SEEDS AND SEEDLINGS 



69 



flower the same part that formed the pod of the bean with 



its contained seeds. The corn grain is a fruit and not a seed. 



Structure of a Grain of Corn. Examina- 

 tion of a well-soaked grain of corn discloses 



a difference in the two flat sides of the grain. 



A light-colored area found on one surface 



marks the position of the embryo; the rest 



of the grain contains the food supply. The 



scar marking the former attachment of the 



silk is found near the outer edge of the grain. 

 A grain cut lengthwise perpendicular to 



the flat side and then dipped in weak iodine 



shows two distinct parts, an area containing 



considerable starch, the endosperm, and the 



embryo or young plant. Careful inspection 



shows the hypocotyl and plumule (the latter 



pointing toward the free end of the grain) 



and a part surrounding them, the single coty- 

 ledon (see Figure). Here again we have an 



example of a fitting for future needs, for in 



this fruit the one seed has at hand all the 

 food material necessary for 

 rapid growth, although the 

 food is here outside the em- 

 bryo. 



Endosperm the Food Sup- 

 ply of Corn. We do not find 



that the One cotyledon of the Longitudinal section of 



corn grain serves the same 



H, hypocotyl; 

 P, plumule. 



young ear of corn : O, 

 the fruits ; S, the stig- 

 mas; SH, sheathlike 

 leaves ; ST, the flower 

 stalk or peduncle. 

 (After Sargent.) 



A grain of corn, 

 cut lengthwise : 



c, cotyledon; purpose to the young plant 

 E, endosperm; as did the two cotyledons of 

 the bean. Although we find 

 a little starch in the corn 

 cotyledon, still it is evident from our tests that the endosperm is 

 the chief source of food supply. The study of a thin section of 

 the corn grain under the compound microscope shows us that the 

 starch grains in the outer part of the endosperm are large and 

 regular in size. Those near the edge of the cotyledon are much 



