6 VII. INTERNATIONAL ZOOLOGICAL CONGRESS 



a series of elementary species in the former corresponding with those 

 in the latter species. 



(3) The leaf characters are inherited in strict Mendelian ratios, 

 but the capsule shows a very great departure. The bursa-pastoris 

 capsule dominates the F 1 generation, but the heegeri capsule appears 

 in the F 2 generation, in only 1 in 18 to 25 individuals. 



(4) Under these circumstances the capacity of B. heegeri for self- 

 maintenance in competition with B. bursa-pastoris rests upon the 

 comparative infrequency of cross-fertilization. 



My sincere thanks are hereby tendered to Dr. E. N. Transeau in 

 whose charge these cultures were left during my absence in Cali- 

 fornia. A large part of the work of grouping the F 2 into the proper 

 classes was done by him. 



