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DARWIN ON ORCHIDS.*

IN reading this extraordinary work—one which is in every way worthy of the great reputation of its author—the words of Shelley, as descriptive of poetry, continually recurred to mind. "Poetry," says the most eloquent of modern poets, "strips the veil of familiarity from the world, and lays bare the hidden and concealed beauties which are the spirits of its forms;" and in a corresponding passage he describes it as "reducing to union under its light yoke all irreconcilable things." That genius, like poetry, also strips the veil of familiarity from the objects of its pursuit, and lays bare the concealed beauties which are the spirits of their forms, is demonstrated in no ordinary manner by the book under notice.

The singular tribe of orchids, or, as they were formerly termed, orchises, with their extraordinary and bizarre forms, so unlike those of flowers in general that they have been constantly likened to and named after objects belonging to the animal kingdom, as flies, bees, butterflies, frogs, old men, monkeys, etc., etc., with their endless diversity of shape, which formerly seemed ''to us in our ignorance," says the author, "as if modelled by the wildest caprice," have been studied by our most skilful botanists. Bauer, Brown, Lindley, and others of high eminence, have described their interesting peculiarities of structure, but have failed to demonstrate the functions of their various parts. Hence orchids have always remained an unsolved enigma, and have been no less attractive to the botanist from the singular irregularity of their form, and their extraordinary mode of growth, than from the uncertainty of the uses of the various parts of their remarkable flowers.

It has remained for one not professedly, or at least, not exclusively, a scientific botanist, to unravel this Gordian knot. Mr. Darwin, whom the world at large regards as a brilliant theorist, but whom those who have the pleasure of his acquaintance know to be a most patient observer, and a most truthful describer of natural phenomena—has, by a series of the most masterly observations, proved the exact co-relation between these flowers and certain nectar or honey-feeding insects. He has proved, moreover, that, with one or two exceptions, they never produce fertile seeds, except by the agency of insect fertilization.

Most persons of modern education are aware that a flower generally consists of four distinct series of organs. These may be briefly described as, an external part, the flower cup or calyx; a second whorl, or circle of parts, termed petals, - usually gaily coloured,—constituting the corolla; and a third series, consisting of bodies called stamens, the most important part of each stamen being a two-celled box, known as the anther, which contains a coloured dust, termed the pollen. This pollen is highly organised, and by its influence, when it is received on the stigma, or adhesive surface of the pistil, or seed-bearing organ, forming the centremost part of the flower, it secures the fertility of the seeds, which would otherwise be sterile.

In most orchids there is a strange irregularity in the flower. Sometimes the calyx is irregular: the corolla is always so. One of its petals, usually the lowermost, is larger than the others, and often assumes the most singular forms. This part secretes nectar to attract insects, and is called the lip, or labellum.

In most orchids there is but one stamen, which is firmly adherent to the upper part of the pistil. Its anther is divided into two cells, which contain pollen, not, however, in the usual form of fine dust, but aggregated into distinct pear-shaped masses, with a short stalk, to the extremity of

* "On the various contrivances by which British and Foreign Orchids are fertilized by Insects." By CHARLES DARWIN, M.A., F.R.S, London: John Murray, 1862.

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each of which is attached a slightly enlarged, exceedingly adhesive or viscid disc.

The stigma, or surface to which the pollen has to be applied, is so situated that, with a few remarkable exceptions, it is impossible that the pollen of the same flower can gain access to it. Hence botanists have hitherto wandered into all kinds of vain speculations as to the mode of fertilization of the seeds of these plants.

Mr. Darwin, with that pains-taking and diligent observation for which he is so remarkably distinguished, has ascertained that the pollen mass of one flower is always carried by insects to a second flower. In the case of our British orchids, the insects which usually perform this duty are various species of moths. These, alighting on the flower, force their way into the nectar-forming labellum. In so doing they come into contact with the anther; the slightest touch opens the elastic case that contains the viscid discs of the pollen masses; these adhere to the insect, which, when plunging into a second flower, applies the pollen to the adhesive surface of the stigma, and so ensures the growth of the seeds. The exact mechanical contrivances by which this effect is secured in the different orchids are so varied, so exquisitely beautiful, so artificial, if we may be allowed the term, as to be almost beyond belief. In the majority of instances, however, they are so complex as not to admit of description, unaided by engravings. We must therefore refer the reader to the work itself.

"The more I study nature," says Mr. Darwin, "the more I become impressed, with ever-increasing force, with the conclusion that the contrivances and beautiful adaptations slowly acquired, through each part occasionally varying in a slight degree, but in many ways, transcend in an incomparable degree the contrivances and adaptations which the most fertile imagination of the most imaginative man could suggest with unlimited time at his disposal."

The main object of Mr. Darwin's book is, not simply to detail the contrivances by which orchids are fertilized, but to show that these contrivances have for their main object the fertilization of each flower by the pollen of another flower. In his volume on the "Origin of Species," Mr. Darwin gave only general reasons for his belief that it is a universal law of nature that organic beings require occasional crossing with other individuals. Having been criticised for publishing this doctrine without giving the facts on which it was founded, he has here gone into the details, so far as regards Orchidaceous plants; and, in accordance with his own views, he has attempted to show that the study of organic beings may be as interesting to an observer who is convinced that the structure of each is due to secondary, laws, as to one who views every detail as a result of the direct interposition of the Creator.

Whatever views may be taken of the author's theoretical considerations, there can be but one opinion as to the value of this work as a most important addition to our stock of scientific knowledge: a tribe of plants, the vital actions of which had proved a stumbling block to all previous investigators, has had the secrets of its structure so far laid bare as to have derived a new interest for all observers. The wonderful co-relation between the instincts of certain insects and the intricate structure of these plants, and their mutual dependence on each other, is most strikingly shown. The fertilization of the seeds of Orchids is due to certain moths, and the food of succeeding generations of moths in subsequent years is due to this fertilization.

Alike to the believer in the doctrine of secondary causes, and to him who takes the older and more orthodox view of Paley and his followers, the present work is one of the highest interest. From this armoury of facts the former will draw many new weapons wherewith to assail the older belief; and the latter, securely entrenched behind his impregnable rampart of faith, may find in its pages new and marvellous instances of design, by the aid of which he may seek to repel the ardent assailants.

We should, however, give an essentially wrong view of this work if aught that we have said should lead to the opinion that it is in any sense controversial, or even theoretical: facts, and facts only, form its basis; and in this point it must be regarded as one of the most remarkable contributions to vegetable physiology that has appeared for many years.

W. B. TEGETMEIER.