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. 



THE NUTRITION OF THE SEEDLING. 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 Nutrition 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- 1 

 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 



O 



above mentioned. So far as these changes have been 

 traced, they are as follows : 



Solution of Jfiits. 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 albumiuoidf 



