STORAGE OF RESERVE MATERIAL IN ROOTS 25 



of certain groups of cells, shown at w, d, and b (Fig. 21), the two 

 former serving as channels for air and water, the latter (and w 

 also) giving toughness to the root. 



Eoots of shrubs and trees more than a year old will be found to 

 have increased in thickness by the process described in Chapter 

 vii, and a section may look unlike that shown in Fig. 21. 



32. Storage of re- 

 serve material in 

 roots. Many roots 

 contain large quanti- 

 ties of stored plant 

 food, usually in the 

 shape of starch, sugar, 

 proteids, or all three 

 together. Parsnips, 

 carrots, turnips, and 

 sweet potatoes are 

 familiar examples of 

 storage roots. 



Beet roots contain 

 so much sugar that 

 a large part of the 

 sugar supply of 

 Europe, and an in- 

 creasing portion of 

 our own supply, is 

 obtained from them. Oftentimes the bulk of a fleshy root is 

 exceedingly large as compared with that of the parts of the 

 plant above ground. 



Not infrequently roots have a bitter or nauseous taste, as in 

 the case of the chicory, the dandelion, and the rhubarb ; and a 

 good many, like the monkshood, the yellow jasmine, and the 

 pinkroot, are poisonous. Evidently the plant may be benefited 

 by the disgusting taste or poisonous nature of its roots, which 

 renders them uneatable. 



FIG. 21. Much magnified cross section of a young 

 dicotyledonous root 



h, root hairs with adhering bits of sand; e, epi- 

 dermis; 5, thin-walled, nearly globular cells of 

 bark; b, hard bast; c, cambium; 10, wood cells; 

 d, ducts 



