ROOT CAP 



49 



whole may suffer injury; and the cambium lies beneath the bark 

 which gives it ample protection. But the tip of the root, as 

 it grows, must push its way through the harsh soil and is there- 

 fore provided with a special protective structure, the root cap. 

 This is a conical mass of cells 

 fitting over the tip of the root. 

 As the rootlet pushes forward 

 through the soil some of the cells 

 of the root cap are rubbed off 

 or destroyed, while others from 

 beneath take their places, new 

 ones being continually formed 

 for this purpose at the point of 

 growth in the base of the cap. 



Modified Roots 



103. In many plants, espe- 

 cially among biennials and per- 

 ennials, the roots show peculiar- 

 ities of form and structure which 

 cannot be accounted for with 

 reference to the usual functions 

 of roots, viz. , those of absorption 

 and anchorage. These modifi- 

 cations are often in the nature 

 of enlargements, as in the case 



Fig. 23. — Longitudinal section of 

 the tip of a rootlet with the root cap. 

 The lower third of the figure is the 

 cap. The region of growth (nnilli- 

 phcation of cells) is indicated by the 

 small size of the cells. The black 

 dots are the nuclei. 



In the spring of the second 



of the turnip and sweet potato, 

 year such roots give rise to new shoots from undeveloped or 

 adventitious buds. The root shrivels as the shoot grows 

 because of the gradual absorption of the contained food store, 

 the enlargement being due to the accumulation of starch or 

 other elaborated food substances. 



104. A less common type of root is the prop root, which 



4 



