Non-Mendelian Inheritance loi 



zonale) described by Baxter (i). Since that time, 

 however, many more cases have been discovered, and 

 the fact of somatic segregation has become fairly well 

 established. 



An illustration of the situation may be given as 

 follows. If a white-leaved plant and a normal green- 

 leaved plant are crossed the resulting hybrid illustrates 

 what has been mentioned as "particulate inheritance," 

 that is. the hybrid is variegated, showing irregular 

 patches of white and green. If one of these white 

 patches completely includes a bud there will probably 

 be produced by that bud a completely white branch. 

 The flowers of this branch, when self-fertilized, give rise 

 through their seeds to white individuals only and would 

 evidently continue to breed true to the white condition 

 if white individuals could be matured. In like manner 

 the variegated hybrid may give rise to a pure green 

 branch, which would start a line of pure green indi- 

 viduals. 



This is an illustration of what is called "somatic 

 segregation." Ordinarily, of course, factors are segre- 

 gated only at the reduction division, and only in that 

 division does the proper cytological mechanism for seg- 

 regation exist. Somatic segregation, however, means I 

 that segregation takes place in the somatic tissue, quite 

 apart from the usual reduction division. Cytologists 

 assure us that cell divisions in the somatic tissue are not 

 reduction divisions, in this tissue chromosomes being 

 regularly reproduced in equal numbers. Each chromo- 

 some divides to form two chromosomes, and these two 

 are similar to the mother and to one another; therefore 

 they carry exactly the same quota of determiners, that is. 



