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 quad non of further 
development. But the second was inevi- 
tably bound up with it. This latter circum- 
