After the publication of On the Origin of Species in 1859 Darwin became fascinated with the potential for botanical experiments to provide evidence for the process of evolution. First published in 1877 this volume is based on a series of papers concerning heterostylous plants (species which produce different types of flowers) originally published in the Journal of the Proceedings of the Linnaen Society in 1862. Linnaeus had divided the sexual relations of flowers into four groups which Darwin uses as the structure for this volume. Darwin examines in detail plants which produce different flower forms presenting his conclusions in terms of adaptive evolution and so providing the first functional interpretation of heterostyly. He demonstrates that these plants are adapted for cross-fertilisation not self-fertilisation as was widely believed. The concepts which Darwin introduces in this volume continue to provide the basis for research into plant reproductive biology.