Systematic Atavism 631 



as for instance in the aroids and the grasses. 

 Retrograde evolution is also typical in the high- 

 est and most highly differentiated family of the 

 monocotyledons, the orchids, which have but 

 one or two stamens. In the second place I have 

 had occasion more than once to assert that retro- 

 gression, though seemingly consisting in the 

 disappearance of some quality, need not, as a 

 rule, be considered as a complete loss. Quite on 

 the contrary, it is very probable that real losses 

 are extremely rare, if not wholly lacking. Ordi- 

 narily the loss is only apparent, the capacity 

 becomes inactive only, but is not destroyed. The 

 character has become latent, as it is commonly 

 stated, and therefore may return to activity and 

 to the full display of its peculiarity, whenever 

 occasion offers. 



Such a return to activity was formerly called 

 atavism. But as we have seen, when dealing 

 with the phenomena of latency at large, sundry 

 eases of latency are to be distinguished, in order 

 to get a clear insight into these difficult proc- 

 esses. 



So it is with atavism, too. If any plant re- 

 verts to a known ancestor, we have a positive 

 and simple case. But ancestors with alternate 

 specific marks are as a rule neither historically 

 nor experimentally manifest. They are only 

 reputed to be such, and the presumption rests 



