ATKINSON— TWIN HYBRIDS. 131 



tember. A very few of the plants did not pass beyond the rosette 

 stage, and as there were a number in which stem development began 

 late in the season, it was possible to connect the types of rosettes 

 with the types of mature plants. 



Reciprocal Crosses of CEnothera lamarckiana and pycnocarpa. 

 Cultures of 1915, Annual. 



CEnotliera lamarckianay^OB. pycnocarpa (No. pp). — Including 

 those individuals which did not advance beyond the rosette stage 

 there were between 80 and 90 plants in the F^. There was a dis- 

 tinct splitting into two types, i. e., twin hybrids were formed. In 

 certain respects these twin hybrids agree with twin hybrids obtained 

 by de Vries (1913) in crosses of CE. lamarckiana with certain other 

 species. In certain characters they nesemble one of the parents but 

 are modified by the other parent. I shall speak of them as the pyc- 

 nocarpa type and the lamarckiana type, but there are such a number 

 of strong contrast characters in the two species that the names of 

 the types might wnth equal reason be reversed, depending on the 

 form character chosen to represent the type. In this case the 

 deeply cut feature of the rosette leaves, present in pycnocarpa, serves 

 to mark the pycnocarpa type, while the nearly plain, or slightly 

 toothed feature of the rosette leaves of lamarckiana serves to indi- 

 cate the lamarckiana type. 



Pycnocarpa Type; Rosettes.^A rosette of this type obtained in 

 the 191 5 cultures is represented in Fig. i, PI. i. The pycnocarpa 

 character, cutness of the basal half of the leaves is clearly seen, 

 though they are not so deeply cut as in the rosette leaves of the 

 parent (see Atkinson, 191 7, p. 228, Fig. 13). The rosette is strongly 

 modified, however, by the lamarckiana characters, convexity and 

 crinkledness of the leaves, and the leaves are a little broader than 

 those of pycnocarpa. 



Pycnocarpa Type; Mature Plant. — There were 54 mature plants 

 of this type in the culture. The width and edge character of the 

 leaves come from pycnocarpa. They are long, narrow, more or less 

 furrowed, and rather strongly toothed, more so over the base, as in 

 pycnocarpa. The leaves are rather crowded and drooping, but are 



