64 



PRACTICAL COURSE IN BOTANY 



inent. 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- 

 tice in the central cylinder 

 (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 



Fig. 80. — Cross section of a young root, 

 magnified : h, hairs ; a, cortex ; 6, central 

 cylinder ; e, sheath or endodermis ; ep, epi- 

 dermis; sp, cut ends of the duets. 



