Different Forms of Flowers
Darwin was happy to conduct his botanical research in his own gardens and greenhouses. A primary preoccupation of his was to try to understand why many plant species had two different reproductive forms, also known as dimorphism, or heterostyly. Dimorphism entailed one form having a short stigma and long stamens, and the other having a long stigma and short stamens. These studies led him into a research program that lasted into the late 1870s. The research involved further work on the pollination of plants by insects, and encompassed his own crossings of different plant forms, varieties, hybrids, and even species. He wanted to understand the cause of sterility, or why two organisms could not cross with one another, thereby creating two new species. His work led to the publication of four botanical books in the 1870s alone: Insectivorous Plants (1875), The Effects of Cross and Self Fertilisation in the Vegetable Kingdom (1876), The Different Forms of Flowers on Plants of the Same Species (1877), and The Power of Movement in Plants (1880).
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Otto Wilhelm Thomé. Flora von Deutschland, Osterreich und der Schweiz. Berlin: H. Bermühler, 1903-1905. [zoom] | Additional images:  "View a larger image")
Darwin crossed different forms of the primrose species, the cowslip (Primula veris). These flowers were dimorphic, or heterostyled. His research revealed that the short-styled flowers were far more fertile when an insect carried pollen to them from the stamens of the long-styled flowers. In turn, the long-styled flowers were more reproductive when crossed with the short-styled flowers than with their own form. |
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Charles Darwin. The Collected Papers of Charles Darwin. Chicago: University of Chicago Press, 1977. Vol. 2. [zoom] Some plant species included three different forms, as illustrated by Darwin’s crossing diagram in his paper on Lythrum salicaria, the purple loosestrife. |
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Purple Loosestrife (Lythrum salicaria). [zoom] Darwin crossed countless numbers of the trimorphic purple loosestrife, a plant known to North Americans as a troublesome alien invasive. This specimen was collected at the south end of Cayuga Lake in Central New York State in 1875 not long after the plant had been introduced from Eurasia. On loan from L.H. Bailey Hortorium Herbarium, Cornell University. |
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Christian Konrad Sprengel. Das entdeckte Geheimniss der Natur im Bau und in der Befruchtung der Blumen. Berlin: bei Friedrich Vieweg dem aeltern, 1793. [zoom] The German naturalist and theologian Christian Konrad Sprengel (1750-1816) was one of the few naturalists before Darwin who studied the reproductive structure of flowers in relation to their pollination by insects. Darwin often referred to Sprengel’s work in his botanical publications. |
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Charles Darwin. The Different Forms of Flowers on Plants of the same species. London: J. Murray, 1877. First edition. [zoom] Darwin noted the help of his son, William, in collecting data on the dimorphic (heterostyled) Pulmonaria angustifolia (lungwort). |
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Joseph Dalton Hooker (1817-1911). [zoom] The botanist Joseph Dalton Hooker (1817-1911), one of Darwin’s closest friends, became the Director of the Royal Botanic Gardens, Kew in 1865. Portrait from Gardeners Chronicle & New Horticulturist. London: Haymarket Publishing, 1871. |