ABSORPTION OF WATER 



47. Structure of Root -hair s.-The structure of root- 

 hairs, and their relation to the root as a whole, are illus- 

 trated in Figs. 40 and 41. It is seen at once that they 

 are epidermal cells, elongated at right angles to the sur- 

 face of the root, forming a thread-like sac, closed at both 



FIG. 37. Jack-in-the-pulpit (Ariscema 

 triphyllum). Longitudinal section 



FIG. 38. Roots of the water- 

 hyacinth (Eichornia crassipes 



through a root, rt, root- tip; re, root- Solms), showing removable 



cap. (After F. L. Pickett.) 



root-caps; 6, root-cap removed 

 from c. 



ends. The typical cell-structure is readily recognized 

 cytoplasm, nucleus, vacuoles, sometimes merged into one 

 large vacuole, cell-sap, and finally the cell-wall. It has 

 recently been shown that the cell-wall is composed of an 

 inner layer of cellulose and an outer layer of calcium 

 pectate. 



