38 



TUE EVOT 



water, except for a short disUuice from tlie ti|i ljaek«'ard. 

 Onli/ the parts inost recentlii formed are aetlee i)i absorption. 



53. The production of n3w rootlets is tlms of high iinpovtance. 

 Accordingly, as Jong as the i_Jaiit giows above grouuch auJ expands 

 fresh foliage from which moisture largely escapes into the air. so long 

 it continues to extend and multiply its roots in the soil beneath, re- 

 newing and increasing the fresh surface for alisorbing moisture in 

 proportion to the demand from above; and when growth ceases above 

 ground, and the leaves <lie aiul fall or no longer act, then the roots 

 generallv stop growing, and their soft and tender tips harden. From 

 this period, therefore, until growth begins anew the next spring, is the 

 best time for transplanting, especially for trees and shrubs. 



54. The action of root hairs. — It has alread}' been 

 noted in the hxlxiratory that the tip of the seedling root is 

 for a space smooth, hut that at a little distance back a 

 thick coA'ering of root Irairs soon arises. These not only 

 insinuate theniseh'es into the interspaces of the soil along- 

 side of the root, and stick up \\"hatever "water may be 



there ; but they appl}' 

 tliemselves closely to the 

 soil particles, the "walls 

 even becoming lobed and 

 distorted in order to gain 

 closer contact witli the 

 uneven parti{;'les compijs- 

 ing the soil (Fig. 21). 

 For adhering to the sur- 

 faces of the latter arc certain substances mrich needed by 

 the plant. These substances, mineral salts, ^ are not re- 

 mo\"ed by the simple flow of soil \\"ater," ijut remain firmly 

 Ijoiuid until acted upon by the root hairs. At the points of 

 contact, tlie root hairs excrete an acid ^^■]lich acts to release 



1 Salts such as potassium nitrate (saltpeter), magnesium sulphate, 

 calcium phosphate, etc. 



2 Fertilizers applied to land and dissolved by the rain are held in the 

 same manner by the soil, until taken by the roots of the crops. But if 

 applied when the ground is frozen, the fertilizers do n"t penetrate tlie 

 absorbent soil to the same extent, and much is washed away by surface 

 drainage, and lost. 



27. A rout liair, luucli niagnilicd. It is 

 seen to be a tultular (mtgro^\Uli 

 from an exterii.ir cell of the root, 

 in this case rnucli distorted. 



