CHAPTER XLI. 



THE ROOT 



I. Function of Roots. 



784. The most obvious function of tlie roots of ordinary plants 

 are two: jst, To furnish anchorage and partial support, and 

 2d, absorption of liquid nutriment from the soil. The environ- 

 mental relation of such roots, then, in Ijroad terms, is with the 

 soil. It is -^-erv clear that in some plants the root ser\-es both 

 functions, while in other plants the root may fulfil only one of 

 these requirements. 



The problems which the plant has to solve in working out 

 these relations are: 



(i) Permeation of the soil or substratum. 



(2) Grappling the sul)stratum. 



(3) A congenial moisture or water relation. 



(4) Distribution of roots for the purpose of reaching food- 

 laden soil. 



(5) Ivxposure of surface for absorption. 



(6) The renewal of the delicate structures for absorption. 



(7) Aid in ])reparation of food from raw material. 



(8) The maintenance of the required balance between the 

 environment as a whole and the increasing or changing require- 

 ments of tlie plant. 



785. (i) Permeation of the soil or substratum. — The funda- 

 mental di\'ergence of character \n the eii\-ironmental relations of 

 root and stem are manifest as soon as thev emerge from the 

 germinating seed, lender tlie influence of the same stimulus 

 (gravity) tlie root shows its geotropic tharatter ])y growing down- 



410 



