CHAPTER X 

 DISPERSAL AND GERMINATION OF SEEDS 



102. The seed structures. There are three structures 

 to be considered in connection with the seed (Fig. 117) : 

 (1) the testa (seed-coat), which is a hard and resistant pro- 

 tective structure; (2) the endosperm, which is the tissue 

 usually containing stored food ; and (3) the embryo, which is 



FIG. 132. Section of bean with one cotyledon removed, showing the testa (the dark 

 boundary), the remaining cotyledon (filling the seed to the testa), the hypocotyl 

 (its tip directed upward), and the plumule (directed downward). 



the young plant that is to be protected and fed, and which is 

 to emerge from the seed and form a new and independent 

 plant. The testa and the embryo are always evident, but 

 sometimes the endosperm has disappeared. For example, 

 in the cereals (wheat, corn, rice, etc.) all three structures are 

 present, and the endosperm contains the starch we use for 

 food ; but in peas and beans the endosperm has disappeared, 



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