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 

 ofE 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. — Koots 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. 



