The Anatomy and Physiology of Plants 65 



a corn field and tearing off tlie roots that were feeding 

 the plants. 



But to return to our beans. Note the beans planted in 

 the box of moist sand. The two halves of the bean sepa- 

 rate as they come above the soil. They get larger, and 

 green in color, and the little leaves that you saw in embryo 

 in the split bean are developing into large green leaves. 

 Until the plant takes on this green color it is entirely 

 dependent for food on what was stored in the dry bean. 

 The two halves, separating, form the cotyledons or seed 

 leaves, though they never take on the character of true 

 leaves, and it is not necessary they should in the bean 

 because of the rapidity with which the second pair of 

 leaves come out. But the thick cotyledons could remain 

 under ground and feed the plant till the true leaves appear. 

 In fact this is done by the garden pea and the acorn, the 

 cotyledons of which always remain below ground, and the 

 first leaves seen are the true leaves and not seed leaves. 



The green color is caused by certain granules in the 

 living matter of the cells taking on a green color. These 

 granules are called chlorophyll grains, and the green color 

 they carry is the most important thing in the life of the 

 higher-developed plants, as we shall see later. The httle 

 bean, now having roots, a pair of seed leaves, and a second 

 joint and pair of leaves, is a complete plant, and has all 

 the parts that any plant has, even to the largest tree; for 

 the great tree is but a repetition of these plant units: a 

 node or joint, an internode or space between the joints, 

 and a pair of leaves or one leaf. The bean plant in the 

 sand has these, and the great tree merely has more in 

 number of the same things. 



