HOW CHARACTERS ARE TRANSMITTED 125 



bearing both silk and tassel and producing both ovules and pol- 

 len grains, each new kernel being independent of its neighbors. 



Fertilization in general. 

 This, roughly speaking, is 

 characteristic of fertilization 

 in general, whether plant or 

 animal. A small male cell 

 (the pollen grain in plants or 

 the spermatozoon in animals) 

 meets and fuses with the 

 larger^ female cell (ovule in 

 plants or ovum in animals), 

 which is thereafter capable 

 of developing into a new in- 

 dividual possessed of all the 

 characters of both parents. 



The method of effecting 

 this union of the nuclei in 

 fertilization and the time at 

 which it takes place vary 

 greatly in different species. 

 In many plants both sex cells 

 are borne by the same indi- 

 vidual, either in one flower, 

 as in the apple and the elm, 



or in separate flowers, as in corn.^ In others, as the chestnut and 

 the box elder, the male flowers are borne on one plant and the 



* Though the female cell is always larger than the male, the nucleus, which 

 •cems to be the essential part, has the same number of chromosomes (see 

 chromosomes), so that the male and the female parents have identical powers 

 in transmission. The differences in size are apparently due to the amount of 

 protoplasm surrounding the nucleus, probably as food material for the develop- 

 ing young and in no way connected with heredity. This difference is some- 

 times great, as in the egg of the hen, most of which is food material for the 

 developing chick, while the male cell is microscopic. 



2 This bisexuality, or hermaphroditism, is also found in certain lower animals, 

 as the earthworm. 



Fig. 19. Kernels of corn growing on 



the tip of the tassel ; occasional but 



not common 



