64 PRACTICAL COURSE IN BOTANY 
ment. Its innermost row of cells is thickened into the 
sheath, or endodermis (e), which serves as an additional 
protection to the conducting tissues. The extreme outer 
layer, from the cells of which the root hairs are developed, 
is, as already stated, the epidermis, and in the older and 
more exposed parts of perennial roots is displaced by the 
bark, which becomes indistinguishable from that of the 
stem. (66.) 
(c) Look at the tip of the root for a loose structure (c) 
fitting over it like a thimble. ‘This is the rootcap. Do you 
see any loose cells that seem to have broken away from it? 
These are old cells that have been pushed to the front by 
the formation of new growth back of them, and, being of no 
further use, are rubbed off by friction as the root bores its 
way through the soil. Draw a longitudinal section of the 
root as it appears under the microscope, labeling all the parts. 
If they cannot be made out distinctly in the specimen exam- 
ined, use sections of young corn or bean roots, which are 
larger and show the parts more distinctly. 
(d) Place under the microscope a thin cross section 
through the hairy portion of a primary root of a bean or pea 
seedling, and try to make 
out the parts noted above 
and shown in cross section in 
Fig. 80. Make a sketch of 
what you see, labeling all 
the parts you can recognize. 
Show in your drawing the 
differences in the size and 
shape of the cells composing 
the different tissues. No- 
Fic. 80. — Cross section of a young root, 5 2 ; 
magnified: h, hairs; u, cortex; b, central tice in the central cylinder 
cylinder ; e, sheath or endodermis ; ep, epi- 
dermis; sp, cut ends of the ducts. 
(Fig. 80) several groups of 
what look in the section like 
little round pits, or holes, sp. These are the cut ends of 
large-sized tubes or ducts that convey the water absorbed 
