6 withstanding their name, are born from eggs, as well as birds, fishes, and reptiles. This principle also excludes that supposed production of organized beings without parents (of worms in corrupted matter, for instance,) which was formerly called spontaneous generation; and the best physiologists of modern times agree in denying the reality of such a mode of generation." Sect. 2.-The Examination of the Process of Reproduction in Vegetables. THE extension of the analogies of animal generation to the vegetable world was far from obvious. This extension was however made;— with reference to the embryo plant, principally by the microscopic observers, Nehemiah Grew, Marcello Malpighi, and Antony Leeuwenhoek;-with respect to the existence of the sexes, by Linnæus and his predecessors. The microscopic labors of Grew and Malpighi were patronized by the Royal Society of London in its earliest youth. Grew's book, The Anatomy of Plants, was ordered to be printed in 1670. It contains plates representing extremely well the process of germination in various seeds, and the author's observations exhibit a very clear conception of the relation and analogies of different portions of the seed. On the day on which the copy of this work was laid before the Society, a communication from Malpighi of Bologna, Anatomes Plantarum Idea, stated his researches, and promised figures which should illustrate them. Both authors afterwards went on with a long train of valuable observations, which they published at various times, and which contain much that has since become a permanent portion of the science. Both Grew and Malpighi were, as we have remarked, led to apply to vegetable generation many terms which imply an analogy with the generation of animals. Thus, Grew terms the innermost coat of the seed, the secundine; speaks of the navel-fibres, &c. Many more such terms have been added by other writers. And, as has been observed by a modern physiologist, the resemblance is striking. Both in the vegetable seed and in the fertilized animal egg, we have an embryo, chalazæ, a placenta, an umbilical cord, a cicatricula, an amnios, membranes, nourishing vessels. The cotyledons of the seed are the equivalent of the vitellus of birds, or of the umbilical vesicle of sucking-beasts: 6 Bourdon, p. 221. 8 the albumen or perisperm of the grain is analogous to the white of the egg of birds, or the allantoid of viviparous animals. Sexes of Plants.-The attribution of sexes to plants, is a notion which was very early adopted; but only gradually unfolded into distinctness and generality. The ancients were acquainted with the fecundation of vegetables. Empedocles, Aristotle, Theophrastus, Pliny, and some of the poets, make mention of it; but their notions were very incomplete, and the conception was again lost in the general shipwreck of human knowledge. A Latin poem, composed in the fifteenth century by Jovianus Pontanus, the preceptor of Alphonso, King of Naples, is the first modern work in which mention is made of the sex of plants. Pontanus sings the loves of two date-palms, which grew at the distance of fifteen leagues from each other: the male at Brundusium, the female at Otranto. The distance did not prevent the female from becoming fruitful, as soon as the palms had raised their heads above the surrounding trees, so that nothing intervened directly between them, or, to speak with the poet, so that they were able to see each other. Zaluzian, a botanist who lived at the end of the fifteenth century, says that the greater part of the species of plants are androgynes, that is, have the properties of the male and of the female united in the same plant; but that some species have the two sexes in separate individuals; and he adduces a passage of Pliny relative to the fecundation of the date-palm. John Bauhin, in the middle of the seventeenth century, cites the expressions of Zaluzian; and forty years later, a professor of Tübingen, Rudolph Jacob Camerarius, pointed out clearly the organs of generation, and proved by experiments on the mulberry, on maize, and on the plant called Mercury (mercurialis), that when by any means the action of the stamina upon the pistils is intercepted, the seeds are barren. Camerarius, therefore, a philosopher in other respects of little note, has the honor assigned him of being the author of the discovery of the sexes of plants in modern times.10 The merit of this discovery will, perhaps, appear more considerable when it is recollected that it was rejected at first by very eminent botanists. Thus Tournefort, misled by insufficient experiments, maintained that the stamina are excretory organs; and Reaumur, at the beginning of the eighteenth century, inclined to the same doctrine. 9 9 Mirbel, El. ii. 538. 10 Mirbel, ii. 539. Upon this, Geoffroy, an apothecary at Paris, scrutinized afresh the sexual organs; he examined the various forms of the pollen, already observed by Grew and Malpighi; he pointed out the excretory canal, which descends through the style, and the micropyle, or minute orifice in the coats of the ovule, which is opposite to the extremity of this canal; though he committed some mistakes with regard to the nature of the pollen. Soon afterwards, Sebastian Vaillant, the pupil of Tournefort, but the corrector of his error on this subject, explained in his public lectures the phenomenon of the fecundation of plants, described the explosion of the anthers, and showed that the florets of composite flowers, though formed on the type of an androgynous flower, are sometimes male, sometimes female, and sometimes neuter. But though the sexes of plants had thus been noticed, the subject drew far more attention when Linnæus made the sexual parts the basis of his classification. Camerarius and Burkard had already entertained such a thought, but it was Linnæus who carried into effect, and thus made the notion of the sexes of vegetables almost as familiar to us as that of the sexes of animals. Sect. 3.-The Consequent Speculations.-Hypotheses of Generation. THE views of the processes of generation, and of their analogies throughout the whole of the organic world, which were thus established and diffused, form an important and substantial part of our physiological knowledge. That a number of curious but doubtful hypotheses should be put forward, for the purpose of giving further significance and connexion to these discoveries, was to be expected. We must content ourselves with speaking of these very briefly. We have such hypotheses in the earliest antiquity of Greece; for as we have already said, the speculations of cosmogony were the source of the Greek philosophy; and the laws of generation appeared to offer the best promise of knowledge respecting the mystery of creation. Hippocrates explained the production of a new animal by the mixture of seed of the parents; and the offspring was male or female as the seminal principle of the father or of the mother was the more powerful. According to Aristotle, the mother supplied the matter, and the father the form. Harvey's doctrine was, that the ovary of the female is fertilized by a seminal contagion produced by the seed of the male. But an opinion which obtained far more general reception was, that the embryo pre-existed in the mother, before any union of the sexes.11 It is easy to see that this doctrine is accompanied with great difficulties;12 for if the mother, at the beginning of life, contain in her the embryos of all her future children; these embryos again must contain the children which they are capable of producing; and so on indefinitely; and thus each female of each species contains in herself the germs of infinite future generations. The perplexity which is involved in this notion of an endless series of creatures, thus encased one within another, has naturally driven inquirers to attempt other suppositions. The microscopic researches of Leeuwenhoek and others led them to the belief that there are certain animalcules contained in the seed of the male, which are the main agents in the work of reproduction. This system ascribes almost everything to the male, as the one last mentioned does to the female. Finally, we have the system of Buffon;—the famous hypothesis of organic molecules. That philosopher asserted that he found, by the aid of the microscope, all nature full of moving globules, which he conceived to be, not animals as Leeuwenhoek imagined, but bodies capable of producing, by their combination, either animals or vegetables, in short, all organized bodies. These globules he called organic molecules.13 And if we inquire how these organic molecules, proceeding from all parts of the two parents, unite into a whole, as perfect as either of the progenitors, Buffon answers, that this is the effect of the interior mould; that is, of a system of internal laws and tendencies which determine the form of the result as an external mould determines the shape of the cast. 14 An admirer of Buffon, who has well shown the untenable character of this system, has urged, as a kind of apology for the promulgation of the hypothesis, that at the period when its author wrote, he could not present his facts with any hope of being attended to, if he did not connect them by some common tie, some dominant idea which might gratify the mind; and that, acting under this necessity, he did well to substitute for the extant theories, already superannuated and confessedly imperfect, conjectures more original and more probable. Without dissenting from this view, we may observe, that Buffon's theory, like those which preceded it, is excusable, and even deserving of admiration, so far as it groups the facts consistently; because in doing this, it exhibits the necessity, which the physiological speculator ought to feel, of aspiring to definite and solid general principles; and that thus, though 13 lb. p. 219. 14 Ib. p. 221. 11 Bourdon, p. 204. 12 Ib. p 209. the theory may not be established as true, it may be useful by bringing into view the real nature and application of such principles. It is, therefore, according to our views, unphilosophical to derive despair, instead of hope, from the imperfect success of Buffon and his predecessors. Yet this is what is done by the writer to whom we refer. "For me," says he,15 "I vow that, after having long meditated on the system of Buffon,-a system so remarkable, so ingenious, so well matured, so wonderfully connected in all its parts, at first sight so probable;-I confess that, after this long study, and the researches which it requires, I have conceived in consequence, a distrust of myself, a skepticism, a disdain of hypothetical systems, a decided predilection and exclusive taste for pure and rational observation, in short, a disheartening, which I had never felt before." The best remedy of such feelings is to be found in the history of science. Kepler, when he had been driven to reject the solid epicycles of the ancients, or a person who had admired Kepler as M. Bourdon admires Buffon, but who saw that his magnetic virtue was an untenable fiction, might, in the same manner, have thrown up all hope of a sound theory of the causes of the celestial motions. But astronomers were too wise and too fortunate to yield to such despondency. The predecessors of Newton substituted a solid science of Mechanics for the vague notions of Kepler; and the time soon came when Newton himself reduced the motions of the heavens to a Law as distinctly conceived as the Motions had been before. CHAPTER V. EXAMINATION OF THE NERVOUS SYSTEM, AND Consequent IT Sect. 1.-The Examination of the Nervous System. T is hardly necessary to illustrate by further examples the manner in which anatomical observation has produced conjectural and hypothetical attempts to connect structure and action with some 15 Bourdon, p. 274. |