1 42 DOMESTICATED ANIMALS AND PLANTS 



the blood of a three-fourths white bred with a seven-eighths white 

 would be 5 — I, or if white with the remaining T 3 _ yellow, — 



this much for single kernels or for a whole generation of known 

 mixed breeding. 



Suppose now that white and yellow corn be planted together 

 in the same field in equal proportions. What will be the nature 

 of the crop ? The answer to this question covers one of the most 

 important points in plant or animal improvement, for there is 

 no essential difference in principle between the two, and what 

 applies to one applies equally to the other, so far as principles 

 are concerned. 



In such a field planted equally with white and yellow corn 

 the first question is, Will all the kernels be mixed ? Manifestly 

 not. Under the law of chance x a yellow silk, for example, will 

 have equal opportunities of being fertilized by a yellow or by a 

 white pollen grain ; that is to say, the ovule stands equal chances 

 of developing as a pure or as a mixed kernel, and the same may 

 be said of any kernel in the field, provided of course that the 

 number of silks and of pollen grains are equal, as was specified 

 in the problem. 



When the season is over, the whole population of corn ker- 

 nels of the field will then be as follows : on the stalks arising 

 from yellow kernels \ will be pure yellow and \ will be mixed, 

 yellow and white ; on the stalks arising from white kernels \ 

 will be pure white and \ will be mixed, yellow and white. 



Now, as the corn was planted half and half, each kind of 

 stalk represents half the crop. So we have for the field as 

 a whole, \ pure yellow ; \ mixed, white on yellow ; \ pure 

 white ; \ mixed, yellow on white. 



But as white pollen on yellow silk gives the same mixture as 

 yellow pollen on white silk, we have our population reduced to 

 the following : \ pure yellow, \ mixed, \ pure white, from which 



1 " Principles of Breeding," pp. 365, 504. 



