80 Plant-Breeding 



ous that they seem to be quite regular. The peloric 

 type is known to have originated from the ordinary type 

 at different times and in different countries, under more 

 or less divergent conditions. 



White varieties of many species of bluebells, gentians, 

 and nearly all of the berry-bearing species in the large 

 heather family are quite common. The same is true of 

 the white flowers of Brunella vulgaris, Ononis repens, and 

 Thymus vulgaris. 



Spontaneous occurrence of new elementary species in the 

 wild state. It will be. remembered that new elementary 

 species of the CEnothera were found to occur in the wild 

 state before any attempt was made to study them under 

 cultivation. It is difficult to say how frequently these 

 mutations occurred in the wild because unquestionably 

 most of them were destroyed prematurely, from the com- 

 petition of other plants. 



The occurrence of new elementary species in the wild 

 state seems to be much more rare than the occurrence of 

 new varieties. This is natural, for, of course, elementary 

 species present greater differences from the parental 

 forms than do varieties. 



The spontaneous origin of the new elementary species, 

 Capsella Heegeri, in 1897, has never been observed to have 

 been repeated since that time. 1 This new form of shep- 

 herd's purse originated in the market-place near Landau, 

 in Germany. 



Spontaneous occurrence of new elementary species and 

 varieties under cultivation. Whenever new forms occur 

 spontaneously under cultivation, it should first be deter- 



1 De Vries, " Species and Varieties, their Origin by Mutation," p. 582. 



