HEREDITY 



material is supplied. The second or extra dose 

 is, however, not superfluous. It probably adds 

 to the vigor of the organism produced, and in 

 some cases at least, materially affects its form. 

 For many animals and plants exist in two 

 different conditions, in one of which the nu- 

 clear components are simple, N, while in the 

 other they are double, 2 N. Thus in bees, 

 rotifers, and small Crustacea the egg may 

 under certain conditions develop without being 

 fertilized. If the egg develops before matura- 

 tion is complete, that is in the 2N condition, 

 the animal produced is a female, like the 

 mother which produced the egg. But if the 

 egg undergoes reduction to the N condition 

 before beginning its development, then it pro- 

 duces a male individual, an organism, so far 

 as reproduction is concerned, of lower meta- 

 bolic activity. 



In many plants, too, individuals of N and 

 of 2 N constitution occur, which differ markedly 

 in appearance. Thus the ordinary fern-plant 

 is a 2 N individual, but it never produces 2 N 

 offspring. Fig. 6 shows an ordinary fern- 

 plant, which produces spores on the under 



20 



