318 HOW CROPS GROW. 
supply of air, and warmth; but the kind of weather, 
which determines both temperature and degree of moist- 
ure, have their effect upon the time of germination, and 
since these conditions are so variable, the rules of practice 
are laid down, and must be received with, a certain latitude. 
§ 4, 
THE CHEMICAL PHYSIOLOGY OF GERMINATION. 
Tux Norririon or tae Srepiinc.—The young plant 
grows at first exclusively at the expense of the seed. It 
may be aptly compared to the suckling animal, which, 
when new-born, is incapable of providing its own nourish- 
ment, but depends upon the milk of its mother. 
The Nuftrition of the Seedling falls into three processes, 
which, though distinct in character, proceed simultaneous- 
ly. These are, 1, Solution of the Nutritive Matters of 
the Cotyledons or Endosperm ; 2, Transfer ; and 3, As- 
similation of the same. 
1, The Act of Solution has no difficulty in case of dex- 
trin, gum, the sugars, albumin, and casein. The water 
which the seed imbibes to the extent of one-fourth to 
five-fourths of its weight, at once dissolves them. 
It is otherwise with the fats or oils, with starch and 
with gluten, which, as such, are nearly or altogether insol- 
uble in water. In the act of germination provision is 
made for transforming these bodies into the soluble ones 
above mentioned. So far as these changes have been 
traced, they are as follows: 
Solution of Fats.—Sachs has recently found that squash- 
seeds, which, when ripe, contain no starch, sugar, or dex- 
trin, but are very rich in oil (50°|,,) and albuminoids 
