596 THE PHYSIOLOGY OF SOWING SEEDS. 
in stones into trenches properly dug for the founda- 
tion of a building, is laying those foundations. 
The seed is the foundation of the structure of 
the future plant, and the germination of that seed 
is laying the foundation of the same. It is the 
first act in the process of the economy of vege- 
tation; and therefore, like all first acts or steps— 
most essentially important. We must therefore, 
first inquire into the nature of germination, and 
the conditions required to aid and promote it, 
before we enter upon other considerations. 
Physiology teaches us that germination is the 
principle which calls forth the dormant vitality of 
a seed, and effects all those changes within it 
which are necessary for the purposes of the growth 
and developement of the seedling plant. Like an 
egg, the seed contains a vital germ within it, and 
a store of nutritive matter around that germ, to 
furnish it with all its wants till fully matured, and 
as it were, hatched, and introduced into inde- 
pendent existence. ‘The requisite external con- 
ditions to enable a seed to go properly through 
the process of germination are a proper degree of 
temperature, a sufficiency of moisture, and a free 
access of air, with exclusion from the direct action 
of light. If air be wanting all other conditions 
