160 Plant-Breeding 



in the second and succeeding hybrid offspring of these 

 plants; the mathematical law is that each character 

 separates in each of these generations in one-fourth of the 

 progeny and thereafter remains true. In concise figures, 

 it is expressed as follows : 



1 D : 2 DR : 1 R. 



1 D and 1 R come true, but 2 DR breaks up again into 

 dominant and recessives in the ratio of 3 to 1. 



Mendel found that this law holds more or less for the 

 other characters that he studied in the pea, as well as for 

 the seed-shape. He did not conclude, however, that it 

 holds good for all plants, but left the subject for further 

 investigation. It will be seen at once that it will be a 

 very difficult matter to follow this law when many char- 

 acters are to be constrasted, particularly when the char- 

 acters are quantitative, or qualitative which grade into 

 each other. 



The dominant characters pertain to either parent. Some 

 of them may come from the seed parent and some from 

 the pollen parent. When this roundness is dominant from 

 the male parent, there can be seen the immediate effect of 

 pollen, the same as if the dominant roundness came from 

 the female parent. In the case of the pea, the seed-content 

 is embryo and we are not surprised to find this immediate 

 effect of pollen. In those plants in which the embryo 

 is embedded in endosperm, however, the effect of the cross- 

 fertilization is not seen until the seed has been planted 

 and produced a new generation. The endosperm is a part 

 of the female parent and is not ordinarily changed by the 

 process of cross-fertilization. In the case of a few plants, 



