OESMIMATIOir. 351 



the soil. The plumule ascends into the atmosphere and 

 seeks exposure to the direct light of the sun. 



The endosperm, if the seed have one, and in many 

 cases the cotyledons (so with the horse-bean, pea, maize, 

 and barley), remain in the place where the seed was 

 deposited. In other cases (kidney-bean, buckwheat, 

 squash, radish, etc.) the cotyledons aecend and become 

 the first pair of leaves. 



The ascending plumule shortly unfolds new leaves, 

 and, if coming from ihe seed of a branched plant, lateral 

 buds make theii- appearance. The radicle divides and 

 subdivides in beginning the issue of true roots. 



When the plantlet ceases to, derive nourishment from 

 the mother-seed the process is finished. 



§3. 



THE CONDITIONS OF GEKMINATION. 



As to- the Conditions of Germination we have to con- 

 sider in detail the. following : — 



a. Temperature. — Seeds sprout within certain more 

 or less narrow limits of warmth. 



Sachs has approximately ascertained, for various agri- 

 cultural seeds, the limits of warmth at which germina- 

 tion is possible. The lowest temperatures range from 

 below 40° to 55°, the highest, from 102° to 116°. Below 

 the minimum temperature a seed preserves its vitality, 

 above the maximum it is killed. He finds, likewise, that 

 the point at which the most rapid germination occurs is 

 intermediate between these two extremes, and lies be- 

 tween 79° and 93°. Either elevation or reduction of 

 temperature from these degrees retards the act of 

 sprouting. 



In the following table are given the special tempera- 

 tures for six common plants : " 



