THE ROOT 



69 



a b 



FIG. 83. Dandelion : a, common form, grown in plains 

 region at low altitude ; b, alpine form. 



69. Root pull. Roots are not mere passive holdfasts, 

 but exert an active downward pull upon the stem. Notice 

 the rooting end 

 of a strawberry or 

 raspberry shoot 

 and observe how 

 the stem appears 

 to be drawn into 

 the ground at the 

 rooting point. 

 In the leaf ro- 

 settes of herbs 

 growing flat on 

 the ground or in 

 the crevices of walls and pavements, the strong depression 

 observable at the center is due to root pull. (Fig. 84.) 



70. Storage of food. Another of- 

 fice of roots is to store up food for the 

 use of the plant. This is done chiefly 

 in the tissues of fleshy roots and tu- 

 bers, and gives to them their great 

 economic value. Next to grains and 

 cereals, roots probably furnish a larger 

 portion of food to the human race 

 than any other crop. In addition to 

 this they are also the source of valu- 

 able drugs, condiments, and dyes. 



71. Absorption and conveyance of 

 sap. But the most important func- 

 tion of roots is that of absorption. 

 By their action the soil water and the 

 minerals contained in it are drawn up 

 into the plant body and made avail- 

 able f or conversion by the leaves into 



organic foods, as will be explained in another chapter. From 

 the nature of their function, most roots have naturally a 



FIG. 84. Raspberry sto- 

 lon showing root pull. 



