The Root and the Soil. 69 
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. 25, root-hairs are visible in 
the left glass, and in Fig. 5, they may be seen 
on the hypocotyl of some of the germinating 
corn grains. In Fig. 27 A, and in Fig. 26, the 
parts of the root bearing root-hairs are indi- 
cated by the sand which adheres to these 
parts. It is usually difficult to see root-hairs 
of plants growing in the natural soil, but they 
may sometimes be discovered, with the help 
of a pocket magnifying glass, by carefully 
removing the soil particles about the younger 
fet Riad roots, when their silky network may be seen 
showing root- filling the smaller pores of the soil, or envelop- 
oe ing the soil particles. Fig. 28 shows a mag- 
Frank and 
Techirch). nified root-hair of the wheat plant, closely 
Fre. 23. Magnified root-hair of wheat, in contact with soil partic'es. (After 
Sachs). 
attached to some particles of soil. The root-hairs are able 
to take up water freely, even from soil that does not appear 
very wet, because each soil particle is enveloped in a thin 
layer of water (91). Still more interesting is the fact, that 
root-hairs are able to dissolve mineral matters in the soil, 
by means of excretions, most important of which is carbonic 
acid, thus permitting the plant to use these matters as food. 
