154 PHARMACEUTICAL BOTANY 
Osmosis AppLIED TO Root-Hatrs.—Normally the cell sap of 
the root-hairs is a denser liquid than the soil water outside of 
1 2 
Fic. 91.—Successive stages of plasmolysis. JV, nucleus; V, vacuole; p, proto- 
plasm; e, area formerly occupied by protoplast now replaced by plasmolyzing 
solution. (Palladin after de Vries.) 
the hairs. The outer plasma membrane and the vacuolar 
membranes represent porous osmotic membranes separating the 
denser solution within the hair 
from the less dense soil water 
without. The soil water 
imbibed by the cell wall passes 
by osmosis through the outer 
plasma membrane, _ diffuses 
through the cytoplasm to the 
vacuolar membranes through 
which it passes by osmosis into 
the sap vacuoles and_ there 
becomes a portion of the cell 
sap. ' 
_ The kind of osmosis just indi- 
cated is known as endosmosis or 
osmosis from without in. A 
Fic. 92.—Root-hairs, with soil-particles 
adheae: (Case, after Sachs) reverse process takes place 
when small traces of COs, acid 
and other substances are excreted, ¢.g., passed out of the root- 
hair. This is called exosmosis. 
