6 MENDELISM chap. 



another to give rise by a process of cell division to what we 

 ordinarily term an individual with all its various attri- 

 butes and properties ; and (3) a period of dissociation 

 when the single structured gametes separate out from 

 that portion of the double structured zygote which 

 constitutes its generative gland. What is the relation 

 between gamete and zygote, between zygote and gamete ? 

 how are the properties of the zygote represented in the 

 gamete, and in what manner are they distributed from 

 the one to the other ? — these are questions which serve to 

 indicate the nature of the problem underlying the process 

 of heredity. 



Owing to their peculiar power of growth and the rela- 

 tively large size to which they attain, many of the proper- 

 ties of zygotes are appreciable by observation. The col- 

 our of an animal or of a flower, the shape of a seed, or the 

 pattern on the wings of a moth are all zygotic properties, 

 and all capable of direct estimation. It is otherwise 

 with the properties of gametes. While the difference be- 

 tween a black and a white fowl is sufficiently obvious, no 

 one by inspection can tell the difference between the egg 

 that will hatch into a black and that which will hatch 

 into a white. Nor from a mass of pollen grains can any 

 one to-day pick out those that will produce white from 

 those that will produce coloured flowers. Nevertheless, 

 we know that in spite of apparent similarity there must 

 exist fundamental differences among the gametes, even 



