Madras Journal of Literature and Science/New Series 1/Volume 2/On the Relationship existing between the Animal and Plant
Between the animal and plant of the higher orders there is such an apparent difference of conformation, such a contrariety of habits, that the mere casual observer will fail to recognise those secret links, by which nature binds all her works into one harmonious whole. In whatever direction however the contemplations of the naturalist tend, from race to race or from kingdom to kingdom, he discovers no rude gaps but a beautiful unison, for nihil per saltum is one of the great laws of creation. If we descend the scale of nature, reaching the extreme boundaries, the lowest forms, of the animal and vegetable kingdoms, we find members of these great divisions approximating so closely, that it becomes a matter of difficulty to draw any line of demarcation. The limits here are also hazy, because so far beyond the ken of unaided vision, and although the microscope has unveiled nature's secrets, disclosing a new world grand in the plenitude of its minutiæ, still its scientific eye is finite failing at times to decide which is the animal, and which the plant. It has been said that "stones grow, vegetables grow and live, and animals grow, live and feel," but this axiom is not sufficiently extensive in the terms of its definition. Thus plants in some instances seem capable of distinguishing between light and darkness, for many only open their leaves or flowers to the sunshine, while others the plantæ tristes, the watchmen of the flower garden, only spread abroad their beauties to the night. Other plants exhibit a certain amount of irritability, or sensitive qualities, under mechanical or chemical stimuli. The Drosera and Dionæa woo the unwary fly to its destruction shutting it up in deadly folds, while the Mimosa sensitiva and a few others will shriek from the most delicate touch, and may be laid asleep, during any severe operation of the gardener, under the influence of opium or Chloroform. If on the other hand we assume as the characteristic of the animal, its capability of changing its position, we still find similar properties in the plant; for vegetable organisms are in some instances capable of changing their position and performing other movements. Thus the Zoospores of Cryptogamic plants are locomotive, and the Desmodium gyrans is possessed with a restless activity, its lateral leaflets dancing a perpetual measure to the music of the air. As we compare then these indications of sensibility, and these locomotive powers in the vegetable with the humbler endowments of such an animal as the sponge, which remains through life chained to one little spot of rock, giving out no indications of sensibility, we must at once be struck with the difficulties attending a true distinction, and the intimate relation that exists between the two kingdoms in question. True, we cannot instance the automatic performances of the vegetable as identical with the similar endowments of animal life, but still they indicate a sympathy, a harmony existing between the two organizations, and show us how closely the great principles of animal and vegetable life converge. Indeed, as they approach the common centre, the little cell that is the habitation of both, it is perhaps impossible to say, here begins animal and there vegetable life.[1] These, here in their infancy, are subtle essences far beyond our conception, and the naturalist, as he gathers this new world together on the field of his microscope, can only judge and name, after long and patient study of conformation and habits.
Thus far we have dealt in generalities, let us now therefore examine move closely the consanguinity of the two kingdoms, beginning Nvith the birth of the members of both in a simple cell, and then con- sidering what important parts cellular structures play throughout all the economy of their future life. Buffon on beholding the smallest animal of the existence of which we are aware, the little monad that swarms in stagnant water, ynagined that all vegetable and animals were built up of these minute cells. True to its unchanging philosophy, which laughs at every new truth, the world sneered at Buffon's impro- bcible idea ; but we know n*w that the sage naturalist saw truth in his dreams. Tl^e smallest of the Infusoria, the most minute Cryp- togam are but simple cells living an independent isolated life, and every living structure however complex, however strange, has had a cellular origin, and is indebted for its growth and maintenance to the modification and development of cells.[2] The cell consists of an enveloping membrane or cell wall, that encloses a peculiar fluid and nucleus or cell-germ. True we find numerous examples of ceils that do not exhibit even the trace of a nucleus, but from these it may either have been removed by absorption, or it may be destin- ed to appear at some future era of their existence. The modes of Cylogenesis are various, but nearly all agree in being common to the animal and vegetable. To the older Physiologists the subject of reproduction was fertile in speculation and romance, and it was only wh^n the theory of cells and their development became known, that we were able to read its history in the earlier and more myste- rious stages. In the higher animals and plants, the process is com- plicated in accordance with the general plan of organization, but as we approach the simple infusorial animal or cryptogamic plant, w^e can with facility explore the plan of nature's grand secret. Here new generations originate in accordance with the laws of Cytoge- nesis, the nucleus of the parent preparing a future race, or some of the other systems obtaining by which the old cell begets the new.
Remembering then that Cytogenesis is in all cases the necessary part of the process of reproduction, if from the generation of the lower species we proceed upwards to the more perfect animal or plant, we shall find that any complication of plan is merely supplementary for the nartare and dcTelopmen: of a superior embryo. I: 15 unrcfssary to compare the Tarious structuTes that are met v:v.z i- : kingdoms, as the results of the transformation of Crll5. I ; find tubnlar tissues formed by the coaleseence
- it-.s. sclerous tissaes where the cells hare been solidified by internal deposit, iT-:=:t. " A : iian Mollosca a considerable quantity of
ce. ..^:;; : 5 per of plants. Indeed one observer relates, thi: ^ . z rcted by chemical reagents in the corpora r. brain; and if we can therefore credit V . . .:l ..zaber headed" will after all have a foundation in truth.
We now come to consider some ©f the functions of organic life, premising that in all organs where these vital operations are car- ried on, we find a true cellular structure retained. Beginning with absorption and assimilation, we fiad these processes varying, ac- cording to the rank of the animal or plant, in the respective kingdoms, but still agreeing in the constant cellular agency. Amongst individuals of humble status, the nutritious matter is at once received through the cell wall by the process of endesmose, to be elaborated and applied in the cavity of the cell to the various wants of the structure. This of all methods is the most simple, and a key to the plans of absorption and assimilation in the higher di- -visions, inasmuch as any apparatus more intricate is merely super- added for the production of a more elaborate nutritious fluid, and its transfer to distant parts of the organism. In the Yertebnta absorption and assimilation obtain in their most perfect state, as we And in this group a distinct tubular system, solely concerned in the manufacture and translation of the chyle or alimentary fluid. Between this and the simple endesmose and assimilation of the ani- malcule, there are many intervening gradations of process, and as an example of an animal occupying an intermediate position be- tween the two extremes, we shall briefly contemplate the internal economy of an Annelide, the Himdo medUinali*. In this creature, nearly the whole of the visceral cavity is filled by the stomach, which consists of an elongated tube with a number of lateral sacs. Over these cscal appendages is spread a delicate net-work of the terminal branches of the circulatory system, destined to receive by endesmose the elements of nutrition, which thus pass in their crude state into the general circulation, where they are elaborated and fitted for their future destiny. In the vertebrate animal, the lacteals already referred to terminate by looped extremities amongst a number of cells and nuclei; and during the passage of chyme along the intestine these nuclei become developed into cells, and the cells are busy at work selecting, absorbing and elaborating, and then yielding up their contents to the loops of the lacteals. In plants the root is the great organ of absorption, whether suspended in air, floating in water or buried in the earth. The root consists of a cellular epidermis, and internal structure of vascular bundles and cells. Here then cells are still the great organs of absorption, and if we trace the sap upwards through the alburnum and leaves, and its return through the lactiferous vessels and cells of the bark, we shall find them not less active and essential in the process of assimilation. If we now review the function of respiration in the animal and plant, we shall find that although by this process the animal eliminates carbon and consumes oxygen, while the plant fixes the former and gives off the latter, being thus so far opposed in object, they nevertheless agree inasmuch as respiration is carried on in both kingdoms, by means of organs of a cellular structure. In both too the ultimate objects of the function are the alteration and refinement of the circulating or nutritious fluid, the blood in the one and the sap in the other being fitted for the production of new or repair of old tissues, and for keeping up a supply of the various secretions. Respiration is therefore a depuratory process, and perhaps the least vital of any of the functions of organic life, many of the changes it effects being merely the results of a chemical action. We come now to speak of secretion, which is carried on by means of certain cellular organs called glands. These appropriate each a definite nature of material from the circulating fluid, as it passes along fertilized by the results of absorption and assimilation. Besides their nutritious elements however, the blood and sap contain unorganizable substances the effete products of tear and wear, which are separated to be excreted by glands differing in no important particulars from those already mentioned. The individual cells concerned in the manufacture of the various secretions, as they disclose no appreciable disparity in structure to account for the dissimilarity of their products, must therefore possess some special endowment or quality, whereby they are enabled to make a selection of material. The mode in which the gland as a whole is constructed can have no direct influence in this respect, for secretions are vicarious and the same gland assumes different forms in different grades of the animal kingdom. We have not space to compare the secretions of the two kingdoms, and would merely insist on the similarity of secreting structures in both, and the mysterious faculty that these possess of selecting certain substances, and only these during health, from the circulating fluid.
Thus through all the functions of organic life, there exists between the animal and plant a wonderful consanguinity. In both we find a variety of processes instituted with a view to the same results, and performed by means of structures identical in the plan of their conformation. There are still however other relations, equally strange, existing between the two kingdoms; and these are perhaps more directly practical in their bearings than those already noticed. The great Creator of the universe, has established a fixed Geographical distribution of the varieties of the animal and plant, that cannot be departed from without incurring the risk of disease or even death. The Esquimaux enjoys perfect health, living in his snow-hut and feeding upon raw flesh, the supply of whi<;h is far from regular or abundant; a mode of life that would, to say the least of it, be dangerous to any native of a temperate climate, and death to any member of an intertropical race. On the same inhospitable shores of the frigid zone, we find a scanty flora of Saxifragacese, Salices and Cochleariae, not one of which has ever been removed to a milder climate with impunity. Still more impossible would it be to transplant and to adorn with our Magnolias, Camellieae or Palmae, the ice-bound coasts of Labrador or Greenland; or to exchange for the Lion and Tiger of the one region, the fiercer and more powerful White Bear of the other.
Early in the summer of 1852, a dog and bitch only a few months old were picked up by me on the shores of Melville Bay in about 75° N. Latitude, Both were in good health so long as we remained in high latitudes, but on the homeward voyage as we approached the Orkney Islands, in the month of cold November, both animals became sick, suffering from fits, The dog died of congestion of the brain, just as we sighted land, and towards the close of the following spring the bitch, which was then in the Highlands of Scotland, died I believe from the same cause. We have little reason to doubt that in both these cases, elevation of temperature was the exciting cause of disease. Of several varieties of hardy garden seeds imported from England in tin cases, and sown in a garden soil of fair quality in Kirkee this season, only a very few specimens have lived to come above ground; and yet the seeds looked fresh and healthy enough. In several colonies to which seeds, such as corn and barley, have been sent from Europe, even these sturdy plants suffered from the change of climate, and it was only after the careful culture of a few years that they began to yield an abundant return. On the other hand the agriculturist knows well the advantage of having seed from a limited distance, where there is not any considerable difference in climate involved in the change. Those at all conversant with a pastoral life also know the change in height and appearance that takes place in the Shetland breed of ponies, when transported young from their native shores to the south of Scotland or to England. Such a change of pasture and climate has also no little influence on the breeds of cattle and sheep.
Indeed it is an article of our medical creed, that local climate, and quality of soil exercise an important influence over animal and vegetable life. Amid the dank exuberant vegetation of the jungle, diseases exhibiting great vascular excitement are but too common; amid the smoke-begrimed, tainted atmosphere of the great city what an enervated sickly debased race grow up, and who that has seen in the same sphere a few plants tortured into existence, can say that they looked healthy? The heather is a sturdier plant than the rose or the shamrock, and in general hill tribes are endowed with a physical energy superior to that of their Neighbours of the plains. On a poor miserable soil, with scarce vegetation to cover its nakedness, we shall ever find a wretched and thinly scattered population. Looking backwards to the Geological eras of this venerable earth, we also find most wonderful relations, as to rank in their respective kingdoms, existing between the classes of animals and vegetables living at the same time on the stage of the world. Thus during the Palaeozoic division of fossiliferous history, amid awful forests, pestiferous jungle, and impenetrable underwood consisting of Monocotyledons, Gymnogens, Acrogens and Thallogens, there lived molluscs and a few reptiles, while the waters of the same period were occupied by corals and crustaceans, all animals of low type. Advancing to the next or middle great division, we find specimens of the classes enumerated as characteristic of the previous period, only modified in accordance with other features of that creation. In addition to these however, we have gigantic reptiles and birds, a few mammals and some dicotyledonous plants. Then comes the tertiary period, when the dicotyledon is king of the forest, when mammals of immense proportions are predominant, and reptiles are dwarfed into something like their present size. Thus throughout the two kingdoms we have a contemporaneous progression from the lower to the higher forms, as the earth is changed from an impracticable to the present world with all its beauteous creations, of which man is lord. We find no traces of his footsteps however, in the Palaeozoic or any other formation, until the earth has been made a fit and pleasant habitation for him and his seed for ever. Neither have we a plant of the higher orders, living together with animals or vegetable forms of low caste, during an early fossiliferous era. Tne sun did not then shine with his present benignity, not a bird looked down on its shadow in those dreary waters teeming with monsters, never did its notes sing of verdant plains, of pleasant groves, of fertile valley and bounteous river, but the discordant cries of fearful forms, the weak in their death agony, the strong rejoicing in their might, startled the echoes amid forests of fabulous extent and trees of eccentric appearance. In each and all of these periods of Geological history, we find certain classes of animals co-existing with consonant grades of vegetable productions. We find not a single departure from this rule, for throughout all the works of the great Creator there is a constant harmony.
"In reason's ear they all rejoice And utter forth a glorious voice, The hand that made us is divine!"
- ↑ This animal and vegetable affinity is very amusingly discussed at p. 448 of the April No. of the Dublin University Magazine 1957.—Ed.
- ↑ * Th« exceptions t-^ this general rul$ do not demand special notice.