THE NATURE OF SEEDS 



341 



hole made with the point of a needle. The nucellus dis- 

 appears. Its place is taken by the tissue called endosperm, 

 or, in the absence of endosperm, by the enlarged cotyle- 

 dons. (See page 66.) Cotyledons are sometimes called 

 seed leaves. At first they do not have the appearance of 



%.. 





A B C 



Fig. 149. — Diagrams of lengthwise sections of the seeds of rice, wheat, and corn, 

 the three most important sources of the food of man. A , rice ; a, the seed coat ; 

 b, the aleurone (protein) layer of the endosperm; c, the starchy part of the en- 

 dosperm; d, the embryo. B, wheat; k, the embryo; a, the gluten (protein) 

 layer; t, layers of the husk which is partly pericarp and partly testa; i, the 

 starchy part of the endosperm. C, corn; c, the seed coat; e, the aleurone (pro- 

 tein) part of the endosperm ; eg, the yellowish, hard part of the endosperm which 

 contains both protein and starch ; sw, the whitish, starchy part of the endosperm ; 

 the region which contains the embryo is rich in both oil and proteins ; the cotyle- 

 don is extended into a branched, absorbing organ, sc; s, the plumule; w, the 

 radicle. 



true leaves, but, as to origin, they are leaves, the first leaves 

 of the embryo. In some cases the cotyledons, after ger- 

 mination, turn green and manufacture food for the seed- 

 ling, as well as contributing that which was manufactured 

 in the parent plant and stored in them. (A seedling is a 

 young plant which is still drawing nourishment from the 



