376 THE SEED AND ITS TERMINATION 



e.g. date) — or as fats, in the form of oil drops, plant fats 

 being liquid at ordinary temperatures : the ciytoplasm 

 of the cells of the endosperm (and perisperm if present) 

 or of the embryo itself being densely packed with these 

 substances. The proportion of water in a seed is very 

 much less than in the actively growing vegetative parts 

 of the plant. 



Conditions of Germination. — So long as the ripe seed 

 is kept dry the protoplasm of its cells remains in a 

 dormant condition. Seeds may remain alive in this 

 condition for many years, and though the germination 

 of " mummy wheat " has not been verified, such an 

 occurrence is not by any means out of the question. 

 Seeds have been known to germinate after keeping 

 dry for a century, though some seeds die within a 

 comparatively short time. 



The first requisite for germination is liquid water 

 Some ripe seeds (e.g. acorns) contain enough water to 

 germinate at once if evaporation is checked by keeping 

 them in saturated air, but once they have lost a certain 

 proportion of their water they must have more supplied 

 to them from outside in order to germinate. ' The 

 second requisite is free oxygen. The living cells of the 

 embryo must be able to respire in order to liberate 

 the energy necessary for growth ; and both water and 

 oxygen are necessary to the chemical changes which 

 precede and accompany germination. The third is 

 a suitable temperature. At or below o° C. protoplasm is 

 inactive, and germination cannot occur any more than 

 can the growth processes of an ordinary growing plant. 

 Above this temperature the chemical changes on which 

 germination depends takes place more and more* quickly, 

 so that the higher the temperature, up to a certain point, 

 the more rapid germination will be. But above a 



