114 Sliull. 



of the bursa-pastoris plants of the Fs will gixe agaiu the 15 : 1 ratio 

 in the Fo from a new cross with Heegcri, thoug-h seven of them will 

 continue to breed true, indefinitely, as long- as thej- are selfed. Only 

 by crossing can the differences among these seven be discovered. 



As crossing the Bursas is a rather tedious process, aud the 

 results from selfing the hybrids during these five generations have so 

 abundantly demonstrated the method of inheritance of the triangular 

 capsule, I have made no attempt to analyze the extracted dominants, 

 l>ut a new cross made for another purpose has incidentally given proof 

 of the central fact to be exjjected from such an analysis, namely, that 

 the extracted dominants are not all identical with the original dominant 

 parent in their hereditary behavior. As already indicated, the most 

 satisfactory- method of testing these various extracted dominants is to 

 make new crosses between them and the recessive Heegcri. Certain 

 crosses among the extracted dominants themselves would also yield very 

 characteristic results, as, for instance, a cross between CCdd and ccDD, 

 which would produce the original Fi genotype and j-ield 15 : 1 in the 

 Fs. When crossed \\ith Heegcri the extracted dominants from the 

 original Fa should all yield uniform Fi progenies of B. bursa-pastoris, 

 of course, but among every seven extracted dominant plants from the 

 Fa of the original cross, 



1 (CCDD) should yield only 15:1 ratios in the new Fa faniiUes; 



' should yield 15 : I in half of the new F-. families 



4. and I I * 



\(9 rrni i I ^"'^ '^ ■ ^ i^^^i"^ i" '^I'^' "tlier half; aud 



j (CCdd) 



9 and 



" 7w^ 1 I cross. 



In crosses between £. Hecgeri and extracted B. hursa-pasforis plants 

 from the F» aud later generations of the original cross, the same 

 distribution of dominant aiul recessive types as represented in the tabu- 

 lation just given, would apjiear only when the extracted dominants used 

 in the new crosses were themselves included in a fauiily having a 15 : 1 

 ratio. In families of whatever generation, showing the 3 : 1 ratio, the 

 extracted dominants could be of but one tyi)e in any given family; 

 they must be either CCdd or ecDJ) and these in new crosses with 

 Hecgeri would yield only the monohybrid ratio 3 : 1. 



In 1911 a cross was made between an extracted Bursa Heegeri 

 simpAcx and an extracted B. bursa-pastoris heteris, the latter being 



I should yield only 3 : 1 ratios in the Fa of the new 



