Chap. XVIII. 



GOOD OF CHANGED CONDITIONS. 



145 



.CHAPTER XVIII. 



OK THE ADVANTAGES AND DISADVANTAGES OF CHANGED 

 CONDITIONS OF LIFE : STERILITY FEOM VAEIOUS CAUSES. 



ON THE GOOD DERIVED FROM SLIGHT CHANGES IN THE CONDITIONS OF LIFE — 

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

 AND IN MENAGERIES — MAMMALS, BIRDS, AND INSECTS — LOSS OF SECONDARY 

 SEXUAL CHARACTERS AND OF INSTINCTS — CAUSES OF STERILITY — STERILITY 

 OF DOMESTICATED ANIMALS FROM CHANGED CONDITIONS — SEXUAL INCOMPATI- 

 BILITY OF INDIVIDUAL ANIMALS — STERILITY OF PLANTS FROM CHANGED CONDI- 

 TIONS 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 — INCIPIENT 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 analogous phe- 

 nomenon, might serve this purpose. No two individuals, 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. 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 fanners 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. 



VOL. II. 



