ROOTS: KINDS OF ROOTS 



35 



tions of roots which have become large and fleshy, as in the 

 sweet potato or the dahlia. Such roots are reservoirs where 

 plant food is stored to be used later by the plant for growth or 

 seed production or for starting new plants. In the sweet potato 

 the food is stored as sugar, while in the dahlia it is stored as 

 inulin, common in many composites. In the natural condition 

 inulin is in solution, but by prolonged immersion of the tissue in 

 alcohol the inulin is precipitated in the form of sphaero crystals. 

 Sweet potatoes are propagated by planting the potato to obtain 

 the young shoots, large numbers of which spring from adventi- 

 tious buds (paragraph 88). 



59. External structure near and including the root tip. 

 The principal general features in the structure of roots can be 

 obtained in the study of the roots of seedlings. The form of the 

 extreme tip is conic, and it consists of a group of cells which are 

 loosely held together, especially on the outer surface, where they 

 constantly become free and die. 

 This loose group of cells is the root 

 cap, and it protects the delicate 

 growing cells just back of the tip. 

 A splendid example of the root cap 

 is afforded by the screw pine. It is 

 very large and can very readily be 

 seen on the prop roots before they 

 reach the soil. Another interest- 

 ing example is found on the roots 

 of the water hyacinth common in 

 some of the streams of Florida and 

 sometimes grown in aquaria in 



greenhouses. The root cap is long Germ inating whea" showing root hairs. 

 and can be very easily pulled from 



the root and then slipped on again. Just back of the root cap 

 and still near the tip, the surface of the root is smooth and the 

 cells are united closely and firmly. The outer layer of cells, 

 somewhat elongated and rectangular, forms the "skin" or epi- 

 dermis as it is more properly called. A little farther back from 



Fig. 38. 



