42 ESSENTIALS OF BOTANY 



water supply on either side grow toward the moister soil. 

 Roots are very tough, because they need to resist strong 

 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. 



55. Propagation by Means of Roots Some familiar 



plants, such as rose bushes, are usually grown from roots 

 or root-cuttings. 



Bury a sweet potato or a dahlia root in damp sand and watch 

 the development of sprouts from adventitious buds. One sweet 

 potato will produce several such crops of sprouts, and every sprout 

 may lie made to grow into a new plant. It is in this way that the 

 crop is started wherever the sweet potato is grown for the market. 



86. Review Summary of Roots. 



Kinds of roots as regards origin J 



Kinds as regards medium in which they grow . 



Structure of root of a tree. 



f materials. 

 Storage in roots <| location. 



I. uses. 



Absorption of water by roots [ apparatus. 



[ amount. 



■ nature. 

 Movements of roots <j causes. 



. uses. 



