ROOTS 43 
(c) The cortical portion, a tubular part enclosing the solid 
central cylinder. 
(d) The root-hairs, which cover some parts of the outer layer of 
the cortical portion very thickly. Observe particularly 
how far toward the tip of the root the root-hairs extend, 
and where the youngest ones are found. 
Make a drawing to illustrate all the points above suggested 
(a,b, c, d). Compare your drawing with Fig. 20. Make a careful 
study of longitudinal sections through the centers of the tips of very 
young roots of the hyacinth or the Chinese sacred lily. Sketch 
one section and compare the sketch with Fig. 20. 
Make a study of the roots of any of the common duckweeds, 
growing in nutrient solution in a jar of water under a bell-glass, and 
note the curious root-pockets which here take the place of root-caps. 
54. Details of Root-Structure.— The plan on which the 
young root is built has been outlined in Sect. 538. A few 
further particulars are necessary to an understanding of 
how the root does its work. On examining Fig. 21 the 
cylinders of which the root is made up are easily dis- 
tinguished, and the main constituent parts of each can be 
made out without much trouble. The epidermis-cells are 
seen to be somewhat brick-shaped, many of them provided 
with extensions into root-hairs. Inside the epidermis lie 
several layers of rather globular, thin-walled cells, and 
inside these a boundary layer between the cortical or bark 
portion of the root and the central cylinder. This latter 
region is especially marked by the presence of certain 
groups of cells, shown at w and d and at 6, the two 
former serving as channels for air and water, the latter 
(and w also) giving toughness to the root. 
Roots of shrubs and trees more than a year old will 
be found to have increased in thickness by the process 
