220 



A YEAR IN SCIENCE 



Structure. In many plants the 

 root system contains one main root 

 much longer than any of its 

 branches. This is called a tap root. 

 Frequently food accumulates in 

 this main root forming a fleshy 

 tap root such as the carrot, radish, 

 dandelion, beet, or turnip. Some 

 plants have no single main root, 

 but many smaller roots arising 

 from the same point. These are 

 known as fibrous roots, examples 

 of which are found in all the 

 grasses. Sweet potatoes are thick- 

 .ened fibrous roots. The part of the 

 root near the stem may be large 

 and stout and covered with a thick 

 bark. The branches, however, 

 gradually become smaller, more 

 slender, and with a thinner cover- 

 ing, or epidermis. The ultimate 



branches give rise to many very delicate organs, the 

 root hairs. When a plant is pulled out of the ground, 

 the root hairs are generally broken off. Each of these 

 very numerous hairs is an extremely thin walled tube 

 which opens into the cell of the epidermis from which 

 it arises. 



Absorption of water and solutes. If we recall the 

 amount of water transpired by plants, we can form 



Fig:. 89. Seedling of 

 corn showing fibrous 

 roots. 



