THE SELF-FERTILIZATION OF PLANTS. 371 



in a varietal type which is of defective structure, be- 

 come of lessened fertility, and of lessened vigor. 

 These, man, for obvious reasons, rejects; and selects 

 those which are hardier and most fertile. The latter 

 owe this vigor and fertility to such slight successive in- 

 crements of growth in various parts, that the change 

 escapes man's eyes, until he awakes, with surprise, to 

 the fact of how different the variety is, to what it was 

 but a few years back ! He himself has occasioned it, 

 by his selection of the strongest and most fertile. 

 Then ; it is very difficult to confine a plant to a given 

 type, when its seed is distributed and grown in many 

 places, where the supplies of the conditions of growth, 

 are so different. A variety is, very frequently the 

 outcome both of man's selection, and of a given set 

 of conditions. Where this set of conditions, is not 

 realized, all of man's care cannot prevent a change of 

 form, in the transplanted variety. 



• "De Candolle," says he (p. 513, Origin of Species), 

 " has fully discussed the antiquity of various races of 

 plants." 



He then speaks of old varieties of the poppy, of the 

 almond, of the cabbage, of the turnip, &c, which ex- 

 isted, many centuries back, and which are measurably 

 like the varieties existing at the present day. 



"But," says he, "it does not seem improbable, that 

 some of these varieties may have been lost and reap- 

 peared;" and "whether any of these plants are abso- 

 lutely identical with our present sub-varieties, is not 

 certain." 



Respecting the changes of form, which are required 



