CHAPTER XII 



WATER AND MINERAL NUTRIENTS.— ROOT ACTION 



145. Plant-food. — Having learned what a plant is and 

 having seen it as a whole, we may now inquire how it secures 

 food with which to live. We can discuss only the outlines 

 of the subject here: the pupil may consider the question 

 again when he takes up Part III. The plant secures water 

 and mineral nutrients from the soil. It also takes up mineral 

 elements which are not nutrients, but which enter the plant 

 because they are in solution in the soil-water. The word 

 plant-food is used commonly to include the water and 

 mineral nutrients taken in by the roots. Technically, the 

 word plant-food is used to designate such products as 

 starch, sugar, fats and other substances elaborated by 

 the plant. The latter usage is unfortunate, but we shall 

 follow it here, according to botanical usage, to avoid 

 confusion. ,. a^ 



146. Root Structure. — Roots divide &LlJ80% 

 into the thinnest and finest fibrils: there fi 

 are roots and there are rootlets. The large, 

 fleshy root of the radish (Fig. 120) ter- 

 minates in a common-sized root to which 

 little rootlets are attached. There are 

 also little rootlets attached to the fleshy 

 root at various places near the base. But 

 the rootlets that we see are only inter- 

 mediary, and there are numerous yet 

 smaller structures. 



147. The rootlets, or fine divisions, are clothed with 

 root-hairs (29), which are very delicate structures. Carefully 



(69) 



120. Root ami rootlets. 



