In 1864, in presenting the Copley medal of the Royal Society to the author of the “Origin of Species,” Major-General Sabine, the President, entered into a full description of the merits of his works, “stamped throughout with the impress of the closest attention to minute details and accuracy of observation, combined with large powers of generalisation.” The award, while highly eulogising the “Origin,” was not however based upon it, but on the more recent botanical writings. “The Fertilisation of Orchids” was described as perhaps the most masterly treatise on any branch of vegetable physiology that had ever appeared; and the fact was justly emphasised that all Darwin’s botanical discoveries had been obtained by the study of some of the most familiar and conspicuous of our native plants, and some of the best-known and easily-procured cultivated exotics.
In 1865 appeared another work from the Darwinian treasury, but in this case it was at first restricted to the Journal of the Linnean Society (vol. ix.), and was not made generally available till the second edition was published separately in 1875. “The Movements and Habits of Climbing Plants” described in the first place the twining of the hop plant, studied by night and day continuously, in a well-warmed room, to which the author was confined by illness. Again and again were different species of plants watched, and the periods in which their shoots revolved noted. The clematises, tropæolums, solanums, gloriosa lilies among leaf-climbing plants; the bignonias, cobæas, bryonies, vines, passion flowers, and other tendril-bearing plants; the ivy, and other root and hook climbers were carefully studied; and botanists for the first time realised fully the advantages which climbing plants possess in the struggle for existence. The climbing faculty depends on a sensitiveness to contact with any firm support, and a most interesting series of modifications has probably, as Darwin suggests, led to the present development of climbing organs, by the spontaneous movement of young shoots and other organs, and by unequal growth.
In concluding, the author made some most profoundly suggestive remarks, which went far to revolutionise our conception of plants. “It has often been vaguely asserted that plants are distinguished from animals by not having the power of movement. It should rather be said that plants acquire and display this power only when it is of some advantage to them; this being of comparatively rare occurrence, as they are affixed to the ground, and food is brought to them by the air and rain. We see how high in the scale of organisation a plant may rise, when we look at one of the more perfect tendril-bearers. It first places its tendrils ready for action, as a polypus places its tentacula. If the tendril be displaced, it is acted on by the force of gravity, and rights itself. It is acted on by the light, and bends towards or from it, or disregards it, which ever may be most advantageous. During several days the tendrils, or internodes, or both, spontaneously revolve with a steady motion. The tendril strikes some object, and quickly curls round and firmly grasps it. In the course of some hours it contracts into a spire, dragging up the stem, and forming an excellent spring. All movements now cease. By growth the tissues soon become wonderfully strong and durable. The tendril has done its work, and has done it in an admirable manner.”
The labour of revising the successive editions of the “Origin of Species,” together with prolonged ill-health, delayed the fulfilment of the promise given in that work, that the facts upon which it was based should be published. It was not till 1868 that the first instalment, “The Variation of Animals and Plants under Domestication,” was given to the world, in two large volumes, with numerous illustrations. The author’s design was to discuss in a second work the variability of organic beings in a state of nature, and the conversion of varieties into species, the struggle for existence and the operation of natural selection, and the principal objections to the theory, including questions of instinct and hybridisation. In a third work it was intended to test the principle of natural selection by the extent to which it explains the geological succession of organic beings, their distribution in past and present times, and their mutual affinities and homologies. The two latter works were never completed, in consequence of ill-health, and the labour involved in dealing with objections to and new facts in support of the “Origin,” and of the other works which at various times it became important to complete. But many portions of these subjects were admirably dealt with by disciples. In some cases Darwin’s views led to the rapid growth of a new science, such as that of comparative embryology, and it would not have been possible for him to cope with and interpret the multitude of new and astonishing facts discovered, which changed the face of organic nature as viewed by biologists. By doing each day the work which seemed most necessary, and which he could best do, Darwin managed, in spite of his infirmity of constitution, to complete a larger body of original work, both in experiment and in thought, together with a greater quantity of bibliographical study and collation of observed facts, than any Englishman perhaps has ever done.
The valuable book on “Variation” records and systematises a vast number of facts respecting all our principal domestic animals and cultivated plants. It gives evidence of wide reading, as well as great diligence in writing letters of inquiry to all living authorities who could give accurate information. Very many visits were paid to zoological gardens, breeders’ establishments, nursery grounds, &c.; and the preparation of skulls, skins, &c., was a frequent occurrence in the Darwinian laboratory. To take the case of rabbits alone, which occupied but a fraction of the time devoted to pigeons: over twenty works are quoted for historical facts, skeletons of various rabbits were prepared and exhaustively compared, the effects of use and disuse of parts traced, most careful measurements are given, and a list of the modifications which domestic rabbits have undergone, with the probable causes, concludes the chapter. As to pigeons, no pigeon-fancier ought to be without the book, for never assuredly was a sporting topic treated by so great a thinker and so admirably. The numerous experiments in crossing different breeds, and the results obtained, make this one of the most instructive books for all breeders. It would seem desirable that this portion of the book should be issued in a separate form. Again, when we turn to the sections on plants we see how indefatigable Darwin was, for he tells us that he cultivated fifty-four varieties of gooseberries alone, and compared them throughout in flower and fruit.
The chapters on Inheritance, and on Reversion to ancestral characters, or atavism, are profoundly suggestive. What can be more wonderful, the author asks, than that some trifling peculiarity should be transmitted through a long course of development, and ultimately reappear in the offspring when mature or even when old? Nevertheless, the real subject of surprise is not that a character should be inherited, but that any should ever fail to be inherited. Gradually leading up to the important hypothesis with which the work closes, he observes that to adequately explain the numerous characters that reappear after intervals of one or more generations, we must believe that a vast number of characters, capable of evolution, lie hidden in every organic being. “The fertilised germ of one of the higher animals, subjected as it is to so vast a series of changes from the germinal cell to old age—incessantly agitated by what Quatrefages well calls the tourbillon vital—is perhaps the most wonderful object in nature. It is probable that hardly a change of any kind affects either parent, without some mark being left on the germ. But on the doctrine of reversion the germ becomes a far more marvellous object, for, besides the visible changes to which it is subjected, we must believe that it is crowded with invisible characters, proper to both sexes, to both the right and left side of the body, and to a long line of male and female ancestors separated by hundreds or even thousands of generations from the present time; and these characters, like those written on paper with invisible ink, all lie ready to be evolved under certain known or unknown conditions.”
Through a further discussion of many deeply interesting facts, about the intercrossing of breeds and species, and about the causes of variability, we pass to the hypothesis of pangenesis, which, briefly stated, supposes that the cells or units of the body are perpetually throwing off minute granules or gemmules, which accumulate in the reproductive system, and may, instead of developing in the next generation, be transmitted in a dormant state through more than one generation and then be developed. Combination in various degrees between these gemmules is supposed to influence their appearance or non-appearance in the offspring at various stages.
This hypothesis certainly gives a picture of a possible mode of accounting for many peculiarities shown by living organisms. Although not generally accepted, it has certainly not been disproved. Mr. Grant Allen’s opinion that it is Darwin’s “one conspicuous failure,” and that it is “crude and essentially unphilosophic,” must be discounted by his known devotion to Mr. Herbert Spencer’s philosophy. If Darwin had been a specialist in modern physiology, he might, perhaps, have expressed his hypothesis in a more persuasive form; but Weismann’s germ plasma theory is the only alternative one hitherto suggested in place of it.