64 SEEDS AND FRUITS 



Concerning the cotyledon of the Grass embryo, there is some 

 dispute. Some morphologists regard the scutellum as the coty- 

 ledon, while others think that the cotyledon includes both the scu- 

 tellum and coleoptile. Although the cotyledon may include 

 other structures, the scutellum, in absorbing and supplying food 

 to the growing parts of the embryo, performs the function of a 

 cotyledon. The scutellum is a boat-shaped structure with its 

 keel-Uke portion imbedded in the endosperm. Its broad side 

 bearing the axis of the embryo is visible through the testa and 

 ovary wall. The keel-like portion is covered with speciaKzed 

 cells formed into a layer called the epithelium. The epithelium 

 secretes soluble substances called enzymes, which after diffusing 

 to the endosperm change the foods stored there into soluble 

 forms, which are then absorbed by the cotyledon and carried to 

 the plumule and radicle where they are used for growth. 



The principal food substances, 

 stored in the endosperm are starch, 

 fat, and protein. Although occur- 

 ring together in most parts of the 

 ■^ B endosperm, each substance' is 



Fig. 67. — Kernels of Com with present in a greater proportion 

 high and with low percentages of j^ g^^^g regions than in others, 

 protein. A, kernel mth high per- ^^^ ^^jj^ ^^^^^^ ^^^ ^^^^^^ ^^ 

 centage of protein. B, kernel with 



low percentage of protem. a, horny the endosperm and formmg the 

 endosperm; h, white starchy endo- aleuron layer are especially rich in 

 sperm; e, embryo. Aitei Bulletin 87 , protein, which is present in the 

 University of Illinois Agricultural f^j.^^ ^f granules and SO abundant 

 Experiment Station. ,■, , , i n i 



that the ceils appear as dense 



granular masses. The remaining endosperm, which is especially 

 rich in starch, consists of two regions. The outer region (more 

 deeply shaded) is the horny endosperm (h) and contains much 

 protein in addition to starch. The inner region (n) (with lighter 

 shading) is the starchy endosperm, which is not only much softer 

 and more granular than the horny endosperm but also contains 

 less protein. The richness ^ of the kernel in protein depends so 

 much upon the amount of horny endosperm that by cutting across 

 a kernel as shown in Figure 67, one may judge the richness of the 

 kernel in protein by observing the relative amounts of the two 

 kinds of the endosperm. Likewise, since the embryo of the ker- 



1 See Bulletins Jt4, 82, and 87, University of Illinois Agricultural Experiment 

 Station. 



