The Different Forms of Flowers on Plants of the Same Species was published by John Murray in 1877. The book investigates a phenomenon that had puzzled botanists: why do some plant species produce two or even three distinct forms of flowers, differing in the relative lengths of their stamens and pistils? Primroses, for example, produce “pin” flowers (with a long pistil and short stamens) and “thrum” flowers (with a short pistil and long stamens). Darwin demonstrated that these different forms are adaptations to ensure cross-pollination — pin flowers are most successfully pollinated by pollen from thrum flowers, and vice versa.
Darwin’s experiments were meticulous. He hand-pollinated thousands of flowers, counted seeds, measured pollen grains, and tracked the fertility of different crosses over multiple generations. The results were clear: “legitimate” crosses (pin x thrum) produced more seeds and more vigorous offspring than “illegitimate” crosses (pin x pin or thrum x thrum). The different flower forms, far from being random variations, were evolved mechanisms for promoting genetic diversity through outcrossing.
The book extends its analysis to trimorphic species (like purple loosestrife, which produces three flower forms) and to plants with cleistogamous flowers (flowers that never open and are self-fertilized). In each case, Darwin showed that the floral structure could be explained as an adaptation shaped by natural selection.
First edition (John Murray, London, 1877): Green cloth binding.
Market values:
- First edition, fine: $800–$2,000
- Very good: $300–$800