142 LUTHER BURBANK 



For example, the relations of tall and short 

 peas, blended in heredity, are quite independent 

 of the question of yellowness versus greenness 

 of pod. So observation may be made as to two 

 or more qualities in the course of the same 

 experiment. 



Thus, if a tall variety of pea that bears green 

 pods is crossed with a short variety bearing 

 yellow pods, all the offspring will be tall peas 

 with yellow pods therefore unlike either parent. 

 But the offspring of the next generation will 

 such a recurrence of each of the recessive factors 

 in one case in four, so that one-fourth of them 

 will be short and one-fourth will have green 

 pods. But it appeared, so far as Mendel could 

 determine, to be a mere matter of chance like 

 the throwing of dice as to the exact number of 

 cases in which shortness of stalk would be com- 

 bined with the bearing of yellow pods. 



PAIRING THE FACTORS 



If we assume as Mendel finally came to do 

 that each of the different qualities about which 

 we are speaking is represented in the germ plasm 

 by a definite mechanical factor which must be 

 paired with another factor, either like or unlike 

 itself, in order to stimulate the development of 

 the character it represents, then at least a pro- 



