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CHARLES DARWIN.

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Supplement, Jan. 1, 1876.] THE GARDEN.

CHARLES DARWIN.

Mr. Darwin is one of the profoundest thinkers of the present day, and to be so, in this intellectual age, is to be a king among men. Although he has achieved his greatest triumphs in fields with which we have little connection, yet the interest he has taken in plants and plant life clearly identifies him with horticulture. Mr. Darwin's first work, and still to our mind his best work, is his "Journal of His Voyage as Naturalist of the 'Beagle.'" This may not inaptly be called the "Waverley" novel of naturalists. We may not have read it quite so often as the "Antiquary" or "Rob Roy;" but, as with them, whenever we do re-read it we do so with renewed pleasure. There is a freshness and clearness about it, combined with a power of description that never palls—and there is the same delightful under-current of thought upon every subject that gives such a charm to his other works; he not only sees what is before him and tells one what he sees in vivid language, but turns it over in his mind, and takes one along with him, confidentially as it were, as he does so. To our mind it is one of the most delightful books in the English language. His subsequent, and what we suppose we must call his greater, works have probably, from their very nature, less of clearness, freshness, and simplicity than the "Journal." From the "Journal" we could cite many passages having interest for the horticulturist. Take the following description of tropical scenery in South America:—"When quistly walking along the shady pathways, and it admiring each successive view, one wishes to find language to express one's ideas. Epithet after epithet is found too weak to convey to those who have not visited the inter-tropical regions the sensation of delight which the mind experiences. I have said the plants in a hothouse fail to communicate a just idea of the vegetation, yet I must recur to it. The land is one great wild, untidy, luxuriant hothouse, which Nature made for her menagerie, but man has taken possession of it, and has studded it with gay houses and formal gardens. How great would be the desire in every admirer of Nature to behold, if such were possible, the products of another planet; yet, to every one in Europe, it may be truly said, that at the distance of a few degrees from his native soil the glories of another world are open to him. In my last walk, I stopped again and again to gaze on these beauties, and endeavoured to fix for ever in my mind an impression, which, at the time, I knew, sooner or later must fail. The form of the Orange tree, the Cocoa-nut, the Palm, the Mango, the tree Fern, the Banana will remain clear and separate; but the thousand beauties which unite these into one perfect scene must fade away; yet they will leave, like a tale heard in childhood, a picture full of indistinct but most beautiful figures." Turn again to his observations on the character of the southern part of America in relation to the production of fruit. "The climate of the southern part of South America presents many phenomena of the highest interest. It has long been observed that there exists some essential difference between it and that of the countries in the northern hemisphere. I have already remarked on the surprising contrast between the rank vegetation of the broken west coast, consequent on the humid climate, as compared with the dry and sterile plains of Patagonia. The clouded and boisterous state of the atmosphere is necessarily accompanied by a decrease in extreme temperature; hence we find that fruits which ripen well, and are very abundant—such as the Grape and Fig—in latitude 41°, on the east coast, succeed very poorly in a lower latitude on the opposite side of the Continent. The result is more strongly marked if we take Europe as the standard of comparison. In Chiloe, latitude 42°, corresponding to the northern parts of Spain, Peaches require the greatest care, and seldom produce fruit, but Strawberries and Apples succeed to admiration. At Valdivia, latitude 40°, or that of Madrid, standard Peaches bear abundantly, Grapes and Figs ripen, but are far from common, Olives seldom even partially ripen, and Oranges not at all, yet in Europe this is the parallel most productive of these fruits. Even at Conception, latitude 36°, Oranges are not abundant, though the other named fruits succeed perfectly. At the Falklands, in the same latitude as the south of England, Wheat very seldom comes to maturity; but we ought to feel little surprise at this when we hear that in Chiloe, latitude 42°, the inhabitants are frequently compelled to cut their Corn before it is ready and bring it into their houses to dry."

Such notices as the following, too, of plants or vegetable productions met with in his travels are frequent. At Chiloe he "one day noticed some very fine plants of the Panke (Gunnera scabra), which somewhat resembles the Rhubarb on a gigantic scale, growing on the sandstone cliffs. The inhabitants eat the stalks, which are sub-acid, and tan leather with the roots, and prepare a black die from them. The leaf is nearly circular, but deeply indented on its margin; I measured one which had a diameter of nearly 8 feet, and, therefore, a circumference of no less than 24 feet! The stalk is rather more than a yard high, and each plant sends out four or five of these enormous leaves, presenting altogether a very noble appearance."

It will thus be seen that from the very first, and even in a work so unlikely to elicit them, as the journal of a sea voyage, plants and horticulture occupied a fair share of his attention.

His next great work in which plant life occupies much attention was the origin of species, and here we are sure we need not remind the reader that many of his arguments and illustrations are drawn

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from the phenomena observed by himself in horticulture or recorded by horticulturists. We are not going to re-open any of the questions discussed in that work, but we may be allowed to cite Mr. Darwin himself in illustration of some of the positions taken by him in it. Starting from the admitted transmission of qualities from parents to their children, he argued for their gradual alteration by process of natural selection into general progression, improvement, or better adaptation for their condition of life. Now, we have in him an example of both—we have a striking instance of the transmission of qualities by men to their descendants, and we have also an example of the fact that while the identity of the qualities cannot be disputed, neither can the fact of an alteration in them for the better be denied. No one can have read the works of Dr. Erasmüs Darwin—"Zoonomia," "The Botanic Garden, or the Loves of the Plants," without recognising in them much of the same qualities of intellect that are characteristic of his descendant.

His succeeding works still more directly interest the horticulturist. These consist of his papers on the "Dimorphism of the Primrose, of Linum, and of Lythrum Salicaria," and also those on the "Character and Hybrid-like Nature of the Offspring from the Illegitimate Unions of Dimorphic and Trimorphic Plants," his larger work on the "Variation of Animals and Plants under Domestication," his work on the "Various Contrivances by which British and Foreign Orchids are Fertilised by Insects, and on the good effects of Crossing," his paper on the "Movements and Habits of Climbing Plants," and lastly, his work on "Insectivorous Plants,'' which latter we have only lately reviewed in this journal, and need not therefore again recur to. All these bear directly in some form or other on the cultivation and propagation of plants under cultivation. Those relating to the dimorphism or trimorphism of certain plants and the crossing of them, have thrown a flood of light on the phenomena of hybridisation—all tending to show that there is no more reason to think that spccies have been specially endowed with various degrees of sterility to prevent them crossing and blending in Nature, than to think that trees have been specially endowed with various and somewhat analogous degrees of difficulty in being grafted together in order to prevent them becoming inarched in our forests. The proof of this commenced with Mr. Darwin asking Nature the meaning and purpose of the difference between pin-eyed and thrum-eyed Primroses. From one step to another, sometimes with the concurrent assistance of other observers, such as Mr. Scott, then in the Royal Botanic Gardens, Edinburgh, but chiefly by his own independent observations, Mr. Darwin extended his experiments on their comparative fertility over a large number of species of Primula, Linum, and Lythrum, and established, beyond a doubt, that whether the Primrose was pin-eyed or thrum-eyed, that is, whether or not the style or the stamens were to be seen at the mouth of the tube of the corolla—in other words, wherever the one was longer than the other, they were unable adequately to fertilise the ovary; whereas, if neither was visible at the mouth of the corolla, which was found to be equivalent to their both being at the same level half way down, then they fertilised completely. The first natural inference, of course, would be that the unfertility of the pin-eyed or thrum-eyed flower was due to the style and stamens being stationed at a distance from each other, but Mr. Darwin at once removed this element of error by going through the process of trying to fertilise them artificially. The pollen, too, was found to be of different dimensions in the two cases, and the style also different. When the experiment was made with different flowers, the stamens of the thrum-eyed flower were found to fertilise the pin-eyed style, both being at the same level at the mouth of the tube of the corolla, while the stamens of the pin-eyed flower fertilised the style of the thrum-eyed flower, they being each respectively situated low down in the tube of their corolla. This was only an experiment with other flowers of the same species, but it was also shown that in experimenting with distinct species the pollen of one of the two forms of the same species, and not of the other, will fertilise a distinct species. It has long been known that A will fertilise B, and B will not fertilise A; but the extension of such an exception to the two forms of the same individual flower was a new and important step. Further, although the attempt to fertilise the pin-eyed and thrum-eyed flowers with the pollen of their own stamens, may, in a general way, be called ineffectual (that is, that they produced a good deal less seed than the other unions), they were not absolutely and completely sterile, but Mr. Darwin found a remarkable resemblance in many points between the seed so obtained and their offspring, and those of hybrid unions between different species. We must refer the reader to Mr. Darwin's papers for these points of resemblance, besides much other interesting information, contenting ourselves with saying that the opinion expressed by Mr. Darwin on the subject in 1864, seems to us still well founded. "Although good is gained," said he, "by the inevitable crossing of the dimorphic flowers, yet numerous other analogous facts lead me to conclude that some other quite unknown law of Nature is here dimly indicated to us."

We cannot follow this subject further, nor have we left ourselves space to expatiate as we should like to do on his interesting paper on "Climbing Plants," and on the contrivances whereby Mr. Darwin shows that certain Orchids and other plants are alone fertilised by insect agency. Both are full of details worked out with the greatest care, and both are replete with instances of remarkable adaptation of structure to purpose—what the natural theologian calls evidences of design. So marked are these that one of Mr. Darwin's followers and admirers, writing recently in the pages of one of our contemporaries, enthusiastically exclaims, "Thanks to the laborious experiments of Darwin—thanks to the example he has set, the purpose of this, as of many other points of structure passed over before as merely curious, has been made apparent. No more persuasive apostle of natural theology, no more powerful advocate of the argument furnished by design and adaptation, ever lived than Charles Darwin."

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