ROOTS 
91 
absorb moisture from them. By these root hairs the absorb- 
ing surface, and hence the amount of absorption, is greatly 
increased. Individual 
root hairs do not last 
very long, but new 
ones are constantly ap- 
pearing just behind the 
advancing root tips, 
and the old ones are 
as constantly disap- 
pearing. 
(1) Geotropism and 
hydrotropism. Many 
outside influences affect 
roots in the direction 
of their growth, and 
as soil roots are espe- 
cially favorable for ob- 
serving these influ- 
ences, two prominent 
ones may be mentioned. The influence of gravity, or the 
earth influence, is very strong in directing the soil root. 
FIG. 85. Apparatus to 8how the response 
to water (hydrotropism) upon the part of 
roots. The ends -(a) of the box have hooks 
for hanging, while the box proper is a cylinder 
or trough of wire netting and is filled with 
damp sawdust. In the sawdust are planted 
peas (y), whose roots (A, z, k, m) first, descend 
until they emerge from the damp sawdust, 
but soon turn back toward it. After SACHS. 
FIG. 86. 
A raspberry plant, whose stem has been bent down to the soil and has 
root." After BEAL. 
struck 
