14 ELEMENTS OF BOTANY. 
* 
are surrounded by the moist soil and wrap themselves around 
microscopical particles of earth. Thus they are able rapidly 
to absorb through their thin walls the soil-water, with what- 
ever mineral substances it has dissolved in it. 
18. The Root-Cap.—The tips of young roots and rootlets, 
Fic. 4.—Apparatus for Measurement of Growth. 
as they bore their way through the soil, are protected from 
injury by a coating of loose cells, called the root-cap, shown 
at d in Fig. 3. It will be seen from this figure that no root- 
hairs proceed from the root-cap, and indeed there is very 
little absorption of water going on in this place. In the so- 
