220 PLANT LIFE 



zygote combines within itself the slightly 

 different properties borne by the egg and 

 sperm, in so far as they are of different 

 origin. This must be specially true when 

 the gametes spring from different parents, 

 for there is no doubt as to the transference, 

 by means of the gametes, of the hereditary 

 qualities of the organisms from which the 

 gametes have sprung. 



Experience teaches us that the egg and 

 sperm contribute equally towards the char- 

 acters of the plant which will develop from 

 the zygote. The reason for this almost 

 certainly lies in the preponderant share taken 

 by the nucleus in determining the organisa- 

 tion of the individual, The sperm and egg 

 contain about equal parts of the essential 

 constituents of the nucleus, and this explains 

 the circumstance that the minute sperm is as 

 potent, from the point of view of the trans- 

 mission of hereditary characters, as is the 

 bulky egg. 



These two functions, rejuvenescence and the 

 combination of diverse hereditary characters, 

 then, are the most obvious results achieved 

 by fertilisation. Probably the first-named 

 function, rejuvenescence, is the more primi- 

 tive, and the chemical affinity between the 

 egg and sperm first arose and was maintained 

 by the primitive conditions that made fertili- 

 sation a conditio sine qua non of further 

 development. But the second was inevi- 

 tably bound up with it. This latter circum- 



