236 



THE SECOND BOOK OF BOTANY. 



the dead cells (a) at the extreme end form a sort of 

 root-cap, which protects the living point from injury 

 as it pushes its way through the earth. These dead 

 cells are gradually sloughed off, and replaced by the 

 addition of worn-out cells from within. As these 

 root-tips absorb moisture from the soil, they have 

 been called spongioles, though incorrectly. 



The surface of the growing parts of roots is often 

 densely covered with minute hairs. Fig. 405 repre- 

 sents a portion of barley -root 

 highly magnified, and you see 

 the hairs are tubular elongations 

 of the outer root-cells. They are 

 more abundant in poor than in 



FIG. 405. 



FIG. 406. 



good soils. They wither with 

 age, and are replaced by new ones 

 nearer the extremity of the young- 

 est branches and fibres. Pull up 

 a young radish, and observe its surface. Compare it 

 with A (Fig. 406). Rinse away the dirt, and com- 



