264 



TYPICAL FLOWERING PLANTS 



203. Growth of the Bean Embryo. — As soon as the ground 

 is warm in the spring, farmers plant beans in rows. After 

 the bean seed has lain in the damp earth for about ten days, 

 the moisture has softened the seed coat and food, and the 

 shoots from the beans begin to show above the ground. 



The first part of the bean embryo to show is grown in the 

 little stem (hypocotyl). This curves sharply into an arch 

 and begins to push upward through the particles of soil. At 



the same time delicate 

 roots push downward 

 into the soil (Figure 

 258). As soon as the 

 arch of the hypocotyl 

 has pushed through the 

 soil into the light, it 

 straightens up and pulls 

 the seed leaves (coty- 

 ledons) out of the 

 ground. The seed coats 

 are usually left behind 

 in the soil. As soon as the cotyledons are exposed to the 

 light, they crack apart, slowly spread wide open, and in a 

 few days become green. During these changes in the coty- 

 ledons, the leaves of the plumule have taken from them 

 the food stored for the use of the growing bean embryo. 

 As soon as this store of food is absorbed by the young 

 bean plant, the cotyledons drop to the ground. The bean 

 seedling is no longer dependent on the food in the seed, 

 but is able to gain its food from the soil and air. 



During the summer the bean plant grows bean seeds, 

 and the farmers harvest the beans and store the seeds in 

 barrels, sacks, or wooden bins. The dry beans may be 

 kept for years and still grow bean plants at any time 

 when conditions are favorable. 



a 



Figure 258. — Germination of Bean. 



