SCOPE OF GENETICS 15 



absent. This last phenomenon, which is 

 called segregation, constitutes the essence of 

 Mendel's discovery. \ 



So recurring to the simile of the man as 

 made by the mixing of tinctures, the process 

 of redistribution of his characters among the 

 germ-cells may be represented as a sorting 

 back of the tinctures again into a double row 

 of bottles, a pair corresponding to each in- 

 gredient ; and each of the germ-cells as then 

 made of a drop from one or other bottle 

 of each pair : and in our model we may repre- 

 sent the phenomenon of segregation in a 

 crude way by supposing that the bottles 

 having no tincture in them, instead of being 

 empty contained an inoperative fluid, say 

 water, with which the tincture would not mix. 

 When the new germ-cells are formed, the two 

 fluids instead of diluting each other simply 

 separate again. It is this fact which entitles 

 us to speak of the purity of germ-cells. They 



