GROWTH AND WORK OF PLANTS 



This portion of the stem (hypocotyl) becomes quite long in 

 the bean, but is quite short in the corn. The cotyledons 



Fig. 7. 



Bean seeds germinating, seed coat slipping off. Beans germinating, one cotyledon removed, 



showing expanding plumule. 



are thus lifted above the ground. They become more or less 

 shrivelled and shrunken because of the food substance withdrawn 



for the growth of the seed- 

 ling, and finally fall away, as 

 the young membranous leaves 

 expand and the stem elon- 

 gates (fig. 9). 



In the scarlet runner bean, 

 and in the pea, the hypo- 

 cotyl remains short so that 

 the cotyledons are left in the 

 ground. The portion of the 

 Flg< 9> stem above the cotyledons 



How the garden bean comes out of the ground. 



First the looped hypocotyl then the cotyledons elongates and forms the loop 

 pulled out, next casting off the seed coat, last the 



plant erect, bearing thick cotyledons, the ex- as the Seedling emerges f rom 

 pandmg leaves, and the plumule between them. 



the soil so that the tender 



leaves and plumule are not injured, as they would be if pushed 

 up while they are standing erect. 



