220 Retrograde Varieties 



It emerges from concealment only very rarely 

 and only on its own initiative. Such instances 

 of atavism have been described in previous lec- 

 tures, and their existence has been proved be- 

 yond doubt. 



Systematic latency explains the innumerable 

 instances in which species are seen to lack def- 

 inite characteristics which ordinarily do not 

 fail, either in plants at large, or in the group 

 or family to which the plant belongs. If we 

 take for instance the broom-rape or Orobanche, 

 or some other pale parasite, we explain their 

 occurrence in families of plants with green 

 leaves, by the loss of the leaves and of the green 

 color. But evidently this loss is not a true one, 

 but only the latency of those characters. 

 And even this latency is not a complete one, as 

 little scales remind us of the leaves, and traces 

 of chlorophyll still exist in the tissues. Nu- 

 merous other cases will present themselves to 

 every practical botanist. 



Taking for granted that characters, having 

 once been acquired, may become latent, and that 

 this process is of universal occurrence through- 

 out the whole vegetable and animal kingdom, we 

 may now come to a more precise and clear con- 

 ception of the existing differences between spe- 

 cies and varieties. 



For this purpose we must take a somewhat 



