Cortex 



Epidermal 

 cells 



Central 



cylinder 



Root 

 hairs 



Root cap 



Radish seedling 



Hugh Spencer 



THE TIP OF A YOUNG ROOT 



Each root hair is a single cell formed by the outward prolongation of one of the skin 

 cells. Each root hair lives but a short time and then shrivels up. New root hairs are 

 formed as the tip of the root continues to grow. The older skin cells of the root die 

 and dry out, making a protective cover through which little water passes 



root. The tubes through which water passes from the roots to the leaves 

 are called xylem, or wood vessels; those through which organic foods pass 

 downward from the leaves to all other parts of the plant are called phloem, 

 or bast vessels. 



Associated closely with the two kinds of ducts, or tube-cells, there are 

 other elongated cells having rather thick walls of cellulose. These are the 

 fibers, which are usually more tough and rigid than those we find in the 

 carrot. The bundles of fibers and vessels together make up the "fibro- 

 vascular bundles", which are conspicuous in all our common plants above 

 the rank of mosses and liverworts — that is, from the ferns onward (see 

 Appendix A). 



The fibrovascular bundles of the root are continuous with those of die 

 leaf, by way of the stem. They branch and subdivide as the plant grows; 

 and in the leaves we can see the bundles reaching to all parts as "veins" 

 (see illustration opposite). 



The fibers are most conspicuous in the stems of plants, which we readily 

 recognize as mechanical supports. The wood of trees consists very largely 

 of fibers, as do the tough parts of bark. We make extensive use not only of 

 wood, but of the fibrovascular bundles of many plants in the form of 



144 



