24 PLANT LIFE ON THE FARM. 
tatoes, strictly speaking, roots. Our best and truest cor- 
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 
making 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 bythem. 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, providel 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 
