182 A TEXTBOOK OF GENERAL BOTANY 
Growth of root hairs. Root hairs tend to grow out at right 
angles from the surface of the roots, but when they are in the 
soil they soon meet with soil particles and are thus turned aside. 
In doing this their surfaces conform to those of 
the particles around which they grow, so that they 
are in very intimate contact with the soil particles. 
Growth in root hairs occurs only at the tip, which 
is protected by having a thickened wall (Fig. 184). 
Growth at any point other than the tip would loosen 
the attachment of the hairs to the soil particles. 
Location of root hairs. Root hairs do not occur 

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Fia.185. Seed- 
ling of radish, 
showing root 
hairs grown in 
moistair. (x14) 
at the tip of the root or in the 
region of elongation. If they did 
occur in these places, they would, 
on account of their close contact 
with the soil particles, be likely to 
be broken as the tip was pushed 
through the soil. Root hairs are 
ephemeral structures, and after 
they have functioned for a short 
time they dry up and disappear, 
so that they occur in only a 
short zone, which is called the root-hair zone. 
Anchorage by root hairs. The close contact 
of the root hairs with the soil particles is of 
advantage in more ways than simply for absorb- 
ing water and minerals from the soil. The 
contact with the soil particles is so close that 
when the root is pulled from the soil either 
the hairs are broken off or the soil particles 
adhere to the roots (Figs. 185, 186). This adhe- 
sion of the hairs to the soil particles aids in anchoring the plant 
in the ground. It is also of advantage in that the part of the 
root which bears the root hairs is firmly anchored, so that when 
the more apical portion increases in length the root-hair zone is 
held firmly in position and the tip is shoved forward. 

Fic.186. Seedling 
of radish from seed 
planted in the soil 
Note the adherence 
of soil to root hairs 
and compare with 
Fig. 185. (x 14) 
