SEEDS AND SEEDLINGS 



141 



After the rest period the time required for germination 

 varies greatly. 1 Grains, grasses, and many seeds of herbs of 

 the Pea family germinate in 2 to 8 days, most seeds of plants 

 of the Parsley family in about 14 days. Seeds of trees and 

 shrubs usually require much more time ; for example, those of 

 the hornbeam and ash are said 

 not to grow until the second 

 spring after they are planted. 



FIG. 130. Wheat seedling 



g, the grain ; GL, ground line ; 



s.l, sheathing leaf; I, first true 



leaf. One half natural size 



FIG. 131. Corn seedling 



g, the grain ; GL, ground line ; r, first 



root, from the tip of the embryo ; r', 



later roots; s.l, sheathing leaf. One 



half natural size 



132. Types of seedlings. Seedlings 2 may be divided into two 

 groups, monocotyledonous seedlings and dicotyledonous seedlings. 

 Those of the dicotyledonous group may be further sub-divided 

 into plants with underground cotyledons, as the pea and the oak, 



1 See Crocker, "R61e of Seed Coats in Delayed Germination," Botanical 

 Gazette 42, October, 1906. 



2 Not considering those of coniferous shrubs and trees (Fig. 256). 



