90 
PLANT STUDIES 
by numerous thread-like processes spreading in every direc- 
tion than by flat, expanded processes. 
It should also be noted that as soil roots are subterra- 
nean they are used often for the storage of food, as in the 
case of many subterranean stems. Certain prominent root 
types may be noted as follows : 
64. Soil roots. These roots push into the ground with 
great energy, 
i / \ u and their ab- 
r.i\D\if. t f 
sorbing sur- 
faces are en- 
tirely covered. 
Only the young- 
est parts of a 
root system 
absorb actively, 
the older parts 
transporting 
the absorbed 
material to the 
stem, and help- 
ing to grip the 
soil. The soil 
root is the most 
common root 
type, being 
used by the great majority of seed plants and fern plants, 
and among the moss plants the very simple root-like pro- 
cesses are mostly soil-related. To such roots the water of 
the soil presents itself either as free water that is, water 
that can be drained away or as films of water adhering to 
each soil particle, often called water of adhesion. To come 
in contact with this water, not only does the root system 
usually branch profusely in every direction, but the youngest 
branches develop abundant absorbing hairs, or root hairs 
(see Fig. 84), which crowd in among the soil particles and 
PIG. 84. Root tips of corn, showing root hairs, their position 
in reference to the growing tip, and the effect of the 
surrounding medium upon their development : 1, in soil ; 
2, in air ; 3, in water. 
