AGEONOMY 



Taproots. In a large number of species the main root 

 continues to grow, becoming the main axis of the plant 

 underground. Such a root is called a taproot. Frequently 



the taproot is used for the storage 

 of food and is often much enlarged 

 for this purpose. Good examples of 

 taproots may be seen in the carrot, 

 parsnip, and dandelion. All our root 

 crops are cultivated for the food 

 stored by the plant in the main or 

 lateral roots. In some plants the 

 first root fails to keep ahead of the 

 others, and no taproot is found in 

 mature specimens. The root system 

 of the corn illustrates this. The 

 onion, hyacinth, and other lilylike 

 plants exhibit good examples of 

 what are called multiple primary 

 roots, where several roots of equal 

 size arise together from the base of 

 the stem. Plants with taproots are 

 said to have an axial root system ; 

 without a taproot it is inaxial. 

 Structure of the root. The young roots of plants are alike 

 in all essential particulars. In the center is a somewhat fibrous 

 portion known as the central cylinder, and surrounding it is a 

 softer layer, the cortex. On the outside is a thin skin formed 

 of waterproof cells, which is known as the epidermis. The 

 central cylinder has a series of small tubes, or ducts, running 

 lengthwise through it, and it is along these ducts that the 

 water absorbed by the plant travels upward. Roots that 

 continue to live for some years, annually spreading into 

 wider territory and absorbing a greater amount of food mate- 

 rial, need a larger number of ducts for transporting these 



FIG. 33. Taproot 

 parsnip 



The sectional specimen shows 

 the central cylinder and cortex 



