Chai\ XYIIL GOOD FROM CHANGED CONDITIONS. 127 



CHAPTER XVIII. 



ON THE ADVANTAGES AND DISADVANTAGES OF CHANGED 

 CONDITIONS OF LIFE : STERILITY FROM VARIOUS CAUSES. 



ON THE GOOD DERIVED FROM SL T £HT CHANGES IN THE CONDITIONS OF LIFE 

 — STERILITY FROM CHANGED CONDITIONS, IN ANIMALS, IN THEIR NATIVE 

 COUNTRY AND IN MENAGERIES — MAMMALS, BIRDS, AND INSECTS — LOSS OP 

 SECONDARY SEXUAL CHARACTERS AND OF INSTINCTS — CAUSES OF STERILITY 

 — STERILITY OF DOMESTICATED ANIMALS FROM CHANGED CONDITIONS — 

 SEXUAL INCOMPATIBILITY OF INDIVIDUAL ANIMALS — STERILITY OF PLANTS 

 FROM CHANGED CONDITIONS OF LIFE — CONTABESCENCE OF THE ANTHERS 

 — MONSTROSITIES AS A CAUSE OF STERILITY — DOUBLE FLOWERS — SEEDLESS 

 FRUIT — STERILITY FROM THE EXCESSIVE DEVELOPMENT OF THE ORGANS 

 Of VEGETATION — FROM LONG-CONTINUED PROPAGATION BY BUDS — IN- 

 CIPIENT STERILITY THE PRIMARY CAUSE OF DOUBLE FLOWERS AND 

 SEEDLESS FRUIT. 



On the Good derived from slight Changes in the Conditions of 

 Life. —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 analo 

 gous phenomenon, might serve this purpose. Is'o two indi- 

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

 in constitution and structure ; and when the germ of one is 

 fertilised 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. Kow, every 

 one must have observed the remarkable influence on conva- 

 lescents 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 possible. 



