ATKINSON— TWIN HYBRIDS. 135 



lamarckiana character in its rosettes, appears also to have the mutat- 

 ing constitution of lamarckiana. 



The Fn rosette of the lamarckiana type {pycno X lani.) — The 

 comolex of characters expressed in the rosette, derived from both 

 parents, are such that it resembles neither parent. Still the pre- 

 ponderance of characters expressed in the rosette of the lamarckiana 

 type of twin comes from pycnocarpa. These are the narrow, fur- 

 rowed, noncrinkled, repand leaves, while the edge character comes 

 from lamarckiana. The leaves are light green. It is a striking 

 rosette and the uniformity throughout the entire row was remark- 

 able (see Fig. 2, PI. I). 



The Fn rosette of the lamarckiana type of the reciprocal cross 

 {lam y( pycno). — Its resemblance to the rosette of the lamarckiana 

 type of pycno X ^aw is remarkable. The only observable difference 

 is that there is a slight buckling of some of the leaves, a pycnocarpa 

 character. In both of these lamarckiana types the uniformity of 

 the rosettes in the row was remarkable. 



Reciprocal Crosses of Qi^nothera franciscana and pycnocarpa. 

 Cultures of 1915; Annual. 



Oenothera pycnocarpa X CE. franciscana (No. 100). — In this 

 culture there were between 170 and 180 individuals. The majority 

 reached maturity, but there were a few of the more tardy ones which 

 formed autumn rosettes. Several of the latter began stem develop- 

 ment and advanced far enough so that the rosette types could be 

 correlated with the types presented by the mature plants in which 

 the mature rosette stage was omitted. In the F^ the progeny splits 

 into two distinct types, corresponding to twin hybrids in the sense of 

 deVries. 



Pycnocarpa Type; Rosette. — The rosette of the pycnocarpa type 

 is shown in Fig. 4, PI. II., at the right. The pycnocarpa character 

 is shown in the strongly toothed, partially cut margin of the basal 

 portion of the leaves. This rosette is not so large nor so well fur- 

 nished with leaves as those of the Fo since the few plants of 1915 

 annual culture which did not form stems, were belated and did not 

 form such fully mature rosettes. 



