Fertilisation of Orchids is a book by English naturalist Charles Darwin published on 15 May 1862 under the full explanatory title On the Various Contrivances by Which British and Foreign Orchids Are Fertilised by Insects, and On the Good Effects of Intercrossing. – Bibliographical introduction from: Freeman, R. B. (1977) The Works of Charles Darwin: An Annotated Bibliographical Handlist. 2nd edn. Dawson: Folkestone. Darwin's previous book, On the Origin of Species, had briefly mentioned evolutionary interactions between insects and the plants they fertilised, and this new idea was explored in detail. Field studies and practical scientific investigations that were initially a recreation for Darwin—a relief from the drudgery of writing—developed into enjoyable and challenging experiments. Aided in his work by his family, friends, and a wide circle of correspondents across Britain and worldwide, Darwin tapped into the contemporary vogue for growing exotic orchids.
The book was his first detailed demonstration of the power of natural selection, and explained how complex ecological relationships resulted in the coevolution of orchids and insects. The view has been expressed that the book led directly or indirectly to all modern work on coevolution and the evolution of extreme specialisation. It influenced botanists, and revived interest in the neglected idea that insects played a part in pollinating flowers. It opened up the new study areas of pollination research and reproductive ecology, directly related to Darwin's ideas on evolution, and supported his view that natural selection led to a variety of forms through the important benefits achieved by cross-fertilisation. Although the general public showed less interest and sales of the book were low, it established Darwin as a leading botanist. Orchids was the first in a series of books on his innovative investigations into plants.
The book describes how the relationship between insects and plants resulted in the beautiful and complex forms which natural theology attributed to a grand designer. By showing how practical adaptations develop from cumulative minor variations of parts of the flowers to suit new purposes, Darwin countered the prevailing view that beautiful organisms were the handiwork of a Creator. Darwin's painstaking observations, experiments, and detailed dissection of the flowers explained previously unknown features such as the puzzle of Catasetum, which had been thought to have three completely different species of flowers on the same plant. In addition, they produced testable predictions including his then-controversial proposal that the long nectary of Angraecum sesquipedale meant that there must be a moth with an equally long proboscis. This was confirmed in 1903 when Xanthopan morganii praedicta was found in Madagascar.
Background Charles Darwin grew up with an interest in natural history, and as a student at the University of Cambridge he became a pupil and close friend of botany professor John Stevens Henslow. The year he graduated, Darwin was given a supernumerary position as a gentleman naturalist and geologist on the second voyage of HMS Beagle, a trip that lasted five years. By the time he returned in October 1836, he had doubts about the doctrine that species were fixed and unchanging. Within months, experts informed him that specimens he had collected were separate species, not just varieties, and the patterns he saw inspired the inception of his theory of natural selection in 1838. Darwin began editing and publishing the expert reports, collected in the Zoology of the Voyage of H.M.S. Beagle, at the same time as writing a series of books on geology, the first of which was The Structure and Distribution of Coral Reefs. His "species work" was his "prime hobby", a background to this writing, but it evolved into an extensive research programme during the twenty years before he published his theory.
Insect fertilisation of plants Darwin's speculations on the origin of species convinced him that cross-fertilisation played an important role in keeping specific forms consistent. He rejected the doctrine that the characteristics of a species were static, and was aware from animal husbandry that inbreeding could lead to changes, often deleterious. He thought that natural outbreeding through cross-fertilisation would keep wild species homogenous yet vigorous. Cross-fertilisation would confer an evolutionary advantage by spreading favourable changes throughout a reproductive community. His ideas were contrary to the common supposition that plants were usually self-fertilising, and so every summer Darwin investigated the contribution of insect pollination to the cross-pollination of flowers.
In the summer of 1841 Charles and Emma Darwin moved from the turmoil of London to the countryside, to Down House, a quiet former parsonage in the village of Downe. He wrote, "The flowers are here very beautiful". Darwin followed the recommendation of his friend, the leading botanist Robert Brown, and read Das entdeckte Geheimnis der Natur im Bau und in der Befruchtung der Blumen (The Secret of Nature in the Form and Fertilisation of Flowers Discovered). The little known book, published in 1793 by Christian Konrad Sprengel but never translated into English, introduced the idea that flowers were created by God to fulfill a teleological purpose: insects would act as "living brushes" to cross-fertilise plants in a symbiotic relationship. This functional view was rejected and mostly forgotten, as it contradicted the common belief that flowers had been created for beauty, and were generally self-fertilising. For Darwin, the concept of evolution gave new meaning to Sprengel's research into the mechanisms for cross-fertilisation. He welcomed its support for his supposition that cross-fertilisation in flowering plants tended to allow their offspring to avoid possible disadvantages resulting from self-fertilisation, and by 1845 he had verified many of Sprengel's observations.
A favourite walk took the Darwin family to a spot above the quiet Cudham valley, teeming with orchids including Cephalanthera, Neottia, fly orchids and musk orchids. They called this place "Orchis Bank", and the whole family became involved in Darwin's researches. Darwin observed orchids every summer, but in twenty years, only on two occasions (when he noticed butterflies "sucking O. pyramidalis and Gymnadenia") did he see insects visiting flowers. In 1854, Darwin began to work full-time on the origin of species. He examined orchids and counted how often one or both pollinia (pollen masses) had been removed from their flowers, indicating that they had been visited by insects. He experimented with insect pollination to investigate whether, by cross-fertilising field crops such as Fabaceae, they would yield more vigorous offspring, and published letters about his inconclusive results in The Gardeners' Chronicle in 1857 and 1858. He next applied Sprengel's methods to empirical research on orchids., Despite delays caused by recurring illness, he made progress on writing his planned "Big Book" on evolution, but when Alfred Russel Wallace's letter prompted joint publication of both of their theories of natural selection in 1858, Darwin quickly wrote On the Origin of Species as an abstract of his theory, published on 22 November 1859. In this book, he gave credence to Sprengel's ideas on the advantages of "intercrossing", and noted: "Many of our orchidaceous plants absolutely require the visits of moths to remove their pollen masses and thus to fertilise them". He introduced his new concept, the process of coevolution, describing the co-adaptation of bumblebees and red clover, and speculating "how a flower and a bee might slowly become, either simultaneously or one after the other, modified and adapted in the most perfect manner to each other, by the continued preservation of individuals presenting mutual and slightly favourable deviations of structure". This was a theme he developed in his orchid book.
Botany as recreation
After On the Origin of Species was published, Darwin became involved in producing revised editions as well as working on Variation of Animals and Plants Under Domestication as the first part of his planned "Big Book". By the spring of 1860 he had tired of the grind of writing, and needed something fresh and interesting to study. During a family visit to relatives at Hartfield, he was searching for orchids when he noticed a sundew. He collected it and tried to feed it insects, thus beginning a long-term study of insectivorous plants. He investigated other botanical questions raised by his ideas of natural selection, including the advantages of sexual dimorphism in primulas, and the adaptive mechanisms that ensure cross-pollination in orchids., from The Correspondence of Charles Darwin, Volume 8: 1860 (pub 1993) As an enthusiastic practical scientist, such investigations gave him a strong sense of personal enjoyment. He relished pitting his wits against nature, and following lucky hunches. His theory was a way of looking at the world, enabling him to find creative solutions to problems that traditional approaches could not solve. He later wrote, "I am like a gambler, & love a wild experiment."
Around the end of April 1860, Darwin discussed insect pollination with his friend Joseph Dalton Hooker, and mentioned the bee orchid. Darwin corresponded with Hooker's assistant Daniel Oliver, the senior curator at Kew Gardens, who became a follower of Darwin's ideas. At the start of June, Darwin wrote to The Gardeners' Chronicle asking for readers' observations on how bee or fly orchids were fertilised. His letter described the mechanisms for insect fertilisation he had discovered in common British orchids, and reported his experimental observations that pollen masses were removed from Orchis morio and Orchis mascula plants in the open, but left in their pouches in adjacent plants under a glass bell jar. He wrote to American botanist Asa Gray that he had been "so struck with admiration at the contrivances, that I have sent notice to Gardeners Chronicle", and made similar enquiries of other experts.
Darwin became engrossed in meticulous microscopic examination, tracing the complicated mechanisms of flowers that attracted insects by their nectar so that the insects transported pollen to cross-pollinate other plants, and on 19 July he told Hooker, "I am intensely interested on subject, just as at a game of chess." In September, he "dissected with the greatest interest" and wrote, "The contrivances for insect fertilisation in Orchids are multiform & truly wonderful & beautiful." By October, he had "a large mass of notes with many new facts", but set them aside "convinced that I ought to work on Variation & not amuse myself with interludes".
Research and draft