20 PLANT LIFE ON THE FARM. 



these root-fibrils are very frequently but not always pro- 

 vided with yet finer " root-hairs." These are extremely 

 minute threads emerging from the superficial cells of the 

 root, in the vicinity of, but not exactly at their tips. When 

 their growth is stimulated by the presence of moisture 

 or suitable plant food, they often occur in such numbers 

 as to form a dense cobweb-like investment to the roots. 



Boot Action What the Boots do. It has been proved 

 by repeated experiments that the absorption of liquid food 

 (no solid matter can in any case be absorbed) takes place 

 towards the lower end of the .root-fibrils and by means of 

 these root-hairs when they are present. The upper portions 

 of the fibril do not act as absorbent organs, the root-hairs 

 do not exist in this part of the root, the structure of which 

 becomes gradually less and less adapted for absorption, so 

 that the actual space in each fibril devoted to absorption is 

 relatively small in relation to its length. The remainder 

 of the fibril acts as a conduit for the transmission of the 

 absorbed fluids upward from cell to cell by osmosis and 

 imbibition, and as a holdfast. 



The passage of the insoluble matters in the soil into the 

 root is effected by an acid liquid produced by the root-bail- 

 or cell in consequence of its contact with the particle of 

 soil, aided by the water in the soil. This acid fluid satu- 

 rates the cell walls, corrodes and effects the solution of the 

 surface of tjie particle of the soil in contact with the fibril 

 or root-hair. No passage of acid fluid out of the cell takes 

 place, root excretions having no existence; but the cor- 

 rosive, and as it were digestive, action above mentioned, is 

 due solely to the absolute contact of the cell of the root 

 with the particle of the soil. 



