ENDOSMOSE., 57 
to the water; so that, after a little time, the tube 
containing the milk is fuller than that containing 
the water, as is represented in the figure 2. This 
in-rushing tendency of a thin fluid when only 
separated from a thicker, such as milk, by a 
delicate membrane, is called Endosmose. It is 
supposed in the case of plants, that the greater 
thickness or viscidity of the sap acts like the milk 
in the tube, and attracts the thinner water from 
the earth surrounding the roots, into the roots 
themselves, and thus a sort of motion becomes 
established. Undoubtedly the first is the most 
powerful cause of the two. 
The sap of plants is often highly valuable to 
man. In North America an immense amount 
of sugar is obtained almost exclusively from the 
sap of the Maple: by boring a hole a proper 
distance into the trunk, and fitting a wooden 
tube to it, the free end of which dips into a 
suitable vessel, a large daily supply of sweet 
juice is obtained, which, on undergoing the boil- 
ing and purifying processes of the manufacture, 
yields a very pure and pleasant sugar. Several 
members of the royal Palm tribe also furnish a 
highly valuable sap. In the fair Island of Ceylon 
