6 SEEDS AND SEEDLINGS 



passes to the young growing plant. In some seeds, of which 

 corn is a good example, the only apparent function of the coty- 

 ledon is for absorption of the stored food, but in the castor bean 

 the cotyledons serve first for absorption and later as foliage. 

 In some seeds the cotyledons serve for storage only, but in others 

 they serve for storage and as the first leaves. 



The corn, bean and castor bean are most excellent types for 

 study. They are easily secured, large and easily handled, and 

 possess all the characters commonly found in seeds. They illus- 

 trate all the preceding points concerning cotyledons and food 

 supply. 



A grain of corn is flat, almost triangular in shape and has 

 a depression or groove on one side. Lying beneath this groove 

 is the little embryo plant with its root turned towards the point 

 of the grain, and the stem and cotyledon towards the large end. 

 The embryo plant is almost surrounded by the tip or endosperm 

 starch. The remainder of the grain is made up primarily of 

 starch, which is covered with a thin layer of gluten and a thin 

 membranous, horny coat. The corn is not a simple seed in the 

 same sense that the bean is a simple seed. You will recall that 

 the bean seed is removed from the pod. But the grain of corn 

 is not taken from a pod. In fact, the thin membranous horny 

 coat just referred to is the pod which adheres to the seed cover- 

 ing or seed coats. Therefore, the grain of corn, as we shall learn 

 later, is not a simple seed, but a fruit. The grain of corn con- 

 sists of the embryo plant, surrounded by the stored food and en- 

 closed in a thin membranous covering consisting of the united 

 seed coat and pod. The grains of wheat, oats and other grasses 

 possess similar characters. (Fig. 1.) The embryo consists 

 of a single cotyledon (or primary leaf), a short stem and a 

 short root. 



The seed of the bean is very different from the grain of corn. 

 The two large fleshy parts are the cotyledons and since there 

 are two of them it is a dicotyledonous seed. They are the 



