 C *•' * J3 O to "> ONOO ^h O OO u-i rj- V^IOO O O OO «n '*"' o •*- a, o o tn WTHO-h Th mvo w,vO N •* »rt *VO 9 |S|1.1i|l| tn . vn *•:•;•: p *" p vp TJ- vp o O en « 1 "rt •3 T5^ • *H >*» jj TO ^ qj O -|^ p . oo oo : f> VO t-^ C^OO oo p p O p O O O O O OOO O t-* t^ O O O en 3JS--SB M ON w O 1^ O M oo M o vo TJ-VO o O tn M o •" o c_o E"1 .S ° o •" ^- °~-s -«s ZX23ZZZ .d Sf|°5o' •*•„.» t^ 1- t^ 0 r^ 0 ON N ONO rhvo ^ O O r- ON 1 D Oi in lyivsi5! OO OO D O 00 M ro IT^ ^ S^ M^> ^ ^? 5- 5 V .S? 'C g » s '-3 >, S jj O . N vO vo »n en HOO OOOOOOO "o !* a; S 'MJ- ^" 'S c .'§°'C "" '° c .2 OOO OOO OOOO OOOO OOO OOOOOOO OOO OOOOOOO ^ £~ S y - * 13 0) in V en ,c S*« * .22 u Jll in tn yj qj „_. O in 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 T1 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 Process- 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 Z3'5 24 'o V. Bignonia (near sequi- Bignoniacese 5'° 2-30 38*0 28-0 ... p. noctialis) Csesalpinia Sappan Leguminosse 10*0 2 '2O 32'5 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 32P8 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 ... 3I-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 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 46 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. I1811*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 '91 Phaseolus multiflorus Iris foetidissima L. p. p. 2-08 2-07 r , Pomciana regia L V. '91 Faba vulgaris . L! p. 2-05 Csesalpinia sepiaria . Entada polystachya . L. L. V. I. '91 '91 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. 2i4 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 Elf 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 24o 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'S2 ,. 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'31 » 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 91 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 attention> 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 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 25 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 30 IOO 30 70 Entada polystachya H 800 240 IOO 30 70 Csesalpinia sepiaria 5 IOO 3* IOO 32 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 13S 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 29 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 3Z 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^in0 in the full-grown living condition on the plant. Amongst the llvinf> 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"tingSthe 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?ustrate^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 32 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 Z4i » 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 >, 24 »» 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 Ai_ 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 2y6 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]^jajjcd 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, belong1 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, C2 » 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 I233 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 dfy 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 52 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) (C25 * 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 302 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 25 IOO ... 149 91 240 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 702 648 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 46 44 56 IOO 17 40 57 30 70 IOO 5 21 26 19 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 48 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 . 46«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 3o6 STUDIES IN SEEDS AND FRUITS Explanation Though these tables largely explain themselves, a few of die tables. eXpianatOry 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 f the tab e. ^^ ^e acorns of the 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 (32 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 51 '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, J71 45'5 48-6 ... 18-1 S2-9 25'5 74'5 "Vital connection 64 57 "4 >» X4 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 3i2 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 sPeclosa- 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 3i8 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 ) ( „ PseUdacoruS}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 : (» 700 I 70 40 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 48 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 52 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 25 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 25 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 25 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 71 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 65 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 withered 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 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-65 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 [// 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? 17 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» 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 388 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) 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 restmg 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 seedy 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 Plants- 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 396 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. features in 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. 398 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- the seecjs 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 their8 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 4o4 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 • i r • j • of Cocos and is more or less in a state or saturation as regards its nucifera. water-contents, since on being placed in water its weight 4i2 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 4i4 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 Eli-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^ Quercusy 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. 424 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 seecj an(j fruit 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. 426 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- 4'96 » •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^emliryo01 with the berry and the embryo grows with the seed, the °,f the ljy 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. 432 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 that germin- 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 436 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, 311- 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 onty 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 °jn rees' In an article on " The Dwarf Tree Culture of Japan " by Mr Jjfut^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