198 
PLANT STUDIES 
surface of the globular, cylindrical, or flattened stems (see 
36). 
140. Hairy coverings. A covering of hairs is an effective 
sun screen, and it is very common to find plants of xerophyte 
regions character- 
istically hairy (see 
35). The hairs 
are dead struc- 
tures, and within 
them there is air. 
This causes them 
to reflect the light, 
and hence to ap- 
pear white or 
nearly so. This 
reflection of light 
by the hairs dimin- 
ishes the amount 
which reaches the 
working region of 
the plant (see Fig. 
174). 
141. Body habit. 
Besides the va- 
rious devices for 
diminishing ex- 
posure or leaf sur- 
face, and hence 
loss of water, 
enumerated above, 
the whole habit of 
the plant may em- 
phasize the same purpose. In dry regions it is to be observed 
that dwarf growths prevail, so that the plant as a whole 
does not present such an exposure to the dry air as in 
regions of greater moisture (see Fig. 175). Also the pros- 
FIG. 115. Two plants of a common scouring rush (Equi- 
setum}, showing the effect of environment ; the long, 
unbranched one having grown in normal mesophyte 
conditions ; the short, bushy branching, more slender 
form having grown on the dunes (xerophyte condi- 
tions). After COWLES. 
