7 



156 Retrograde Varieties 



They are generally called atavists or rever- 

 sionists, but even these terms are sometimes 

 used in a different sense. 



Lastly it is to be said that the empirical and 

 experimental evidence as to the question of con- 

 stancy is not as extensive as it should be. The 

 experimental conditions are seldom described, 

 and it is only recently that an interest in the 

 matter has been awakened. Much remains to 

 be done. Among other things the innumerable 

 varieties of trees, shrubs and perennial herbs 

 should be tested as to their constancy when 

 grown from purely fertilized seeds. Many of 

 them may be included among the number that 

 sport constantly. 



Leaving aside the doubtful or insufficiently 

 studied cases, we may now turn our attention to 

 the facts that prove the absolute stability of 

 a large number of varieties, at least as far as 

 such completeness can be attained by experi- 

 ment or observation. 



The best proof is afforded by the varieties 

 which grow wild in localities where they are 

 quite isolated from the species, and where for 

 this reason, no possibility of crossing disturbs 

 the significance of the proof. As one instance 

 the rayless form of the wild camomile, or the 

 Matricaria Chamomilla discoidea may be men- 

 tioned. Many systematists have been so strong- 



