Contrivances by Which Orchids Are Fertilised by Insects. This was also published by D. Appleton & Company of New York in 1877, and a German translation was published in the same year. Despite being well praised by botanists, only about 6,000 copies of the English editions had been sold by 1900. Content Darwin set out a detailed study of common descent with modifications by expanding on the theme of coevolution between local populations of insects and flowering plants that he had briefly discussed in On the Origin of Species. He examined numerous ways in which orchids vary, showing how they had diverged and developed specialised pollen-dispersal mechanisms. The intricate morphology and anatomy of each flower was carefully described. Apparently trivial details were examined in relation to natural selection to demonstrate how slight variations in similar structures of closely related flowers led to specialised modifications that provided various pollinators (insects) with different ways to cross-fertilise. The mass of descriptive detail was a great achievement, but the result is demanding to read. In the introduction, Darwin explained his aim of meeting complaints that detailed support for his theory was lacking in On the Origin of Species. He chose orchids for his subject as "amongst the most singular and most modified forms in the vegetable kingdom" in the hope of inspiring work on other species, and felt that "the study of organic beings may be as interesting to an observer who is fully convinced that the structure of each is due to secondary laws, as to one who views every trifling detail of structure as the result of the direct interposition of the Creator." He gave due credit to previous authors who had described the agency of insects in fertilising orchids, and all who had helped him. British orchids In the first chapter Darwin described the British orchids he had studied, giving detailed explanations of their various mechanisms for transferring pollen to insects. The first mechanism described is that of Orchis mascula, which serves as an introduction to the explanation of other Orchidaceae. In the upper part of the flower a petal shelters the male organ which has two packages of pollen grains, held together by thin elastic threads. These pollen masses stand side by side and have stalks down to adhesive balls in a cup which keeps them moist and sticky. When an insect lands on the large projecting lower petal, the