ABSORPTION OF WATER 



51 



47. Structure of Root -hairs.— 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-likfe sac, closed at both 



Fig. 37. — Jack-in-the-pulpit (Ariscstna 

 triphyllum) . Longitudinal section 

 through a root, rt, root- tip; re, root- 

 cap. (After F. L. Pickett.) 



Fig. 38. — Roots of the water- 

 hyacinth (Eichornia crassipes 

 Solms), showing removable 

 root-caps; b, 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. 



