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 
trlphyllum) . 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. 
