318 HOW CKOPS GEOW. 



supply of air, and -warmth; but the kind of weather, 

 which determines both temperature and degree of moist- 

 ure, have their eifect upon the time of germination, and 

 since these conditions are so variable, the rules of practice 

 are laid down, and m.ust be received with, a certain latitude. 



4. 



THE CHEMICAL PHYSIOLOGY OF GERMINATION. 



The Nutrition op the Seedlijtg. — 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 nomish- 

 ment, but depends upon the milk of its mother. 



The ISTutrition 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, ^s- 

 similation of the same. 



1. The Act of Solntion 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 



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