How Domestic Varieties Originate 251 



vary and pass out of existence even though it is propa- 

 gated wholly asexually or by buds. There are to-day 

 several different types of Rhode Island Greening apple in 

 cultivation which have probably originated from varia- 

 tions induced by environment and by the different ideals 

 of propagators ; and the same is true in other fruits. 



All the foregoing remarks illustrate the importance 

 of constant attention to selection if 

 one desires to maintain the exact 

 type of any variety which he has 

 produced. They explain the value 

 of the "roguing" or systematic 

 destruction of all "rogues" or non- 

 typical plants which is invariably 

 practiced by all good seed growers. 

 But they still more emphatically 

 show that every variety is essen- 

 tially unstable, and that the only 

 abiding result is constant evolution, 

 the old forms being left behind as 

 the type expands into new and 

 better forms. Varieties to be valu- 

 able, therefore, ought not to be rigidly fixed, and, for- 

 tunately, nature has prescribed that they cannot be. 

 Probably every ten years sees a marked change in every 

 variety of any annual species which is propagated ex- 

 clusively from seeds, and every century must see a like 

 change in the tree fruits. These changes are so gradual 

 and the original basis of comparison fades away so com- 

 pletely that we generally fail to recognize the evolution. 



15. Itr is evident, therefore, that the most abiding 



FIG. 67. Pompon anem- 

 one chrysanthemum. 



