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THE AMERICAN NATURALIST [Vol. XLVIII 



The above- descriptions apply only to plants grown 

 under fairly uniform conditions, in a light soil in a green- 

 house, and treated in such a manner as to offer the plant 

 the most favorable conditions for development. By leav- 

 ing the plants too long in the flats, so that crowding re- 

 sults, by keeping them too moist and warm, etc., it is 

 possible to produce abnormal climax leaves in which the 

 typical differences can be recognized with difficulty only. 

 By leaving plants too long in the seedpans, by keeping 

 them too dry, it may be brought about that plants flower 

 without having produced climax leaves. There will be 

 doubtless many who, because of this, will refuse recogni- 

 tion to the segregates just described. "Qusecunque dixi, 

 si placuerint, dictavit auditor." Fortunately, the differ- 

 ences of behavior on breeding are such, we must recognize 

 their distinct genotypic constitution. 



G-enotypic Constitutions 



Shull, in the papers above quoted, made one of the most 

 important of recent contributions to science, since he de- 

 termined with exactitude the relations existing between 

 some of the lesser forms which, because of their alleged 

 constancy or inconstancy, have been a bone of contention 

 since the days of Jacquin. Making extensive cultures of 

 Capsella, Shull was able to distinguish four forms (Fig. 

 10), to wit, heteris, with leaves divided to the midrib, with 



