180 A TEXTBOOK OF GENERAL BOTANY 
In general the region of elongation is much longer in stems 
than in roots. This is probably connected, in part at least, with 
the fact that the air offers very little resistance to the growth of 
stems, while the roots, 
in growing through the 
SS = | soil, meet with con- 
: siderable resistance. If 
the elongating region 
of a root, which is com- 
posed of soft tissue, 
were of considerable 
length, the resistance 
offered to its move- 
ment through the soil 
would cause it to 











ae e 
th He a 






| 
7 a erumple. 
Fa if it a | i 
oe 
a ce - ABSORPTION OF 
a Ht es 
i 7 MATERIALS 




i 
Hi 
ee 
HH it HATH 
La 
Root hairs. We have | 
seen that one of the 
principal functions of 
ordinary roots is to ab-, 
sorb water. It is there- 
fore essential that they 
should have a large 
surface for the per- 
Fig. 183. Tip-of root of millet formance of this funec- 
Below is the rooteap. Above the capisthe region tion, as the larger the 
of elongation, and above this a portion of the root- absorbin 9 surface the 
hair zone showing growth of root hairs. (x 35) 
greater the rate of ab- 
sorption. Enlargement of the surface is produced by the growth 
of long, slender projections from the cells of the outermost 
layer, or epidermis, of the root. These projections are called root 
hairs (Fig. 183). Root hairs are not cut off from the epidermal 
cells but are simply projections from them (Fig. 184). Most of 




Ns 
Wi YD 
yy 
ey 
