506 Our Surroundings 



The Bean. In studying a bean, observe the surface markings 

 on the testa, or outer layer of the seed coat, the hilum, or scar, on 

 one side, the micropyle, or tiny opening in the hilum, and the 

 integument, or thin inner coat. Notice that the bean is composed 

 mainly of two parts of equal size and appearance. These are the 

 cotyledons, or seed leaves, in which is stored the food for the use 

 of the young plant, called a seedling, as soon as it emerges from 

 the seed. It is said to be a seedling as long as it derives its food 

 from the cotyledons, or until it has developed roots and leaves to 

 aid in the manufacture of food. Taking apart the two cotyledons, 

 observe a tiny body. The rod-like portion which is joined to the 

 cotyledons is the hypocotyl, the lower part of which will push its 

 way through the seed coat at the micropyle as the embryo grows, 

 and form the root. Attached to the upper end of the hypocotyl 

 observe a minute stem with a pair of tiny leaves. This is the 

 plumule, which will develop into the stem and leaves above the 

 hypocotyl. 



In the process of germination the stem part of the hypocotyl 

 becomes curved, forming a loop, and grows upward into the air, 

 while the root part grows downward into the soil. It is the loop 

 which breaks the way through the soil and as it grows pulls the 

 cotyledons from the soil, thus enabling the delicate plumule which 

 lies between the cotyledons to get above giound without injury. 

 Once above ground it grows rapidly, feeding upon the nutrient in 

 the cotyledons, which soon shrivel and fall away as the young 

 leaves develop. 



As the bean plant matures the plumule develops into a pair 

 of broad leaves to carry on photosynthesis, the hypocotyl becomes 

 a sturdy supporting stem, and the root develops tiny, hairlike 

 branches which take moisture and nourishment from the soil by 

 osmosis and pass them on to the rest of the plant. The seedling 

 has now become a fully developed bean plant. 



The Corn. In the study of the corn grain, or kernel, ob- 

 serve that it is somewhat wedge-shaped in form with a shallow 

 groove upon one side, underneath the surface of which the 

 embryo is visible in outline. Notice the point of attachment 

 to the cob at the lower end of the grain and the slight scar at 



