24 PLAKT LIFE OK THE FAEK. 



tatoes, stri'ctly speaking, roots. Our best and truest con- 

 ception of a root as an organ of absorption is that of a 

 single fibril or of a dense mass of the finest fibrils root- 

 branches no thicker than a hair. These fibrils grow in 

 length close to their tips, the actual tip being covered 

 with a thin extinguisher-like cap of dead tissue the root- 

 cap already mentioned, and which serves as a shield to 

 the softer tissues within. The structure is of the sim- 

 plest, merely layers of cells such as before described, 

 arranged in more or less longitudinal ranks, the cells 

 themselves delicate and thin- walled. The fineness of the 

 root-fibril, its growth near the tip, its wonderful power 

 of motion, are all well adapted to permit of the fibril 

 ma*king its way between the particles of soil, and extract- 

 ing nourishment from the fluid surrounding them. We 

 have only to examine the root of a wheat plant, or still 

 better of a perennial pasture grass, to see how perfectly 

 this is accomplished. Under such circumstances the 

 root-fibrils form a dense wig, as it were, of feeding 

 threads which occupy the soil so thoroughly that the soil 

 is held together by them. It is easy to see that although 

 the absorbent power of each thread is infinitesimal, yet 

 in the aggregate it must be very large. Fine as they 

 often are, these root-fibrils are very frequently, but not 

 always, provided 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. 



Root Action What the Roots 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 



