No. 568] X CAPSELLA BURSA-PASTORIS A RACHN IDEA 235 



Conclusions 



1. Besides the genes (A, B, C, D) discovered by tthull, 

 there exists in Capsella a gene N, responsible for the nar- 

 row character of the early leaves of certain forms. 



2. Absence of the gene A 7 results in the formation of 

 early leaves of a "broad" character. 



3. The form designated arachnoidal is of hybrid origin, 

 as are the forms Setchelliana, Treleaseana and attenuata. 



4. X Capsella Bursa-pastoris arachnoidca is formed 

 whenever the plant is homozygotic for N, whatever the 

 constitution of the remainder of the zygote {BBNN, 

 BbNN, bbNN), i. e., a homozygous condition for the pres- 

 ence of a single factor may overshadow the influence of 

 others. 



5. Homozygosity for a single factor may be responsible 

 for total, or almost total, sterility. 



6. A knowledge of the early stages, as well as of the 

 climax leaves, is essential for the classification of the 

 phenotypes of Capsella Bursa-pastoris. 



