ROOT SYSTEM 



2(37 



206. The Bean Seedling — Each bean seedling is provided 



with a supply of food which gives it a start in life. But 

 after this supply is exhausted, the young beao must be 

 able to prepare its own food. The Beveral parts of the 

 bean seedling are the roots, stem, and leaves, all of which 

 work in preparing the seedling's food. 



207. Root System. — The first root to form on the bean 

 is called the tap or primary root and grows straight 

 downward. Many 

 branches, known as 

 secondary roots, grow 

 from the taproot. 

 These large secondary 

 roots serve chiefly to 

 hold the plant firmly 

 in place. From the 

 secondary roots smaller 

 branches or rootlets 

 grow, and on these, a 

 short distance back 

 from the tip, are nu- 

 merous root hairs. 



In order to under- 

 stand the other great 

 use of roots, we must 

 be familiar with their 

 structure. A cross sec- 



Figure 259. — Bean Plants. 



All the food these plants have used came 

 from the cotyledons, as the jar contained 

 only sawdust. 



tion of a taproot shows three regions. In the central part 

 is a woody portion called the central cylinder. Next i«> and 

 outside of this is a layer known as the endoderm (Greek, 

 endo, within ; derm, skin) which separates tin- central 

 cylinder from the next region, the cortex (hat in, cortex, 

 bark). Outside of all is a thin protective layer, the 

 epidermis. 



