222 BOTANY: PRINCIPLES AND PROBLEMS 



heterozygous in one or both factor pairs and so will not breed 

 true to their present appearance. The only F2 individuals which 

 will persist unchanged when inbred are those which are com- 

 pletelj^ homozygous. 



Fig. 127. — A mutation in tobacco. The Stewart Cuban variety, which pro- 

 duces an unusually large number of leaves per plant. {From the Journal of 

 Heredity) . 



Such, in brief, are the essential features of "Mendehsm". 

 The intensive research of the past twenty years in the fields of 

 both botany and zoology has shown that conditions in many 



