THE INDIAN ASSOCIATION
FOR THE
CULTIVATION OF SCIENCE
1. THE R O Y A L BOTANIC GARDENS, KEW .
In relation to the Empire, and to India in particular.
2
.STUDIES IN THE GERMINATION OF SEEDS.
BY
S ir A R T H U R W . H IL L , K.C.M.G., Sc.D„ D.Sc., F.R.S.
Director, Royal Botanic Gardens, Kew,
based on Lectures delivered as Ripon Professor f o r the y e a r 1 9 3 8 .
[ All copy rights reserved, j
H 5 5 R
9Z9^
y f ! )
C A L C U T T A 1939
Price R s. I /5/- or 2sh. Nett.
THE INDIAN ASSOCIATION
FOR THE
CULTIVATION OF SCIENCE
1. THE R O Y A L BOTANIC GARDENS, K E W .
In relation to the Empire, and to India in particular.
2. STUDIES IN THE GERMINATION OF SEEDS.
BY
S ir A R T H U R W . H IL L , K.C.M.G., Sc.D., D.Sc., F.R.S.
Director, Royal Botanic Gardens, Kew,
based on Lectures delivered as Ripon Professor f o r the y e a r 1 9 3 8 .
All copy rights reserved.]
I A C S
III
92 93
C A L C U T T A 1939
Price R s. I j 8 l - o r 2sh. Nett.
PUBLISHED BY THE INDIAN ASSOCIATION FOR THE CULTIVATION OF SCIENCE 210, BOWBAZAR STREET, AND PRINTED BY S. B. M ALLIK
AT BANI PRESS, 16, HEMENDRA SEN STREET, CALCUTTA
Indian Association for the Cultivation of Science.
The Royal Botanic Gardens, Kew, in relation to the Empire, and to India in particular.
Being the first of three Lectures delivered at the Indian Association for the Cultivation of Science by Sir Arthur W, H ill, K.C.M.G.^ Sc.D.^ D.Sc.^ F.B .S. Director, Royal Botanic Gardens, Kew, as Ripon Professor of the Indian Association for the cultivation of Science for 1938.
The Royal Botanic Gardens, Kew, which are now the National Botanic Gardens and the headquarters of botanical work for the Empire, have only been a National Institution since the year 1841 — they are thus much younger than the Royal Botanic Gardens, Sibpur, Calcutta, whose one hundred and fiftieth anniversary was so appropriately celebrated last year during the meeting of the Indian Science Congress held at Calcutta. There is a close parallel between these two famous Gardens since they are both situated on the banks of the great rivers which flow through the capital cities : Sibpur by the side of the Hoogly, within a few miles of Calcutta, the second city of the Empire, and Kew on the Banks of the Thames, some seven miles from London.
Both Gardens serve as centres of botanical research, thanks to the richness of their collections of living plants, the historical import
ance of their herbarium and museum specimens and their valuable botanical libraries. The Gardens also, being full of beauty as well as of botanical interest, serve for the inspiration and recreation of the peoples both of India and the British Islands. The Calcutta Gardens and Herbarium, like those at Kew, should also be visited for pur
poses of study and research by all students of Indian Botany, whether in India or on the Continent of Europe or elsewhere.
Jl -t J ,
Kew again owes its origin to private enterprise, hs does the Sibpur Garden, for it was due to the interests in botany and horticul
ture of Princess Augusta of Saxe-Gotha, the mother of H. M. King George III, that a botanic garden was set up at Kew after the death of her husband Frederick Prince of Wales, in 1 759.
With the help of the Earl of Bute, as her‘Botanical Adviser, the Princess made a garden at KeW of some 1 5 acres and p lan t^ it with many interesting trees and shrubs, some of which still survive, notably the fine Maidenhair tree {Gingko biloba), which is now the finest specimen in England. Princess Augusta also emplo5^d the well- known architect Sir William Chambers to design and erect several Temples according to the fashion of those times, some of which are still standing, and also the Pagoda, so well-known a landmark to all visitors to Kew. Alongside “Kew ‘ Gardens** the^ demense of Princess Augusta which stretched, from Kew Green towards Richmond, there was another. Royal garden, on the riverside, extending from Ormonde Lodge in Richmond Deer Park to Brentford
■ •
Ferry at Kew, the property of George 11 and Queen Caroline. The two Royal gardens were separated by a public road—Love Lane—
which led from Richmond to Brentford Ferry where the Thames could be crossed in the early days before the bridge over the river at Kew was constructed.
On the death of Princess Augusta and of Queen Caroline ,King George 111 inherited both these Rbyal gardens and later obtained leave to move the public road (Love Lane) to the east of “Kew Gardens** and so united the two gardens into one domain. It is because Kew consists of two gardens united together that we use the plural title “Royal Botanic Gardens**. The position of the old Love Lane may still be seen in the straight “Holly Walk’* lying to the west of the present Temperate House.
George 111 took a great interest in Kew, where he frequently resided, and with the assistance of Sir Joseph Banks who was his Botanical Adviser and for many years President of the Royal
Society, he established the many connexions between Kew and the Colonies which have been so fortunately continued down to the present day.
Between 1760 and 1820, the year in which both George 111 and Sir Joseph‘ Banks died, expeditions with botanical collectors, who were men trained at Kew, were sent to Australia, South Africa, South America, the West Indies, China, India and other parts of the world.
Botanic gardens were also established in the Colonies, that at St.
Vincent being the earliest, and plants of economic and horticultural interest were brought back to Kew by her collectors and sent out from
Kew to the newly-established gardens in the Colonies.
The Calcutta garden, founded by Colonel Robert Kyd in 1787, was a frequent recipient of plants from Kew, not only in those early days but on many subsequent occasions, whenever, any plants likely to flourish there came to hand.
Kew in those early days not only received large collections of living plants and seeds from all parts of the world, but also large collections of dried plants—herbarium specimens—which were the private property of Sir Joseph Banks. Since Kew had no Herbarium of its own, Sir Joseph, on his death, bequeathed them to the British Museum and these early collections made by botanists sent out from Kew formed the nucleus of the botanical collections and Herbarium of the British Museum, and are now to be found at the Natural History Museum, South Kensington.
With regard to the living plants, it is of interest to remember that the South African Pelargoniums—now so well-known as our familiar garden “Geraniums”, Cinerareas, the Chilian “Monkey Puzzle” (Araucaria)^ the British Columbian Douglas Fir {Pseudolsuga taxJfolia = P. DougIasii\ and many other well-known garden plants and trees were introduced to British gardens and thence to gardens througout the Empire towards the latter end of the 18th Century.
Coming to recent times 1 may mention that the Bougainvillea
“Mrs. Butt”, so commonly grown in gardens in India, was sent
out by Kew a few years ago. This plant 's^ras discovered in a priest’s garden at Carthagena, Colombia, by Mrs.* Butt, wife of one of the bank-managers in Trinidad, and was sent by the Trinidad Botanic Gardens to Kew, where it was propagated and distributed to India and other parts of the Empire.
After the death of George III and Sir Joseph Banks, Kew received but little attention, though some * collectors were still sent overseas, and at the end of the reign of William IV it was doubtful whether the Gardens would be maintained. Thanks to the efforts of the Commission set up shortly after the accession of H. M. Queen Victoria, which included Sir Joseph Paxton and the Rev. W. Lindley, it was decided to establish the Gardens as a National Institution and in the year 1841 the Royal Botanic Gardens, Kew, came into existence as the centre for botanical enterprise and research for the Empire.
Sir William Jackson Hooker, the then Professor of Botany in the University of Glasgow, was appointed the first Director in i 841 and he very wisely continued the development, of the Gardens on the lines established by Sir Joseph Banks and George III, and greatly extended their influence and value. He was, among other things, impressed with the desirability of bringing together exhibits of plants and plant products of economic importance ; that is, the plants which contribute so largely to the necessities of our daily life, such, for instance, as tea, coflee, cacao, sugar, foodgrains, drugs, spices, textiles, fibres, cotton and the likel For this^ purpose he set up the first museum of economic botany in England, in a building at Kew which had formerly been the Royal fruit store. .This building is still in use as our Museum no. II, at the north end of the Gardens and is devoted to the plant products furnished by monocotyledonous plants. From this modest beginning all other museums of this nature have had their origin and the Imperial Institute may well be claimed to be the magnificent outcome of Sir William’s wisdom and foresight.
Sir William Hooker, when he came to Kew, found no Herbarium in existence, since the early Kew collections were at
the British Museum, but he brought his own small private collection of dried plants with him from Glasgow and the case in which it was housed is kept as an interesting historical relic in our visitors’
room in the Herbarium. It was not long, therefore, before he pointed out the need of creating a Herbarium at Kew and persuaded Govern
ment to make over Hanover House, the residence of the late Duke of Cumberland—the King of Hanover—for the purpose. This was done in the year 1853, when the present great Kew Herbarium came into existence.
Suggestions have been put forward from India that some of the early Indian collections now housed at Kew should be returned to India. These early collections were made in the time of the East India Company’s administration. Some were made by private individuals, others by servants of the Company in their private capacity, others by servants of the Company in their official capacity who were permitted by the Directors to retain possession of them when they retired from their service, while others again were stored in the London offices of the East India Company and were finally handed over by the Court of Directors to Kew. Kew was not the only recipient of these early collections, for they are to be found scattered over the herbaria of Europe and in other herbaria in Great Britain.
Those that are at Kew were therefore acquired by purchase or by deed of gift and there can be no question as to their present ownership ; nor can there be any question that they are in their rightful place, considering that they contain many type specimens on which the Indian Floras prepared at Kew are based. It was largely on these collections and on those made subsequently that Sir Joseph Dalton Hooker, the second Director, wrote the great “Flora of British India”, while other authors have written the “Flora of the Bombay Presidency” (Cooke), the “Flora of Madras” (Gamble, finished by Fischer), and the “Flora of the Upper Gangetic Plain” (Duthie), based largely on the specimens preserved at Kew and on specimens sent to
Kew on loan by the Herbaria at Calcutta, Madras and Bombay.
But to. return to the Gardens and the distribution of plants of economic importance. The most valuable of the plants introduced to India through Kew were undoubtedly the South American Cinchonas, the source of Quinine, the specific remedy for Malaria, which is so serious a malady not only to the millions of the people of India but to the inhabitants of tropical countries throughout the world. The enterprise had long been advocated in India and Cinchona plants and seeds were eventually brought to Kew in 1861. Plants raised at Kew were despatched to India where they were established in the Sikkim Himalaya and in the Nilghiri Hills. It is from these original plants and from subsequent introductions that the flourishing plantations now existing at Mungpoo and Munsong, and in the Nilghiri and Anamali Hills, have been established.
The plantations in the Nilghiris were started by Mr. Mclvor, a Kew-trained gardener, and those in the Himalaya have been in the charge of Kew-trained gardeners almost since their foundation ; their present excellent condition is a fine tribute to the work done in the past and at the present time by the skilful and devoted band of men who have been in charge of these extensive plantations.
As the success of this profitable Sikkim undertaking to the province of Bengal is so dependent on good cultivation, it is to be hoped that the long connexion with Kew may be continued for many years to come, since any lapse in sound horticultural practice, through lack of skill or knowledge, would involve the Government in serious loss and lower the high standard of Quinine production which now obtains in the Bengal plantations.
Another important economic plant sent to Calcutta from Kew was the Para rubber plant, Hevea brasiliensis. This was introduced from Brazil to Kew in 1876, and it was hoped the plant would thrive at Calcutta, but unfortunately the climate proved unsuitable and though plantations are now flourishing in the South West of the peninsula, the original consignment sent to Sibpur did not result in any benefit
to India,
Among more recent introductions from Kew reference may be made to the Chinese Tung Oil, yielded by Jlleurites Fordii and A.
montana^ plantations of which in some parts of India are showing satisfactory progress. India has also rendered great service to Kew in supplying seed of Hydnocarpus^ the source of Chaulmoogra Oil, the specific for the scourge of Leprosy, and has thus enabled the Royal Botanic Gardens, Kew, to send out plants and seeds of these valuable plants to tropical countries where Leprosy is prevalent. Kew again has been very helpful to India and other part of the Empire in getting together and working out the classification of the many species of Sorghum, the seed of which is so valuable a food plant to the peoples of India, and has been able to suggest those forms which are of most value from the dietetic point of view. Similar work is in progress with the Cow Peas (Figna), and with other crop plants, oil seeds, etc., and in this connexion Kew is working in close co-operation with the Imperial Agricultural Research Institute at Delhi, the Research Institutes in the Provinces, the Imperial College of Tropical Agriculture, Trinidad, as well as with the Agricultural Depart
ments in the Colonies. All such work relating to economic products and especially to those on which the welfare of the people of India so largely depends for food demands the close co operation of systematic and economic botanists both at home and in India. As to the systematic side of the work, Kew more than any other institution, from her great resources and from her connexions with all parts of the Empire, is able to supply the information which is required for the systematic study of the races and varieties of all such crop plants.
Another recent development is in connexion with the supply of varieties and species of economic plants required by the plant- breeders and geneticists Kew, at the present time, is arranging the supply of varieties of the different species of Manihot (Cassava) from Brazil to the Agricultural Research Station at Amani, East Africa, where attempts are being made to find a variety resistant to mosaic disease Similarly species and varieties of Musa are being collected in various parts of the world, under the auspices of Kew, and are
then being sent via Kew to Trin^idad and Jamaica, for the genetical researches now in progress in connexion with the attempt to breed Bananas immune to Panama Disease ; while cuttings of high quality Cacaos are being sent from Trinidad to Nigeria. In all these cases it has been found necessary to propagate these introductions for a period at Kew, partly as an additional guarantee that these new varieties will not be lost, and partly to ensure that diseases and pests are not transferred by the agency of these new introductions from one hemisphere to the other. The quarantine arrangements at Kew are proving an essential precaution in these days of rapid transport.
Incidentally 1 may mention, among the services which Kew has rendered to industry, the identification of the tree from which the best cricket bats are made. Up till a few years ago there was no certainty as to the species of Willow which should be grown for the purpose.
Trees were selected by buyers for the cricket-bat firms ; men who, though they were unaware that Willow trees {Salix) were of two sexes, were yet able to pick out the best trees for making cricket bats during the winter, when the trees were leafless and showing neither leaves nor catkins ; doing so apparently by the character of the bark and by their habit, points which had not been recognised by the botanists. Specimens of the trees selected by a skilful buyer were collected both in leaf and in flower and it was then found at Kew that the trees selected were in all cases the female form of Salix coerulea. In consequence of the correct botanical identification it is now possible to obtain the proper plants to make plantings of the Willow most valuable for the manufacture of cricket bats.
The connexion of Botany with so many other fields of activity adds very greatly to the value and interest of the science. It may not generally be remembered that the occurrence of pepper {Piper nigrum) on the Malabar Coast was one of the main inducements which led the Portuguese to discover the way to India via the Cape of Good Hope in 1486, while the presence of cinnamon, native in Ceylon, and of nutmegs and spices in the Moluccas, etc., led not only to geographical discoveries but also to many subsequent struggles
for the possession of these valuable sources of supply of important vegetable products.
But to return to Kew—the administration of the Royal Botanic Gardens is centred in the Director’s Office, with four subdivisions : the Gardens, Herbarium, Museums and the Jodrell Laboratory, In the Gardens, under the charge of the Curator, plants representative of the Empire and of the world generally are grown in the open and under glass, as far as the climate of Kew will permit. It is of interest to find that the small Rhododendrons from the high mountains of Tibet, and the high alpine plants from the Himalayas, Bhutan and Nepal, will flourish and flower at Kew, which is situated almost at sea level, quite as profusely as they do in their native homes.
In the tropical houses the ferns are grown as far as possible under their natural conditions, epiphytes being grown on tree trunks and tree ferns with suitable undergrowth being planted out giving the semblance of a tropical forest. Similarly in the Sherman Hoyt cactus house and in the new South African succulent house the cacti and the succulents are planted out among rocks similar to those among which they grow in their native countries. In the cactus house the living collections planted among the rocks merge into a fine painted background of the Mohave Desert, California, in so realistic a manner that it is by no means easy to distinguish the dividing line between the rocky foreground with the living plants and the painted landscape behind.
As regards India, Himalayan plants are mainly grown in the open or in the Temperate House, while those from the tropical regions are to be found in the Palm House, the orchid houses and other of the tropical plant houses.
In two of the four museums at Kew the plant products derived from the Dicotyledons (No. I) and from the Monocotyledons (No. II) are displayed, while Museum No. Ill is given over mainly to exhibits of tropical timbers, including many fine Indian specimens. No. IV Museum, Cambridge Cottage, is devoted to exhibits of British-grown
timbers and their pests and diseases, as well as to an interesting display of articles made from the various woods, such as cricket bats tennis racquets, brushes of all kinds, tool handles, etc., showing all stages of their manufacture. It may be of interest to mention that the botanists in the museums, in conjunction with the botanists in the laboratory, are frequently called upon to discover the source of origin and botanical status of new plant fibres, which are from time to time put on the market to tempt the unwary investor. These usually are found not only to be inferior to such staple commodities as jute or cotton, but also to be misleadingly described and advertised.
Thanks to the extent of the collections it is generally possible to identify any plant products or timber specimens which may be sent to Kew for determination.
With regard to the Herbarium and Library to which reference has already been made, the herbarium specimens now number about 5,000,000 sheets, while the Library, which is probably as fine a botanical library as any in existence, contains over 50,000 volumes and periodicals, as well as a very extensive collection of botanical pictures, some of which are of great value. The Herbarium is now housed in three large extensions of the original Hanover House, and is arranged according to the system of Bentham and Hooker on geographical lines. It is thus an easy matter to study the Indian specimens in any particular genus, since all the Indian specimens, like those from South Africa, Australia, etc., are arranged together in covers bearing the label of their country of origin.
The Kew Herbarium is visited by botanists from all over the world and especially by botanists from the Uniled States and the Continent of Europe, while from time to time 'we receive visits from Australian, South African, New Zealand, Chinese and Japanese systematic botanists. The recent visit of Dr. Biswas from Sibpur has been a welcome innovation, which it is hoped may soon be followed by visits of other Indian systematic botanists.
Since Kew possesses such a wealth of historic herbarium specimens of South Africa, Australia, New Zealand, India and other
parts of the Empire, the Government of the Union of South Africa decided a few years ago to appoint a South African systematic botanist to come over to Kew as a liaison officer for about two years to work on our historic South African specimens, and then return to Pretoria, enriched by his experience, to be replaced by a successor to continue the work and gain fresh experience by working at Kew and other herbaria in the British Isles and on the Continent. Australia has now followed the example of South Africa in appointing a liaison officer to examine the Australian specimens at Kew and compare them with more recent specimens collected in the various States of the Commonwealth, and so settle many difficult questions of nomenclature and specific identity.
The Government of India has for a long time maintained an Assistant for India at Kew to deal with the many questions referred to Kew from India on matters of systematic or economic botany, and the time seems now ripe for India to follow the example set by the Union of South Africa and to send over one of her university graduates, well-trained in systematic botany, to serve as the Assistant for India for a period of two or three years working through our Indian collections, who on his return to India, richly stored with fresh knowledge and experience, would be replaced by a successor to carry on his work for the benefit of the study of systematic botany in India.
Reference must be made in conclusion to one other activity of the Royal Botanic Gardens from which India has benefitted so fully over a long series of years, and that is the training of student gardeners to fill important horticultural positions both at home and overseas.
Some twenty-five of these student gardeners come to Kew each year for a period of two years after they have received four years preliminary training in horticulture. During their period of study at
Kew, in addition to their practical gardening work, they attend courses of lectures in the sciences pertaining to horticulture, including insect-pests and fungus diseases of plants, and thus become fitted to
take up posts as curators of botanic gardens, such as Sibpur, superin
tendents of plantations such as the Cinchona Plantations at Mungpoo and Munsong, superintendents of municipal parks, head gardeners, and the like. Kew receives as student gardeners not only young men residing in the British Isles, but student gardeners from the Domi
nions and Colonies as well as from the Continent of Europe and from the United States of America
These overseas men now usually come to Kew on an exchange basis, a student from Kew going over to the New York Botanical Garden, to Berlin, Paris, South Africa or New Zealand &c. to take the place of one coming to Kew, for a period of one year in the case of Europe or two years in the case of the Dominions or the United States. Should it be possible to effect an exchange arrangement with India in a similar manner there is no doubt that this would prove of material benefit on both sides.
Many of those who have come out to India have left names that will long be remembered, and I may mention here only one or two who have rendered, conspicuous and meritorious service : Mr.
James Gammie, who eventually became the Imperial Cotton Specialist in India ; Mr. Woodrow, whose book ‘‘Gardening in India’* occupies the front rank of books dealing with Indian garden craft ; Mr. Lane, formerly Curator of the Sibpur Botanic Garden *, Mr. Proudlock ; Mr.
Griessen and his work at New Delhi ; Mr. Krumbiegel and many others.
It is to be hoped that India will long bear in m^nd the pioneer work which has been done by the long line of Kew-trained men who have done so much to promote the science and practice of horticulture in India, and who have done so much to build up and maintain the many fine public gardens which now exist throughout the Indian Empire. May India now train up a band of successors to these men, and as you have entered into the labours of others, so labour that others in turn may enter into yours,
LECTURES II AND III
Studies in the Germination of Seeds,
L ectu re II.—Some abnormal Dicotyledons.
The primary object both of plants and animals is the preserva
tion of the species and this, in the case of the vegetable kingdom is effected among the flowering plants, with few exceptions, by means of the seeds, which, as is well known, are produced in enormous
numbers.
In the case of most annual plants the production of seed is followed by the termination of the life of the individual, but if seed- production be prevented by constant removal of the developing fruits, an annual plant may become a perennial. This can be well shown by the common garden plant Mignonette {Reseda),
Seeds again are of two well-marked types. In the one case the embryo seedling is enclosed or surrounded by nutritive matter on which the embryo feeds after germination has commenced—these are the well-known class of the endospermic seeds, of which the coconut (Cocos), and the castor-oil seed {Ricinus),^ are familiar examples. The other class, the non-endospermic seeds, unlike the endospermic ones, have absorbed the endosperm provided by the mother plant before germination commences, and in these cases all the endosperm has been absorbed by the time the seed is ripe and is ready to be sown to start germination. The common gourds and vegetable marrows {Cucurhita) may be cited as examples of non-endospermic seeds.
Then again when germination takes place the cotyledons or seed leaves may remain within the seed and function purely as absorbent organs, removing the products stored in the endosperm and passing them into the developing plumule and radicle of the seeding, or in other cases, especially those of the non-endospermic seeds, the cotyledons usually emerge and expand in the air and become the first
145, 1.K ern el and Oliver, l^atural H istory o f Plants V ol. I, p. 599. figs. 141, 1 & 2 ; p. 611,
assimilating leaves of the young seedling ; in some of the Leguminosae^ however, though the seeds are non-endospermic the cotyledons are hypogeal.
In the case of the Dicotyledons, which include the majority of our flowering trees, shrubs and herbaceous plants, two cotyledons are borne by the young seedling, though there are some interesting exceptions to which I shall refer in detail presently.
The Monocotyledons possess only one seed leaf, and include the palms, bamboos and grasses, etc. With some of the palms 1 shall be dealing later, when speaking of the peculiar methods of germination of seeds enclosed in stony endocarps. Reference in passing must also be made to the Gymnosperms, especially to the genus Pinus, where there are several cotyledonary leaves, and also to those few cases among Dicotyledons where the two cotyledons may be divided into two or more lobes, as in Schizopetalon Wall^eru Eschscholtzia, Pterocarya and Tilia.^
Seeds, as is well known, vary very greatly in the time they will remain in a viable condition. In some cases, for instance the genera Salix and Populus and some Primulas, the seeds are able to retain their vitality for a few days only, and especially in this so in Salix and Populus ; for unless they are sown as soon as they are ripe they will fail to germinate. Others, though protected by only a thin seed-coat, such as many orchid or Lilium seeds, can retain their vitality for a considerable time, while oil-containing seeds as, for instance, those of Para Rubber {Hevea), though well-protected by a thick seed-coat, will retain their vitality only for a few weeks. The nature of the strength or otherwise of the protective seed or fruit-coats thus affords no reliable guide as to their powers of longevity and we have found at Kew that seeds of certain of the Leguminosae, not very strongly protected by their coats, which had been stored in the Museums at Kew for from 80 to 90 years, still retained their vitality and a certain proportion germinated normally when sown a few years
* Lubbock, J. On Seedlings, I, 51, 52, 128, 282 ; II, 521,
ago. The most striking examples of these were seeds of Anthyltis vulnerariCy which had been kept for 90 years, of which 4% germinated ; Trifolium striatum, also 90 years old, 14*1% of which germinated, whilst a fair proportion of the seeds germinated of Trifolium pratense and Lotus uliginosus, both 81 years old, and of Medicago orbicularis which had been kept in a bottle for at least 78 years.^
Some seeds are able to survive immersion in water for a considerable time, the protective coats of their fruits preventing them from being injured either by salt or fresh water. As a result such fruits, which have been carried by ocean currents and washed up on the shores of continents and islands, have been found to be viable and have germinated successfully in their new home. The presence of certain unexpected plants in a littoral flora may be attributable to this agency. Certainly the distribution of the Coconut has been brought about very largely by ocean currents and the recent finding of germinating Coconuts on Krakatau and Anak Krakatau, washed up on the sea-shore, is an interesting proof both of the resistance of the fruit and seed to sea water and of its ability to germinate in its new home.t
The record for longevity for any seed is probably held by Nelumbo nucifera Gaertn., for Ohga^ obtained about 100% germination with seeds which had been buried in a peat bed in S. Manchuria, and which were at least 1 20 years old and may probably have been 400 years old or older. Some of these buried seeds from Manchuria were received at Kew and germinated quite normally.
As a general rule seeds, when fully developed and shed from the parent plant, can be stored and kept for a shorter or longer time in a dormant condition, but a few exceptional cases may be noted where there is no arrest in the course of the development of the seed into the young germinating plant. The mangrove affords
* Turner, J. H. “The V iability of Seeds”, Kew Bulletin, 1933, pp. 263, 264.
t Leeuwen, W . Docters van. Krakatau, 1833-1933 ; Ann. Bofanij, p. 469 (1936) ; Hill, A. W . Natnre, Vol. C X X IV , pp. 135 & 507 (1929) ; Vol. C X X X IX , 135 (1937).
t Ohga, I. “On the Longevity of Seeds of Nelumbo nucifera”, Bot. Mag. Tokyo Vol. X X V II, pp. 87-95 (1923), and Turner l.c. p. 261.
Typhonodorum Lindleyanum Schott.
Fig. 19. A young fruit, showing the white, horny pericarp, attachment scar and also stlgmatic surface. Nat. size. 20. A similar fruit, in longitudinal section, showing the haus- torial position of the cotyledon, with some of the protuberances, attached to the corm-like body by a narrow neck. A t the top, the developing plumule can be seen, x 2. 21. A n older fruit in section, showing a considerable development of the numerous plumular leaves lying in a curved position at the apex of the corm-like body. The root apex (r.) can also be seen, x 2. 22. Longitudinal section of a seed which has become free from the pericarp, showing the leaves of the plumules expanding and a developing root. This was taken from a spathe, and shows the condition in which the seeds are dropped into the water. Nat. size.
23. A mature seed taken from the spathe with the pericarp still attached and hiding the haustorial portion of the cotyledon. The plumule is becoming freed from the groove of the
“corm” in which it lies when developing. Nat. size. 24. A young seedling, side-view, libera
ted from the spathe as it floats in the water, showing the haustorial portion of the cotyledon at the base, the large obovoid, corm-like body and the young plumular leaves and roots. The young leaves show no trace of a lamina. Nat. size. 25. A sirnilar seedling seen on edge showing the groove at the apex of the corm-like body in which the plumule lies when the seed is enclosed in the pericarp, cf. Fig. 22 apex. Nat. size. 26. A n older seedling showing the development of a lamina on the older leaves. The seedling has become rooted in the mud.
(from 'Annals o f Botany' Vol. XLIII. p. 446).
the best example of this continuous type of seedling development.:^
Here there is no resting period but the embryo contained in the inverted, pear-like fruit continues to grow and the radicle eventually grows out through the apex of the fruit at the expense of the food material stored in the seed, until finally it becomes severed from the cotyledons and, carrying the young plumule at its apex, falls into the water and floats upright until it comes to rest on the mud flats of the mangrove swamp. Typhonodorum, the giant Aroid from Madagascar, behaves in a very similar manner, except in this case the whole seed with its well-developed plumule and radicle falls from the decaying spathe, having developed continuously and without cessation from the fertilization of the egg cell. This young plant then drops into the water where, like the young mangrove, it floats upright—being specially adapted by its structure—and comes to rest on the mud, where it develops at length into the mature plant.
Crinuniy one of the Liliaceae, is another example of continuous development of the embryo without a resting stage. Thus it is not possible, in any of these particular cases, to store the seeds, as can be done with those of the majority of flowering plants.
Of the two main problems which have to be solved by the developing embryo in the seed, the first is its method of escape from its protective seed-coat and the second, the provision of its food supply during the early stages of its development.
With regard to the method of egress or escape, 1 will deal with certain remarkable Dicotyledons later, but for the moment 1 may remind you of the contrivances evolved in the palms generally and also in the genus Megarhiza't^ {Cucurbitaceae). In these cases the embryo is enclosed in a sheath or germ tube, the lower portion of the cotyledon, and this germ-tube, on germination, pushes through the micropyle and carries with it the young embryo which is thus *
* Kernel and Oliver. The Nafural History o f Plants, I. p. 602, figs. 142, 143 ; Guppy, H. B. Obscrv'itions o f a N aturalist in the Pacific, II. Plant-dispersal, p. 440.
t Boodle, L. A. and Hill, A . W . Typhonodorum Lindleyanum, the Development of the Embryo and Germination of the Seed, Ann. Bof. Vol. XLIII, 437, (1929).
X Hill, A. W . Studies in seed germination : the genus Marah (Megarhiza), Cucur
bitaceae, Ann. Bof. Vol. X X X . p. 216. (1916).
transported from the interior of the seed into the soil. The germ- tube or cotyledonary sheath then bends down and carries the contained embryo to the proper depth in the soil, the energy being provided by the endosperm which is being absorbed by the apex of the cotyledon within the seed and passed down the wall of the sheath to the young embryo lying outside the seed in the soil.^f In due course the embryo develops its first leaf, which pushes through the wall of the cotyledonary sheath and emerges into the air and performs the functions of an assimilating organ. The young plant then becomes independent and continues its development in a normal manner. In some cases the young seedling attains its independence in a few weeks, but in the case of the Double Coconut {Lodoicea), the large seed is retained for a long time and the young palm continues to draw nourishment, by means of its cotyledon, from the endosperm stored in the seed for several years.
There are, however, certain anomalous Dicotyledons to which 1 wish particularly to draw your attention, which are peculiar in having apparently only one seed leaf instead of the normal two cotyledons. These include certain bulbous and rhizomatous species of Peperomia from the High Andes of Bolivia and Peru and the mountains of Central America, the genus Cyclamen {Primulaceae) Ranunculus Ficaria, Bunium {Umbelliferae), Allionia, Abronia, TrapUy and several genera of the family Gesneriaceae including Streptocarpus, Chiritay T)idy mo carpus y SaintpauliOy MonophyllaeUy etc. These ano
malous types of seedling are nearly always associated with some peculiarity in the morphological structure of the adult plant, especially the adoption of the “bulbous** habit.
In the case of the Peperomias,t the seedlings possess only a single green cotyledon and the tiny seedling looks at first sight exactly like that of a typical Monocotyledon, with the seed remaining below in the ground and the green assimilating cotyledon in the air.
* Kerner & Oliver, l.c. p. 607, fig, 144 (7-10) Phoenix daclylifera,
I Hill, A. W . The morphology of seedling structure of the geophilous species of P eperomia, together with some views on the origin of Monocotyledons, Ann. BoL Vol. XX.
p. 395 (1906).
I A C S
nil mil nil
9293
Explanation of Text-figures of various seedlings of Peperomia in median longitudinal section.
Pt = w all round the seed (pericarp and testa) ; T = testa ; Pm = perisperm ; E = endos
perm ; C = cotyledons ; C i = absorbent, Co = aerial cotyledon ; P = plumule ; Hyp = hypocotyl ; H = cavity in the endosperm left by the withdrawal of one or both cotyledons.
Figs. 1 and 2. Peperomia pellucida (after Johnson).
1. Commencement of germination of the dicotyledonous embryo with its sheathing endosperm.
2. The two aerial cotyledons free from the seed, which is empty and shrivelled.
Figs. 3 and 4. P. peruviana.
3. Slightly diagrammatic, showing the positions of the two cotyledons within the seed.
4. One cotyledon ( C j) remains within the seed, the other becomes an assimilating organ (C j) ; in both cases the laminae are slightly peltate ; a large cavity is left in the endosperm on the withdrawal of the aerial cotyledon.
Figs. 5 and 6. P. parvifolia, diagrammatic, since part only of a seedling has been found.
5. The more complete specialization of the absorbent cotyledon ( C j) to form a club- shaped organ, and the rudimentary aerial cotyledon (C2).
6. Older seedling, showing the further development of the assimilating cotyledon (C j), which is of very little value as an absorbent organ, and the commencement of the hypocotyledonary swelling. Only a very small cavity is left in the endosperm on the w ith
drawal of the aerial cotyledon.
Figs. 7-9, a typical Monocotyledon.
7. The seed w ith the young embryo. The “first leaf” or second cotyledon is very rudimentary and is covered over by the sheath of the absorbent cotyledon. It is carried out of the seed together with the plumule and the radicle.
8. The further development of the rudimentary aerial cotyledon from the base of the sheath of the absorbent organ ( C o ) .
9. The aerial cotyledon (C2) has burst through the sheath of the absorbent cotyledon ( C j) and is pushing up into the air with a sharply curved petiole. (From 'Annals o f Botany', Vol. XX, p. 420).
On closer examination, however, it is found there are actually two cotyledons present, each having a different function ; one emerges from the seed and becomes a green assimilating leaf, while the other r^ever leaves the seed but functions wholly as an absorbent organ, transporting the nutritive material stored in the endosperm to the developing seedling. This peculiar geophilous group of the genus T^eperomia thus exhibits a very special and unique type of germina
tion, which may be termed pseudo-monocotyledonous, unknown elsewhere among the flowering plants. Cyclamen^ also may be classed as a pseudo-monocotyledon, but here the anomaly is on somewhat different lines, for only one cotyledon normally develops and, after first serving as an absorbent organ, it then emerges into the air and persists for a long time as the first green leaf of the young
uCl u
L2
Cydlaynen neapolitanum. Fig. 1. A germinating seed, showing the cotyledon petiole, C i, and the rudiment of the second cotyledon, C2. Fig. 2. The cotyledonary lamina with the seed have been removed, and the second cotyledon, C2, is developing. The petiole of the normal cotyledon. C l is beginning to wither. Fig. 3. The first cotyledon, has been unable to free its lamina from the seed-coat, and the second cotyledon, C2 has developed and expanded its lamina. G. persicum. Fig. 4. The petiole of the normel cotyledon with the lamina removed. A new lamina, L2 has developed from the edge of the groove of the petiole near the cut surface. Back and front views. *
* Hill, A , W . Studies in seed germination : experiments with Cyclamen, Ann. Bot.
V ol. X X X IV . p. 417 (1920).
plant, and by its activity builds up the young corm or “bulb” which is a characteristic of the genus.
Cyc/amen, however, like Peperomia, does possess a second cotyledon, but only in a rudimentary form and it never develops into a leaf unless the main cotyledon suffers some serious injury. By experimenting in amputating the lamina of the normally developing
“first” cotyledon, the second rudimentary cotyledon can be induced to develop and produce a petiole and lamina very similar to that of the first cotyledon. Moreover, it may be noted, the first cotyledon has certain peculiar properties, for when the lamina is removed a new lamina can be produced from the flanges of the inner side of the petiole, just below the point of amputation, and this new lamina consists of two flanges at right angles to the position of the original cotyledonary lamina, a process which can again be repeated lower
Typical seedling of Ranunculus F iearia showing the bilobed cotyledon C i and first foliage leaf Fj. The part marked by a bracket was embedded for section cutting.
down the petiole if this first secondary lamina be removed. It has been found that the second cotyledon, when induced to develop, possesses meristematic activity similar to that of the normal cotyledon, thus affording further proof that the rudimentary lump of tissue, which develops as the result of amputation, is actually the second cotyledon •, for it is only the cotyledons which possess this power of regenerating a new lamina from the petiole, the plumular leaves which subsequently arise being quite unable to do so.
Cyclamen is thus an example of the loss of function of one of the two cotyledons in contrast to Peperomia, where the two cotyledons have assumed different functions.
In Ranunculus Ficaria there is again apparently a- single cotyledon present, and Bunium and one or two other aberrant bulbous Umbelliferae may be classed with it. In R, Ficaria, as Metcalfe^J=
has recently shown, it is not a case of the fusion of the two cotyledons into one, as the late Miss Sargant attempted to prove,'t’ but the total supression of one of the two cotyledons. R. Ficaria is thus truly monocotylous by abortion. Pinguicula vulgaris, where only one coty
ledon can be found, is probably a similar case of complete suppression of the second cotyledon.
The three species of Abronia {Nyctaginaceae), which were considered to come amongst the monocotylous examples, must also be omitted, for it is now generally agreed that both cotyledons are present, one developing later than the other. In the case of the closely-allied genus Allionia, both cotyledons are present in the embryo, but one of them is only about half the size of the other.
Trapa natanst {Onagraceae) is another abnormal Dicotyledon ; for the seedlings start life with two equal-sized cotyledons, but only one of them grows on, while the other remains quite small. The *
* Metcalfe, C. R. A n interpretation of the morphology of the single cotyledon of Ranunculus Ficaria based on embryology and seedling anatomy. Ann. Bot. Vol. L. p. 103 (1936).
t Sargant, E. A. Theory of the origin of monocotyledons, founded on the structure of their seedlings. Ann. Bot. Vol. XVII. p. 1 (1903).
+ Kerner and Oliver. The Natural History of Plants, I. pp. 607 & 609, fig. 144 (3 & 4).
larger one grows on and pushes the young plant out of the seed and also acts as an absorbent organ within the seed.
Turning now to the family Gesneriaceae it is interesting to find that the genera Stfeptocarpus Didymocarpus and Chiritay in particular, exhibit a peculiar and somewhat anomalous type of germination. The young seedlings for the first few days of their existence are quite normal Dicotyledons, with two equal-sized cotyledons. About the third day, however, it will be noticed that one of the two cotyledons is increasing in size, while the other remains stationary and ceases to grow, and eventually this smaller one turns yellow and falls off, leaving the seedling plant with only one greatly enlarging seed leaf or cotyledon. Further it will be noticed that the cotyledon itself does not really grow, but the enlarging lamina is developing as
Streptocarpus. Figs. 1-5. Figs. 1 and 2. Streptocarpus Galpinii, seedlings in surface and side view ; the densely hairy adventitious lamina of the persistent “cotyledon” carries the glabrous original cotyledon at its apex ; note the minute glabrous second cotyledon (C..) (x 3). Fig.' 3. Streptocarpus sp., a seedling showing the development of an adventitious lamina to the second cotyledon (Co), the actual cotyledon remaining a distinct entity ( x 3).
Fig. 4. The same, the second cotyledon in surface view ( x 3). Cf. Plate V. Figs. 10, 11.
in. Ann. Bot. new series, II. Fig. 5. The same, a seedling with both cotyledons developing ( !)• (From 'Annals o f Botany', New Series, Vol. II, p. 129).
the result of the meristematic activity of the tissue at the base of the cotyledon where it joins the hypocotyl, and the actual cotyledon is
tamed as a distinct entity at the tip of the enlarging lamina. Here, again, the seedlings have become monocotylous by abortion.
In several of the S. African species of Streptocarpus and in one or two species of the Asiatic genus Chirita, this enlarged cotyledon is the only green leaf of the adult plant and the flowers are borne in acropetal succession along the midrib. There are, however, several African and Malayan species of Streptocarpus and most of the species of Chirita from Siam, Malaya, India and China, where the plumule, which is arrested in the monophyllous species, develops normally and produces a tall stem with pairs of opposite leaves and flowers in the upper leaf axils ; or, in some species of Chirita, the flowers are borne on the midrib of the upper sessile leaves exactly as in the mono-
Dfdymocarpus Figs. 11-16. Fig. 11. D. pimcticulatus, a young seedling showing the unequal cotyledons at the same level ( x 6). Fig. 12. The same, an older stage, the persistent cotyledon ( C, ) has been carried up by the development of the plumule ( x 6). Fig. 13. D.
Mortoni a seedling from above showing the small glabrous second cotyle ’on and the large hairy persistent one ( x 9). Figs. 14 and 15. The same, later staged showing the development of a petiole to the persistent “cotyledon” ( x 9). Fig. 16. 1). platypus, a. well-advanced seed
ling showing the persistent cotyledon ( C, ) at a higher level than the small one (C2) ( X 4).
(From "Annals of Botany' New Series Vol. II. P. 134).
phyllous species. It is, however, a remarkable fact that. in these herbaceous, caulescent species, the seedling structure is identical with that of the monophyllous ones, for, though both cotyledons are present in the early days of the seedling’s existence, only one of them develops and the other ceases to grow and decays exactly as happens with the monophyllous species.
Chirita lavandulacea Stapf. Fig. 20. Seedling in young stage showing the two dissi
milar cotyledons. Fig. 21. A more advanced seedling ; the enlarged cotyledon ( Ci ) has developed a petiole (C._, the smaller cotyledon, P. scar of the removed plumule). Fig. 22.
A still later stage, the enlarged “cotyledon” being exactly similar to a plumular leaf. Fig. 23, Part of hypocotyl and plumular stem of a young plant showing buds in the axil of the persis
tent cotyledon and none in that of the undeveloped one. (Al l x 1) (from \Annals of Botany', New Series, Vol. II, p. 139).
•A further peculiarity of these caulescent species may also be noted, since an axillary bud (or sometimes two or three), develops in the axil of the persistent cotyledon, but not in the axil of the aborted one, with the result that the adult caulescent plants are always
“lopsided”, not only in having one larger, petiolate, unpaired leaf at the base of the stem—the persistent cotyledon—but also in having a strong axillary shoot on one side only, which sometimes may be almost as stout as the main axis of the plant.=?^
How can we account for this peculiar state of affairs ? Only, 1
think, by assuming that the monophyllous character' exhibited by Streptocarpus Dunniiy S. Wendlandii, etc., is the primitive condition of affairs. That • is to say, that at some stage in the evolution of the genus, since only one leaf was found necessary in the life history of the plant and that this was provided for by the enlargement of one of the cotyledonary leaves, the function of the second cotyledon was lost and it therefore aborted. Later, conditions arose which led to the development of the arrested, plumular shoot, but the function of the second cotyledon having been lost its suppression was continued and it has never been regained. This case affords a good example, on the botanical side, of Meyrick’s L aw ,t enunciated for the Lepidoptera, “a lost organ cannot be regained”.
This hypothesis receives striking confirmation in one or two species of Chirita, notably C. capitis from Siam. In this species seedlings grown on a vertical wall remain monophyllous throughout their life and in their morphological structure are identical with the monophyllous species of Streptocarpus. however, seeds ger
minate on good soil at the foot of such a wall, a tall, herbaceous plant with a well-developed plumular shoot is produced, similar to other caulescent species of Streptocarpus and C/i/n7a, thus showing the influence of conditions on the morphology of the plant.$ Other species of Chirita, Did^mocarpuSy etc., (such as C. bifolia D. Don, C. *
* Hill, A . W ., Ann. Bot. New Series Vol. II, Plate III.
t E. Meyrick, Hand book of British Lepidoptera, 1895, p. 10.
X Hill, A . W ., Ann. Bot. New Series V ol. II, Plate IV.
monophylla C. B. Clarke, C. hamosa R. Br. var. unifolia C. B. Clarke, and C. pumila D. Don), may be cited in confirmation of this hypothe
sis. It is unnecessary to enter into details as to the behaviour of other monophyllous genera of Gesneriaceae such as MonophyllaeOt Moultonioj etc., as they merely afford confirmatory evidence of the facts already described. It is, however, a matter of speculative interest to consider how it may have come about that plants so widely scat:
tered from South and Central Africa to Malaya, Borneo, the Hima
layas, China, the Pyrenees {Ramondia) and America {Klugia) should have evolved the peculiar habit of retaining only one of their two cotyledons.
Very rarely seedlings of Streplocarpus, but more especially among the cultivated forms, develop both their cotyledons in the
typical way, but it is very difficult to induce the second cotyledon to grow in normal seedlings. This has been effected, however, in a few cases in Streptocarpus and Chirita, by repeatedly amputating the enlarging cotyledon at intervals of two or three days. In such cases it is even more evident that the cotyledon itself does not enlarge, but that the enlarged growth is entirely due to meristematic activity at its base, for the lamina of the second cotyledon can then be seen to be carried as a small glabrous entity at the apex of the broad hairy lamina.
The extent of the activity of the meristem at the base of the cotyledons in these Gesneriaceae is well seen in the large single leaves of Monophy^llaea and Moulionia^ and also in some species of Streptocarpus^ which may be as much as 30 inches long and 22 inches wide. These genera, therefore, which are of so much interest on account of their peculiar seedling structure in retaining only one of their two cotyledons, are also remarkable in the “adventitious* **
production of a large lamina—together with a petiole in Chirita—by meristematic activity at the base of the persistent cotyledon.
* Balfour and Smith, Moultonia, a new genus of Gesneriaceae from Borneo, Notes Roy. Bot. Hard. Edinburgh, 1915, Vol. VIII, p. 349.
Cotyledons in general usually function for only a short time and fg^ll off soon after the plumular leaves have developed. This is particularly the case with assimilating epigeal cotyledons. Hypogeal cotyledons, however, which may either be stored with nutrient materials or be the agents for absorbing food supplies from the endosperm are usually somewhat longerdived and will retain their vitality until all the food supplies contained in them or in the endosperm have been exhausted.
Possibly the Monocotyledons, and especially the palms, supply the best examples of longevity of the cotyledon, and the Double Coconut {Lodoicea), to which attention was drawn earlier, is no doubt the outstanding example. The cotyledon in this case may attain the age of ten or more years, since it continues to function and act as an absorbent organ, supplying food to the growing palm, until all the food supplies in the great endospermic store have been consumed.
^.ECTURE III.
Seeds protected by Stony Endocarps
The adequate protection of the seed with its contained embryo, is, as I pointed out in my previous lecture, the chief concern of the plant and various devices have been evolved in order to achievf this object.
In some cases the seed only is involved and the testa and tegmen, the two seed coverings, may be adequate for the purpose and protect the embryo so that it remains in a viable condition for a considerable time. This may be seen particularly well in the family Leguminosae, where the leathery testas of the seeds are sufficiently impervious to afford adequate protection for the dormant embryo and allow it to retain its vitality for very many years. How the spark of life in the embryo can be maintained for so long a time in a dormant condition does not concern us here, but it may certainly be regarded as one of the mysteries exhibited by the vegetable kingdom.
How long vitality may last is not definitely known, but as 1 have mentioned, after some 90 years certain seeds have been found still capable of germination* and, if the account of the Japanese Nelumbium seed be correct, then we may accept the fact that these seeds have retained their vitality after being buried for some 400 years, t
Very possibly seeds of the common Charlock (5fnapis arvensis L.) should be given the pride of place in the matter of longevity^. It is well known that if land long laid down to pasture is ploughed up, a large crop of Charlock will appear the following year, due to the germination of seed buried deep in the ground when the land was laid down to grass and now exposed to the air by the plough. A very striking example of the persistence of Charlock seed in the soil
* Turner, J. H. “The Vitality of Seeds”, Kew Bulletin 1933, pp. 257-269.
t Ewart, A. J. “On the longevity of Seeds” Proc. Roy. Soc. Victoria, vol. XXI (N. S.). pp. 1-210 (1908). Turner, l.c. p. 261.
X Hill, A. W . “The flora of the Somme Battlefield” Kew Bulletin 1917, pp. 297-300, and Turner l.c. p. 258.
was aflorded during the Great War. The Somme battlefield which was so heavily shelled, was ablaze the following year with millions of poppies {Papaver) and produced an effect of wonderful beauty.
These had all developed from seeds long buried, but more remarkable than the poppies was the occurrence of Charlock in the spots where graves had been dug in the battlefield for temporary internments.
In such places the chalky soil had been more deeply dug and Char
lock seed had been brought to the surface where it was able to germinate. How long this seed may have been buried under suitable anaerobic conditions it is impossible to estimate, but it may well be that seed of this Brassica would be found to retain its vitality under suitable conditions longer than any other seeds of which we possess authentic records. Whatever may be the verdict as to the longevity of Charlock seeds, I cannot refrain from mentioning the unforgetable sight of the great sea of scarlet-flowering poppies with here and there, the bright-yellow patches of Charlock marking the spot where a
soldier had been laid to rest.
But to return to my subject, “The protection of the Seed” :—
the embryo within the seed may be compared to a prisoner carefully shut up in his cell, and we may consider first the nature of the prison and secondly the way in which the prisoner is able to effect his escape—that is, the mode of germination.
In the majority of cases where the seed only is concerned the methods of germination are so well-known that it is unnecessary to
I.
enter into any details. It is' to those cases where the seed is enclosed, in addition to its seed coats, by some persistent portion of the fruit-wall that 1 wish to draw your attention.
The fruit-wall, as is well-known, usually consists of three layers : the outer one, the exocarp ; the middle layer or mesocarp, which is usually fleshy and frequently edible, either by birds, animals or man ; and the inner layer, the endocarp, which is usually of a woody or stony nature, and constitutes the “stone” of the fruit.
The peach or the plum (Prunus) and the walnut (Juglans) are good example of the simple type of fruit containing a single
