Stability and Real Atavism 157 



ly impressed with its absolute constancy and its 

 behavior as an ordinary species, that they have 

 elevated it, as it is called, to the rank of a spe- 

 cies. As such it is described under the name of 

 Matricaria discoidea DC. It is remarkable 

 for its rapid and widespread distribution, as of 

 late years it has become naturalized in different 

 parts of America and of Europe, where it is to 

 be seen especially in France and in Norway. 

 Experimentally I raised in succeeding years be- 

 tween 1000 and 2000 seedlings, but observed no 

 trace of reversion, either in the strongest or in 

 the numerous very small and weak individuals 

 which appeared in the cultures. 



The tansy-ragwort or Senecio Jacobaea may 

 be chosen as a second instance. It is a per- 

 ennial herb with short rootstocks and stout 

 stems bearing numerous short-peduncled heads 

 in a large compact corymb; it multiplies itself 

 abundantly by seeds and is very common on 

 the sand dunes of Holland. It has two forms, 

 differing only in the occurrence or the lack of 

 the ray florets. But these two varieties occupy 

 different localities and are even limited to dif- 

 ferent provinces. As far as I have been able to 

 ascertain on numerous excursions during a 

 series of years, they never sport, and are only 

 intermingled on the outskirts of their habitats. 

 The rayless form is generally considered as the 



