THE SELF-FERTILIZATION OF PLANTS. 365 



and making thoroughly available, the ingredient first 

 mentioned, which may or may not be present only in 

 meagre quantities, in its new location. It is therefore, 

 to be expected, that good will be derived from slight 

 changes in the conditions of life. 



Under the heading of " On the Good derived from 

 slight Changes in the Condition of Life" (p. 178, Vol. 

 ii, Animals and Plants, &c), Darwin says : 



"In considering whether any facts were known, 

 which might throw light on the conclusion arrived at 

 in the last chapter, namely, that benefits ensue from 

 crossing, and that it is a law of nature that all organic 

 beings should occasionally cross, it appeared to me 

 probable, that the good, derived from slight changes 

 in the conditions of life, from being an analogous phe- 

 nomenon might serve this purpose. No two individu- 

 als, and still less no two varieties are absolutely alike, 

 in constitution and structure; and when the germ of 

 one is fertilized by the male element of another, we 

 may believe that it is acted on in a somewhat similar 

 manner as an individual, when exposed to slightly 

 changed conditions. Now, every one must have ob- 

 served the remarkable influence on convalescents, of a 

 change of residence, and no medical man doubts the 

 truth of this fact. Small farmers, who hold but little 

 land, are convinced that their cattle derive great benefit 

 from a change of pasture. In the case of plants, the 

 evidence is strong that a great advantage is derived 

 from exchanging seeds, tubers, bulbs, and cuttings, 

 from one soil or place to another as different as pos- 

 sible. 



"The belief that plants are thus benefited, whether 

 or not well founded, has been frequently maintained 

 from the time of Columella, who wrote shortly after 



