- 60 FOUNDATIONS OF BOTANY 
The growing tip of the root, as it pushes its way through 
the soil, is exposed to,bruises ; but these are largely warded 
off by the root-cap. The tip also shows a remarkable 
sensitiveness to contact with hard objects, so that when 
touched by one it swerves aside and thus finds its way 
downward by the easiest path. Roots with an unequal 
water supply on either side grow toward the moister soil. 
Roots are very tough, because they need to resist strong 
_ FIG. 28.— Roots of a Western Hemlock exposed by having most of the Leaf-Mould 
about them burned away by Forest Fires. 
pulls, but not as stiff as stems and branches of the same 
size, because they do not need to withstand sidewise pres- 
sure, acting from one side only. The corky layer which 
covers the outsides of roots is remarkable for its power 
of preventing evaporation. It must be of use in retaining 
in the root the moisture which otherwise might be lost 
on its way from the deeper rootlets (which are buried in 
damp soil), through the upper portions of the root-system, 
about which the soil is often very dry. 
