THE ROOT. 19 
extremity of the radicle, that is to say, at the points, but rather 
at a certain distance from the end, in the part marked in the 
engraving by the letter o. Be 
The material which these organs take up from the soil in order 
to pass them into its ae Mf JJ 
system must either be SS \ dpe 
gaseous or liquid. Solid : lage a DRO aa 
bodies however attenu- = <== i A : Hiei = 
ated, or however sub- = Ht id He i 1 = 
_ divided, even when held = tt | te: tt : 
in suspension in water, je it u i tt rH 
cannot penetrate into \ Ni et 
the infinitely narrow Wacoal Ha ' 
channels which the ex- RE ate by HH) 
tremities of the root- : Ne Nee Ea y) | 
fibres present. All NSS rary / 
eu so absorbed AWS ey) 
: pe NRE yy 
must therefore be in a WE Sy 
ee ee ea SS 
- solution in the water. 
The more important of 
these substances for the purposes of vegetation are the salts of 
potassium, of soda, of lime, ammoniacal compounds, and carbonic 
acid gas dissolved in water. 
But what is the mysterious power which produces the operation 
of absorption in plants, this operation by which a liquid from 
the exterior enters and traverses an organ already gorged with 
liquids? Botanists have now agreed that this result is due to 
the triple influence, to ‘the successive or combined action of 
endosmose of capillary attraction and a determinate attraction in 
the leaves. Let us explain ourselves. 
Take a small vessel, a, Fig. 21, formed of animal or vegetable 
membrane, containing sugared or gummed water, and plunge this 
vessel into another containing pure water. The liquid gum con- 
tained in the small vessel will be heavier than the pure water which 
surrounds it. This unequal density creates immediately a double 
current across the walls of the vessel ; the pure water flows towards 
the denser gum water, while the other flows in the opposite direc- 
c2 
Fig. 20,—Vertical section of the extremity of a root, seen 
in the microscope. 
