The plant, an illustration of the organic life of the animal

Front matter

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Preface

Tur two volumes on Cryptogamous and Phanerogamous plants already published by the author, were written with an “especial reference to the wants of medical students and physicians.” Botany has not yet obtained that position to which it is deservedly entitled, as a preparatory study to the organography and physiology of animals. It is still excluded from the most important medical schools; and this state of things will continue despite of all the efforts of botanists, so long as the plant is regarded as if it were isolated from the rest of organic nature.

The functions of animal life appear to be gradually superadded to those which are strictly vegetative. As we pass from the plant through the coral and sponge to the higher order of animals, bones, blood-vessels and nerves, gradually appear ; the organs of the senses become more perfect, and the motions more complicated, until at length in man, the nervo-muscular system, which has thus been gradually superadded to the vegetative, manifests itself most perfectly in all that, infinite variety of movement and sensation peculiar to rational beings. On the other hand, as we descend from man to animals still lower in the scale of creation, in proportion as the

8 PREFACE.

functions of animal life are suppressed, the vegetative life of the organism gradually predominates, until life becomes wholly vegetative.

Life in plants is therefore limited to the two functions of nutrition and reproduction ; and nutrition and reproduction in animals. are necessarily illustrated by the flowers and forest trees with which the earth is beautified and adorned. Such appears to me to be the way in which organic nature ought to be regarded, such the relative positions of the vegetable and animal creation.

Few, we believe, recognize as they ought to do, the benefits which have already resulted to animal physiology and the science of medicine, from the study of a few humble plants. The great cell-doctrine of physiology, which is now admitied to be the basis of all sound scientific investigations into the phenomena of organized beings, originated in the study of vegetable matter. M. Mirbel, in a most admirable memoir on the development of Marchantia polymorpha, a little acotyledonous plant belonging to the family of the Hepatice, was the first to show the cellular origin of every other form of vegetable tissue. He proved that the fibre cells of plants are only attenuated utricles, and that the different varieties of . vasiform tissue aad ducts, by which the interior of the plant is aerated, originate in.a row of utricles ; these gradually elongate, and the various secondary deposits characteristic of the different forms of spiral vessels, appear on their internal surface; the septa or partition walls between the several cellules are then absorbed, and the transformation of the utricles into vessels is completed. These observations were confirmed by the researches of Schleiden and other distinguished botanists,

PREFACE. 9 and thus a flood of light was thrown on the organization of plants.

_ But how do the cells of plants and animals originate? How do they multiply and extend themselves so as to produce the growth or enlargement of the organs? These are difficult but interesting questions, and botanical researches have enabled us to reply to them satisfactorily.

A German naturalist, Mohl, selected for observation one of , the fresh water algae, which had been previously figured and described as Conferva glomerata. This simple, thread-like plant was placed beneath the microscope, and the development of the row of utricles of which its entire organization consists, watched. Very soon, Mohl observed that the interior face of the cavity of one of the utricles presented towards its middle part a fold, which increased almost imperceptibly until it ended by forming a complete wall dividing the cavity of the utricle into two parts. Hach of these then dilated itself into a new utricle. Thus in the place of one cell there were two cells, which again divided in the same way, and so on. ‘It is in this way that a single cell gives rise to a row of connected cells, when the division takes place in one direction, and to a plane or solid mass when it takes place in two or more directions. There are other modes of increase which we shall notice in the ensuing pages; suffice it for the present to say, that their discovery originated in the investigation of cryptogamous plants of extreme simplicity of organization.

" Up to this period it was believed by the most eminent physiologists, that animal and vegetable tissues differed widely in their development, and that cells existed only in plants. Such was the condition of things in 1838, when Schwann, taking up

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the beautiful investigations that Schleiden had just published upon the structure and growth of vegetable cells, came to the conclusion that animal tissue consisted equally of cells, and that whatever may be the character of the tissues, whether they assume the form of muscle, bone, or blood-vessels, all ori- ‘ginate in cells, of which they are but modifications.

Let it, be remembered that these grand discoveries, which have given such an impulse to animal physiology within the last twenty years, originated in botanical investigations. After such fruits have been reaped, the study of the physiology of plants ought to be encouraged. Where would have been our knowledge of the histology of animals, but for the botanical researches of Mohl, Schleiden, Mirbel and other distinguished physiologists? Incalculable, then, has been the amount of good which has resulted to. animal physiology, from the study of the simple and beautiful organization of plants, and in the face of these facts, there is no excuse for the coldness and neglect with which this department of Natural History still continues to be treated. It is not the mere collecting of species, the technical description of their several peculiarities, and their proper classification and arrangement which is here advocated, so much as the study of their vital phenomena and the laws of their development. No extensive acquaintance, either with rare exotics or the choicer native species, is at all necessary for such researches, for these laws may be studied in the commonest weeds growing around our dwellings.”

The views on vegetable respiration in this work are not my own peculiarities ; for they were held by Dr. Gilbert Burnett, an eminent English physician and physiologist. I have also been very favorably impressed with the opinions advanced by

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Dr. Draper, in reference to the exciting causes of the motion of the nutritive fluids in the organism of plants and animals, notwithstanding the attempts which have been made to controvert them. Let it be considered that there is the same successive degrees of attenuation in the conduits of both the sap and blood, resulting from lateral ramifications ; the same beautiful anastomoses amongst the capillaries in which these conduits finally terminate. By these means the nutritive fluids are diffused in all directions, and brought into immediate communication with the cellular tissue of the organs. Let the structure of any exogenous leaf be examined even superficially, without the microscope. The successive attenuations of the fibrous system by lateral ramifications into a network of capillaries, which develop horizontally in a series of closely approximated planes, through the parenchyma of the leaf, show that -the same laws predominate in the distribution and elaboration of fluids in vegetable as in animal matter. At least it is not unphilosophical to infer some analogy, if not absolute identity of function, where there is so manifest a similarity in organic structure. :

T cannot conclude my Preface without acknowledging my obligations to my numerous friends and patrons through whose assistance I have been enabled to produce this volume. ’

In the preparation of Part I. an excellent Chevalier microscope was employed. This instrument was kindly lent me by Dr. Francis Lewis. It gives me pleasure also to mention the services of Dr. Samuel Jackson, Dr. Samuel Lewis, Dr. Francis West, Dr. §. Tucker, the Hon. W. D. Kelly, and Professor Saunders of the French Collegiate Institute, West Philadelphia.

INTRODUCTION.

GENERAL CONSIDERATIONS ON ANIMAL AND VEGETABLE LIFE.

IF we cast a glance at the immense quantity of animals and plants which live on the surface of our globe, we are at first struck with the variety of forms under which they present themselves, with their colors so diversified and sometimes so brilliant, and with the collossal proportions of some, as compared with the diminutiveness of others. But when, after this superficial examination, we study them more attentively ; when we examine with care the structure of each being, we at once see the perfection which exists in its organs, and how well they are adapted to its peculiar habits and mode of life—from the enormous whale, which requires an ocean to swim in, to those minute and myriad forms which find ample room for all their evolutions in a single drop of its waters ; from the lofty tree which has stood for centuries, an ornament in the midst of the landscape, to the lowly flower which attracts us by its beauty and fragrance—all form a collection of objects whose framework is constructed in the most admirable manner, and whose vital manifestations are in the highest degree instructive and interesting.

At first sight, nothing would seem to be more widely

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different from each other, than an animal and a plant. How different is the tree from the bird singing on its branches, or the traveller resting beneath its shade. In the one instance, the organism is immovably fixed to the soil which gave it birth, and has neither the faculty of moving itself, nor that of manifesting pleasure or pain. The hatchet penetrates its tissues, and it falls without any external signs of suffering. But in the other cases, the organic beings are far more highly complicated. They are endowed with the power of moving from place to place, have a will and desires, senses to apprise them of the character and qualities of external bodies, and introduce food into their interior, where a special cavity is provided for its elaboration before it is employed in the nutrition of their organism. Plants have no such special receptacle in their interior. They live, as it were, in the midst of their food. It is furnished to them by nature in a condition fit for assimilation and circulation. They draw it at once from the earth by their roots, and from the atmosphere by their leaves. They therefore possess no special organs for its preparation. It would seem impossible that there could be anything in common between bodies so strikingly dissimilar in their organization and habits.

But if we consider the vital phenomena manifested by animals and plants, we shall very soon see that there is abundant reason-for believing that the difference between these organic productions of nature is not so great as we at first thought.

In the first place, both the animal and plant spring invariably from a being perfectly similar to themselves, to which they adhere during a space of time more or less long, and from which they are finally separated at a determinate epoch, under the form of an egg or a seed, which, under envelopes more or less resisting, encloses a germ. In this germ, all the organs of the adult animal and plant exist in a rudimentary undeveloped condition. Germination, or the act by which these organs disengage themselves from their envelopes, does not increase their number, but only augments their size or modifies their form. The seed contains the plant, and the egg the animal. Thus, they are alike at the commencement of their being. In the second place, the organs of plants and animals,—the root, stem, and leaves of the former, the bones, muscles, and limbs of the latter,—will not grow without a plentiful sup- - ply of food and air. In both instances it is absolutely necessary that the nutritive aliment should be introduced into the interior of the plant or the animal, and be distributed to all the parts of their organization. Now the absorption, circulation, and assimilation of food and air, by animals and plants, is in principle precisely the same process. Abundant proof of this position will be given in the succeeding pages.

Well-marked and obvious distinctions between animals and plants exist only in the more highly organized forms of animal and vegetable life. As we descend to beings of a lower rank in creation, these distinctions become gradually effaced, and we see successively disappear the most important organs of animal life. The organs of the senses become rudimentary, bones, blood vessels, and nerves totally disappear, and in proportion as the powers of animal life are suppressed, those which are truly vegetative gain’ the ascendancy. Thus, the lower orders of the cold-blooded vertebrata, whose bodily temperature is regulated by that of the medium in which they live, become torpid and inactive in common with plants in winter. So also many vertebrated and crustaceous animals change their epidermal appendages. The serpent casts its skin, the bird its feathers, crabs and lobsters their claws, just as the leaves and bark fall from the branches and stems of trees. Moreover, the exercise of the reproductive function which in man is not limited to any particular time, is periodical in inferior animals, precisely as plants flower and fruit at certain séasons of the year. At length, in the lowest orders of the animal creation, the animal and plant approach each other so closely that it is hardly possible to draw any line of demarcation between them.

This is the case, for example, with that order of animals which have been very properly called by naturalists, zoophytes, of which the coral and the sponge are familiar examples. These creatures, which show undoubted signs of animality, present also at the same time many striking

Fig. 1.

Fig. 1. Hydra, or polype attached to a piece of stick, with its arms extended in quest of prey. a. The mouth of the animal, surrounded by the tentacula. 6. The tendril-like grasp of an aquatic insect. c. Foot or base of the animal with its suctorial disc. The figure shows also the natural size of the animal.

indications of a vegetable nature. They are not only fixed to the ground like plants, but they have also a plant-like method of growing and propagating.

It is extremely difficult to convey any general idea of a zoophyte, because there is no order of creatures of which the different individuals bear so little resemblance to each other. The organization of the corallines, flustras, sertularias, and other orders of marine zoophytes may, however, be illustrated by that of the Hydra, or common fresh-water polype. These animals, which resemble little pieces of jelly, are found in ponds or slowly running streams, attached to the under surface of the leaves of aquatic plants, or to any floating substance, such as a stick or a straw. They are remarkable for the extreme simplicity of their organization, which consists of nothing but a digestive cavity or stomach, surrounded by a fringe of long thread-like arms or movable tentacula, by means of which the animal procures its food—generally some minute insect or worm, which it seizes with a tendril-like grasp and instantly conveys into its stomach by a contractile effort. The contractility of the tentacula of the Hydra is truly wonderful. When the animal is hungry and in search of prey, the tentacula are extended to a distance of not less ‘than six or seven feet from the mouth of the stomach; but when the digestive cavity is filled with food and the wants of the animal are appeased, they are so contracted as to appear only like tubercles around its entrance.

The different species of corallines, flustras, and sertularias, usually found attached to, or more frequently intermingled with, the sea-weed cast upon our shores, consist of an association of polypes having individually a similar organization to the Hydra, but united together about a common axis of growth like the buds and branches of

Ox a plant. It is interesting to trace the analogies between the members of the animal and vegetable kingdom in the lower orders of animated nature. The sertularian polypes

Fig. 2.

Fig. 2, a. Sertularia or compound polype. 6. Magnified view of a portion of its branches, showing the polype buds.

with their common stalk bearing numerous individuals, have in every instance been produced by continuous growth from a single individual. Here we have a repetition of similar parts precisely as in plants. There can be no mistake as to the vegetative nature of these actions. Each of these associated polypes has an independent vitality of its own, and yet all depend on the general life diffused through the entire community. They individually capture and digest their prey like the Hydra, and yet the products of their individual digestion are applied not only to their own support but to that of the general axis; for the stomachs of the several polypes, communicate with each other by means of a tube which proceeds from the base of each into the common digestive cavity of the stem. Some of these polype buds periodically die and are cast off like the leaves of a tree; whilst others, retaining their vitality, spontaneously detach themselves and evolve into similar fabrics elsewhere. :

It is, however, amongst the alge that vegetable and. animal life appear to be the most completely blended together. It is well known to naturalists that the spores of some of our common fresh water alge, as for instance, conferva glomerata and prolifera rivularis, when first discharged into the water, move about by means of certain ciliary appendages during a certain period of their life. At this stage of development they were observed by Ehrenberg, and were actually figured by him asinfusoria. After awhile, however, their cilie are absorbed, their motions cease, they become attached to some substance in the stream, and develop into plants fixed and immoyable , except from the influence of the current. It would appear from this, that these simple unicellular organisms are animals during the first period of their life and vegetables towards its close.

All organized matter, whether animal or vegetable, consists of cells, and life is only known to us as manifested through ‘their agency. Not only may every animal and plant be traced to a simple cell, but organic nature is evidently only a series of forms which exhibit the successive stages of its development. The animal and plant seem to be blended together in this the primitive form of all organized being. It is here that the last signs of animality disappear, after which, life becomes wholly vegetative.

It is not then among vegetables and animals the most highly organized, that we find the most striking analogies between the animal and vegetable kingdoms, but it is those which possess the greatest amount of structural simplicity, that approximate the most closely to an identity of function.

The assemblage of organized beings denominated animals

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and plants, may be collectively represented, in reference to their mutual relationship, by two cones, one of which is inverted on the other, so that their summits are brought into mutual contact. For there is a point of departure common to both of these grand divisions of living nature,—THE ORGANIC CELL,—which animated, commences the animal series, and remaining immovable, serves as the basis of the vegetable creation. This organic cell may be imagined to be situated at the apex of the cones, the lower cone representing the vegetable and the upper one the animal creation. Plants and animals increase in organic simplicity and the analogies between them multiply and become more striking in proportion to their approach to this point; while, on the contrary, the differences which separate them increase and their organization becomes more complicated, as they elongate from it.

All that variety of form which marks the external organs both of plants and animals, is clearly traceable to the same organic laws. Thus, the same organ which attains a high degree of development in one plant or animal, is for certain physiological reasons in another, either suppressed altogether or reduced to a rudimentary condition. But these changes take place almost imperceptibly. We never see an important organ disappear all at once in any of the classes of the animal and vegetable kingdom. It is by degrees that the organ loses in succession the several parts which complicated it; these become rudimentary, and the organ is finally reduced to the utmost degree of structural simplicity, those parts alone remaining which are absolutely essential to enable it to perform its function. What are called varieties by naturalists are, in fact, only different phases in the organic development of the same specific form; and a truly scientific classification can only be achieved in proportion to the accuracy of our perceptions of the natural relationship subsisting among the organs thus modified.

The anterior organs of the different order of vertebrated animals, for instance, are organically modified to the degree of their intelligence, their powers of locomotion, and their peculiar habits. In some quadrupeds they are adapted for the prehension of food and for locomotion; in the bird they are organized for flight; in the fish, for balancing the body and assisting its progress through the water. The twisted arm of the tortoise can be applied to no other purpose than that of creeping, and the enormous hand of the mole can be used only for burrowing. Yet the anterior members in the different orders of the vertebrata consist essentially of the same parts as those which exist in the same members in man. We find in each the same bones, muscles, nerves, and vessels. Yet how different their appearance! how varied their functions! All these ends are attained by a modification in the development of the different parts, one bone being largely developed, a contiguous one less so, some being evolved to a maximum, whilst others are left rudimentary.

We have a manifestation of the same organic law in the vegetable world. Thus the leaves of plants are variously modified so as to be rendered subservient to the exercise of the different vegetative functions. The different organs appended to the vegetable axis and designated as scales, stipules, bracts, sepals, petals, stamens, and pistils, are only a series of leaves in a state of progressive or retrograde development, which have assumed this peculiarity of form in consequence of the peculiar and distinct functions assigned them. A fully developed leaf consists of two parts, a little stalk or support called a petiole, and a flat expanded portion called the blade or limb. In the scale, stipule, and bract, the petiole and lamina of the leaf are reduced to rudimentary condition; in the sepal the former is wholly suppressed and the latter more or less developed. In the petal both lamina and petiole are sometimes present, as in the pink and wall-flower. The petals of these flowers which are broad and expanded at their summit gradually taper into a narrow stalk or petiole, which in this instance is called an unguis, or claw. In the stamen, the petiole is represented by the filament, the lamina by the anther, whilst the reproductive matter called pollen, which is contained in the anther-cells, is only a peculiar transformation of the parenchyma of the leaf. In the pistil, there appears to be the greatest departure from the primitive type; yet-it is not difficult to trace it even in this instance. The pistil is nothing but a folded leaf, the margins of which have united to form a placenta or point of attachment for the ovules, or young germs, which develop along its edge. Other instances might be brought forward illustrative of the fact that the same laws of development and adaptation, govern the organization of both plants and animals.

It is only by viewing nature as a whole that any part of nature can be properly understood. It is to the study of comparative anatomy and physiology, that we are indebted for our knowledge of this identity and unity of organization. The organism of one species has been compared with that of another, and the transitious forms of the several organs have been traced, so that organs are now recognized as the same which were formerly thought to be altogether different. It is to the contributions which they mutually afford each other that we are indebted for the advance of the physical sciences, and the same principle applies to natural history. Almost every part of the human frame has its homologue in some inferior animal. Hence “the advantage—the necessity, rather—of combining a general knowledge of the organization of the lower animals with that of man, which ought always to claim the first attention of the medical student, is now universally recognized. A great part, of the best part, of the proofs of the most important physiological doctrines are derived from comparative anatomy. The increasing taste for the natural sciences, and the rapidly diffusing knowledge of zoology and geology render it scarcely pardonable in a member of a liberal profession to be wholly unversed in them, and almost discreditable to a medical man to be unable to offer any sound opinion on a fossil coral, shell, or bone, which may be submitted to his inspection.”’* So also, the great cell doctrine which is now the basis of animal physiology, had its origin in microscopical investigations into the organization of plants. “Since it ‘has been ascertained that the animal tissues are in their fundamental structure identical with the vegetable tissues, we may expect that botanical investigations may throw as much light upon the animal kingdom, as the study of animals may throw on the vegetable kingdom. Easy as it has been to study the structure of vegetable tissues, so difficult has it been to ascertain their functions, and the work of the various organs in plants, that the most contradictory opinions are entertained upon vegetable functions, upon the circulation of their sap, upon their respiration, and the action of respiration on their fluids. On the contrary, in animal structures the functions are easily traced. The combined action of the various functions upon each other can be easily ascertained. It was the structure, the intimate

* Lectures on the Comparative Anatomy and Physiology of the Invertebrate Animals, delivered at the Royal College of Surgeons: by Richard Owen, F.R. 8.

structure which it was difficult to investigate. And now by referring the result from one kingdom to the other, it is to be hoped that much more rapid progress will be obtained than before.”* Many problems connected with nutrition and reproduction in animals will probably be solved by a more careful observation of these functions in vegetables. A knowledge of cell-life, now universally admitted to be the basis of all scientific physiology, can be best acquired by examining the cells of plants which are much larger than those of animals, and visible to ordinary microscopes at every epoch of their development. The differences which exist among the organic productions are not so great as is commonly thought. There is a oneness in nature which has yet to be understood and appreciated.

One of the most striking differences of organization between the higher orders of animals and plants consists in the presence of a nervo-muscular system in the former of which the latter are totally deprived. This nervo-muscular -system, which is essential to animality, appears to be gradually developed in vegetable life, which thus becomes inseparably bound up with the exercise of the animal functions. It is gradually developed in the inferior orders of animated being, and is manifested most perfectly in man, and those animals the most closely allied to him in organization.

Now comparative anatomy shows that the animal functions of sensation and voluntary motion, manifest themselves in proportion to the more or less perfect condition of the organs appropriated to their exercise. In man, the highest vertebral animal, the organs of the senses and the muscular

* Lectures on Comparative Embryology, delivered before the Lowell Institute in Boston, by Louis Agassiz.

system are the most highly developed, and prove successive degrees of simplification as we descend in the scale. The muscles in the human body are more than five hundred in number, and almost every movement is produced, not by the action of one, but of several of them. The muscular system in man not only moves the body but expresses thought and emotion, and is capable of a very high degree of education. The accomplished tragedian and musician manifest in their performances, the degree to which the muscles of expression and voluntary motion may be educated. The body of man is capable; through the agency of his highly developed nervo-muscular system, of an infinite variety of movement and expression. In man, the muscles of expression are chiefly in the face. In conversation, all persons to a greater or less extent communicate thought by the expression of their countenance. In some, however, the muscles of expression respond more readily to the emotions of the mind than in others, every shade of thought and feeling being beautifully depicted in their faces.* In the inferior animals, the expression of which they are capable is much more limited, and is confined to other parts of the body. The dog wags his tail, the cat elevates her back, the horse erects his ears, and the game-cock spreads out his ruff of feathers on his head. The countenance of the inferior animals is in general devoid of expression. Rage and fear are almost the only passions which are expressed in their faces. Their muscular movements are susceptible of education, as is evident from the performances of dancing dogs and bears,

* Human Physiology designed for Colleges and the Higher Classes in Schools, and for General Reading, by Worthington Hooker, M. D., Professor of the Theory and Practice of Medicine in Yale College. Chapter xiii. page 222.