The Effects of Cross and Self Fertilisation in the Vegetable Kingdom is a book on evolution in plants by Charles Darwin, first published in 1876.
In this book Darwin examines the effects of cross and self fertilisation of plants and provides experimental evidence for a hypothesis stated in his famed book of 1859, Origin of Species, that "... in none [i.e. plant] [...]can self-fertilisation go on for perpetuity" (Origin, p. 101).
He reports on experiments conducted on over 60 different species of plants, where he used controlled pollinations in order to produce self-fertilised and cross-fertilised descendants.
Thus he showed that inbreeding may have severe detrimental effects on progeny.
This book has remained the starting point for the study of inbreeding and is cited in scientific papers to this effect to this day.