HEREDITY 



53 



by spores, gemmae, bulbs and tubers, and the artifically 

 severed buds and scions used in grafting and "slipping." 

 3. In sexual reproduction there intervene between par- 

 ents and offspring, not only the complicated reduction 

 divisions involved in the formation of the gametes, but 

 also the nuclear and cell-fusions accomplished by the union 

 of the egg and sperm in fertilization (Fig. 38). Both proc- 

 esses — the formation of the gametes, and their fusion — • 



Fic. 38. — Fertilization in the white pine {Finns Slrobus). The smaller 

 sperm-nucleus (above) is imbedded in the (larger) egg-nucleus. The fu- 

 sion of the nucleoplasms will finally become more intimate. (After 

 Professor Margaret C. Ferguson.) 



offer almost unlimited opportunities for alterations of the 

 protoplasm — especially that of the nucleus. This method 

 of reproduction, therefore, has the very greatest interest 

 and importance for the study of heredity. In the fertilized 

 egg^ are united inheritanc-es from two parents — from two 

 distinct lines of ancestry — -protoplasms (germ-plasms) with 

 two entirely different histories extending back into the 



' The fertilized egg (as Thomson has pointed out) is the inheritance, 

 and becomes, in the mature individual, the inheritor. 



