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-like 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 specialized 
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 
endosperm, each substance is 
Fic. 67.— Kernels of Corn with present in 2 greater proportion 
high and with low percentages of in some regions than in others. 
protein. A, kernel with high per- 
centage of protein. B, kernel with The cells around the border of 
low percentage of protein. a, horny the endosperm and forming the 
endosperm; b, white starchy endo- aleuron layer are especially rich in 
sperm; e,embryo. After Bulletin 87, protein, which is present in the 
University of Illinois Agricultural form of granules and so abundant 
Experiment Bian. that the cells 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 amount of the two 
kinds of the endosperm. Likewise, since the embryo of. the ker- 
1 See Bulletins 44, 82, and 87, University of Hlinois Agricultural Experiment 
Station. 
