648 Mutations 



comes as prominent as it must once have been in 

 the ancestors, and is still in that part of their 

 offspring, which has not become changed in this 

 respect. Thus the proof of our assertion of 

 systematic atavism is, in this case, not obtained 

 by the inspection of the adult, but by the investi- 

 gation of the conditions in an early stage. 

 It remains to be explained how the twisting may 

 finally be caused by this incipient grouping of 

 the leaves. Before doing so, it may be as well 

 to state that the case of the teasel is not an iso- 

 lated one, and that the same conclusions are 

 supported by the valerian, and a large num- 

 ber of other examples. In early spring some 

 rosettes show a special condition of the 

 leaves, indicating thereby at once their atavism 

 and their tendency to become twisted as soon 

 as they begin to expand. The Sweet William 

 or DiantJius barbatus affords another instance; 

 it is very interesting because a twisted race 

 is available, which may produce thousands of 

 instances developed in all imaginable degrees, 

 in a single lot of plants. Viscaria oculata 

 is another instance belonging to the same fam- 



iiy. 



The bedstraw (Galium) also includes many 

 species which from time to time produce twist- 

 ed stems. I have found them myself in Holland 

 on Galium verum and G. Aparine. Both seem 



