72 



Principles of Plant Culture. 



the food materials it contains. The root-hairs greatly 

 increase the absorbing surface of the roots, just as 

 leaves increase the absorbing surface of the 

 plant above ground. Each root-hair con- 

 sists of a single elongated cell (Mg. 30), 

 and is filled with protoplasm, as are the 

 cells in other living parts of the plant (13) . 

 As the extremity of the root advances 

 through the soil by growth, new root-hairs 

 are formed in front of the older ones, while 

 those farthest back as rapidly die off, so 

 that only a short portion of a rootlet bears 

 root-hairs at any one time. In Fig. 27 

 root-hairs are visible in the left glass, and 

 in Fig. 6 they may be seen on the hypo- 



JFiG. 2!J. Seed- „ „ , . ,. 



lings of turnip cotyl of somc of the germinating corn 



showing root- . . 



hairs. (After ffraius. In Fig. 29 A and m Fig. 28 the 



Frank and " ° . . 



Tschircb.) parts of the root bearing root-hairs are in- 



dicated by the sand which adheres to these parts. It is 

 usually difficult to see the root-hairs of plants growing 

 in the natural soil, but they may sometimes be dis- 



FiG. 30. Magnified root-hair of wheat, in contact with soli particles. 

 (After Sachs.) 



covered with the help of a pocket magnifying glass by 

 carefully removing the soil particles about the younger- 

 roots, when the silky network of root-hairs may be seen 

 filling the smaller pores of the soil or enveloping the 



