■20U 



THE AMERICAN NATURALIST [Vol. XLVIII 



origin of the linear-leaved form which, because of its 

 striking appearance, concentrated the attention upon it- 

 self. That perhaps we were dealing with a mutation was 

 a thought which most naturally obtruded itself upon 

 the mind of one who, for years, had fruitlessly tested 

 a large number of species in the hope of discovering a 

 case analogous to that of Oenothera Lamarckiana. 10 The 

 possibility of a cross between a local form and either 

 Capsella Heegeri or C. procumbens, suggested itself. 

 However, the seedling stage of either of these two forms 

 does not bear the remotest resemblance to that of Cap- 

 sella arachnoidea. At the same time there was slight 

 reason for believing that either Capsella Heegeri or Cap- 

 sella procumbens ever had been grown in Ann Arbor. 



During 1911 and the greater part of 1912, the problem 

 rested here, no satisfactory explanation being found. 

 But pedigree cultures were continued until, on the one 

 hand, we succeeded in placing the plants in optimum sur- 

 roundings for the production of climax leaves, and on the 

 other began to distinguish between the various biotypes. 



The Biotypes 



As has been noted previously, it was possible to use two 

 criteria for the classification of the rosets. Leaving out 

 of consideration the rosets of the linear-leaved arach- 

 noidea, it was found that after dividing the rosets accord- 

 ing to the " broad" or " narrow" character of the earlier 

 leaves (Fig. 3), it was possible to further subdivide each 

 group on the basis of the marginal indentation of the 

 leaves subsequently formed. 



I. The "Broad" Group. — Here the first four or five 

 leaves possess a blade which is approximately twice as 

 long as broad. Up to this stage the margin remains 

 entire. When the sixth leaf appears one ordinarily can 

 begin to distinguish between two types. These are : 



Type 1. — In this, the first of the two broad-leaved 

 forms, the margin of the first eight leaves remains entire, 



io Hus, H., "The Origin of Species in Nature," American Nattjbalist, 

 45: 646, Nov., 1911. 



