Chapter CCCLXII: Letter 730: To E. Hackel

(730/1. The following extract refers to Darwin's book on "Cross and Self-Fertilisation.")

November 13th, 1875.

I am now busy in drawing up an account of ten years' experiments in the growth and fertility of plants raised from crossed and self-fertilised flowers. It is really wonderful what an effect pollen from a distinct seedling plant, which has been exposed to different conditions of life, has on the offspring in comparison with pollen from the same flower or from a distinct individual, but which has been long subjected to the same conditions. The subject bears on the very principle of life, which seems almost to require changes in the conditions.