An introduction to Darwin's Fertilisation of Orchids (1862 and 1877)

by Gordon Chancellor

During the 1840s and early 1850s Charles Darwin established his scientific reputation with a series of books based on his Beagle discoveries, while privately developing his theory of evolution by natural selection. As is well known, he had no intention of publishing his theory until all the evidence was ready. He was in the process of writing his "big book" when his hand was forced by the arrival of a letter in 1858 containing an outline of a strikingly similar theory from Alfred Russel Wallace.

Darwin's Origin of species came out at the end of 1859 but he insisted it was just a stop gap, with no room for the references or footnotes which he regarded as essential for his theory's credibility. In the event the Origin proved sufficient to establish his theory among scientists and marked the real beginning of evolutionary biology. It also triggered a storm of non-scientific controversy, as Darwin knew it would, by arguing that species were not divinely created but were instead 'by products' of a gradual natural process of descent with modification. Although he barely mentioned human origins, for some readers Darwin's implication that we are descended from an ape-like ancestor was profoundly disturbing.

Even with the enormous success of the Origin, Darwin still believed he needed to present the detailed evidence underpinning his theory and he attempted to answer his critics in two new editions of the Origin (1860 and 1861) and a vast correspondence. In almost perpetual poor health and worn out by work and family troubles, in 1861 Darwin needed some less frenetic scientific diversion, so he returned to an earlier research topic which he could easily pursue at home. He had been interested in orchids for at least twenty years and knew that they demonstrated the need for cross-fertilisation, a topic central to his theory of evolution and of deep personal interest to him.

On the various contrivances by which British and Foreign orchids are fertilised by insects and on the good effects of inter-crossing appeared in May 1862 and was the first of Darwin's books following the Origin. Orchids was based on years of patient observation and experimentation accelerated the previous summer by an opportunity for nature study with his children on a family seaside 'holiday'. It was essentially a monograph describing the structure of a range of orchid flowers, with detailed analysis of their form and function.

In his introductory chapter, to help his readers understand the rest of the book, Darwin provided an 'explanation of terms' for the parts of an orchid flower, namely: stamen, pistil, anther, stigma, rostellum, viscid disc, pedicel, caudicle, pollinia, sepal, petal and labellum. He interpreted the flower as a system for attracting various insects, and forcing them to act as 'mules' for carrying its pollen to another individual plant of the same species, thereby ensuring at least occasional cross-pollination.

Darwin showed how the flower's intricate structure is the result of gradual descent with modification of the parts of simpler ancestral forms, noting that the functions of the separate parts may have been different in the past from what they are today. In this respect it is a methodological masterclass in the scientific use of history, showing how homologies between flower parts – these had been elucidated by previous botanists – allow us to model past evolutionary events. This method of comparing a range of closely similar plants and estimating their degrees of relatedness, thus giving us clues to their history, was the method Darwin had used twenty years previously in working out The structure and distribution of coral reefs in 1842. The use of homologies to aid classification and build up a picture of the evolutionary relationships of the various kinds of orchids was also the same as Darwin had used in his monographs on Cirripedes in the 1850s. Those far more technical works pre-dated the Origin and were not written for the general reader, so the evolutionary philosophy behind them was implicit. In Orchids the evolutionary perspective was obvious, as for example in the following passage discussing the value of homologies (emphasis added):

The importance of the science of Homology rests in its giving us the key-note of the possible amount of difference in plan within any group; it allows us to class under proper heads the most diversified organs; it shows us gradations which would otherwise have been overlooked, and thus aids us in our classification; it explains many monstrosities; it leads to the detection of obscure and hidden parts, or mere vestiges of parts, and shows us the meaning of rudiments. Besides these practical uses, to the naturalist who believes in the gradual modification of organic beings, the science of Homology clears away the mist from such terms as the scheme of nature, ideal types, archetypal patterns or ideas, &c.; for these terms come to express real facts. The naturalist, thus guided, sees that all homological parts or organs, however much diversified, are modifications of one and the same ancestral organ; in tracing existing gradations he gains a clue in tracing, as far as that is possible, the probable course of modification during a long line of generations. He may feel assured that, whether he follows embryological development, or searches for the merest rudiments, or traces gradations between the most different beings, he is pursuing the same object by different routes, and is tending towards the knowledge of the actual progenitor of the group, as it once grew and lived. Thus the subject of Homology gains largely in interest. (pp. 287-288)

Throughout the book Darwin showed how natural selection can create exquisite co-adaptations between plants and animals and in so doing it founded the science of pollination ecology. He was even able to make predictions based on understanding that the extraordinary morphology of orchid flowers is co-adapted to the morphology and behavior of their pollinating species. He suggested (p. 197) that a moth with an incredibly long proboscis would be discovered to be the pollinator of the orchid Angraecum sesquipedale, specimens of which had been sent to him from Madagascar. Sure enough, some forty years later the moth was duly discovered, albeit too late for Darwin. It also demonstrated the relentless need for sexual reproduction in nature to provide variation for natural selection to sift between. Some religious Victorians raised on the Bridgewater Treatises may have been horrified by the idea of a beautiful flower as a sex contraption – Darwin called it a 'contrivance' - cobbled together from the plant parts bin.

Orchids was the first of the botanical books which Darwin published from 1862, all of which 'exalted' plants and showed how closely linked to animals they are. Several of these books, such as Cross and self-fertilisation (1876), developed the sexual theme initiated in Orchids. Until the end of his life in 1882 Darwin also wrote books on variation, heredity, human evolution, sexual selection, emotions and earthworms, leaving a vast evolutionary agenda for future generations of scientists. Orchids started the process of building on the foundation of the Origin unshackled from the need to argue for the fact of evolution. Darwin used Orchids as the perfect vehicle for showing the power of natural selection with no need for God's involvement, thereby nullifying at a stroke the old 'argument from design':

The more I study nature, 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 in many ways, with the preservation or natural selection of those variations which are beneficial to the organism under the complex and ever-varying conditions of life, 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. (p. 351)

The book is fundamentally about sexual reproduction and seems reminiscent of some of his grandfather Erasmus Darwin's works, such as The loves of the plants (1789; see Browne 1989). Erasmus Darwin had championed the theory that plants reproduced sexually at a time when this was still not universally accepted and it is well known that as a young man Charles Darwin was inspired by his grandfather's work.

Orchids appeared in May 1862 and there were probably only 2,000 copies printed. Although highly praised by botanists at the time, it never sold well. Darwin updated his orchid research in a paper in 1869 and incorporated these updates in the second edition of 1877. The two editions are basically the same although there are differences: the second edition has fewer pages but this is because it uses a smaller print size; it has chapter headings where the first edition has none; there are more chapters (nine as opposed to seven in the first edition) and the order in which the genera of orchids are treated differs somewhat between the two editions. Significantly, the final paragraph was rewritten and the last passage from the first edition was dropped.

Orchids has been translated into at least seven other languages; Darwin Online includes the book in Chinese, French, Italian and German.

Gordon Chancellor, July 2019

Edited by John van Wyhe

RN2

Browne, Janet. 1989. Botany for gentlemen: Erasmus Darwin and "The Loves of the Plants". Isis 80:593-621. https://dash.harvard.edu/bitstream/handle/1/3353945/Browne_Botany.pdf?sequence=2&isAllowed=y

 

1862. On the various contrivances by which British and foreign orchids are fertilised by insects. Text Image PDF F800

1877. The various contrivances by which orchids are fertilised by insects. 2d ed. Text Image PDF F801

1877. The various contrivances by which orchids are fertilised by insects. New York: Appleton. 2d ed., revised. Image PDF F802

1882. The various contrivances by which orchids are fertilised by insects. 2d ed., revised. 3d thousand. Text Image PDF F803

Chinese

1965. 兰花的传粉: 兰花借助于昆虫传粉 的种种技巧. 228页. 唐进, 汪发缵, 陈心啓, 胡昌序译. 北京: 北京科学出版社. PDF F817c

French

1870. De la fécondation des orchidées par les insectes et des bons résultats du croisement. Text Image PDF F818

German

1862. Die verschiedenen Einrichtungen durch welche Orchideen von Insecten befruchtet werden. PDF F820

1877. Die verschiedenen Einrichtungen durch welche Orchideen von Insecten befruchtet werden. Text Image PDF F821

Italian

1883. I diversi apparecchi col mezzo dei quali le orchidee vengono fecondate dagli insetti. Image PDF F823

1964. Efectele fecundarii incrucisate si ale autofecundarii in regnul vegetal. Diferitele dispozitive cu ajutorul carora orhideele sint fecundate de catre insecte. PDF F1271

 

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