CHAPTER VIII 



THE ROOT. — FUNCTION AND STRUCTURE 



The function of roots is twofold, — to provide support or 

 anchorage for the plant, and to collect and convey food ma- 

 terials. The first function is considered in Chapter VII; 

 we may now give attention in more detail to the second. 



The feeding surface of the roots 

 is near their ends. As the roots 

 become old and hard, they serve 

 only as channels through wJiicJi 

 food passes and as holdfasts or 

 supports for the plant. The root- 

 hold of a plant is very strong. 

 Slowly pull upwards on some plant, 

 and note how firmly it is anchored 

 in the soil. 



Roots have power to choose their 

 food; that is, they do not absorb 

 all substances with which they 

 come in contact. They do not take 

 up great quantities of useless or 

 harmful materials, even though 

 these materials may be abundant in the soil ; but they 

 may take up a greater quantity of some of the plant-foods 

 than the plant can use to advantage. Plants respond very 

 quickly to liberal feeding, — that is, to the application of 

 plant-food to the soil (Fig 40). The poorer the soil, the 

 more marked are the results, as a rule, of the application 



Fig. 40. — Wheat growing 

 under Different Soil 

 Treatments. Soil defi- 

 cient in nitrogen ; com- 

 mercial nitrogen applied 

 to pot 3 (on right). 



