The Effects of Cross & Self-Fertilisation in the Vegetable Kingdom

In 1876, Darwin turned from observation to experiment. This book documents his meticulous study of over 60 plant species, where he manually pollinated flowers to produce self-fertilized and cross-fertilized progeny, then measured their growth side by side. The results were decisive: cross-fertilized offspring consistently outperformed their self-fertilized siblings in height, weight, and survival. Darwin provided the experimental proof for what he had only asserted in Origin of Species, that self-fertilization cannot continue indefinitely without deleterious effects. The work established the scientific foundation for understanding inbreeding depression, a concept that would later reshape plant and animal breeding, and remains cited in genetic research to this day. Written in Darwin's characteristic careful prose, this is not a book of grand theory but of patient, rigorous evidence, one of the most important experimental works in the history of biology.