1 85 
of plants are found in their fluids, with the ex- 
ception of woody fibre. Fixed and volatile oils, 
containing resin or camphor, or analogous sub- 
stances in solution, exist in the cylindrical tubes 
belonging to a number of plants. Different 
species of Euphorbia emit a milky juice, which 
when exposed to air deposits a substance analogous 
to starch, and another similar to gluten. 
Opium, gum elastic, gamboge, the poisons of 
the Upas Antiar and Tieute , and other substances 
that exude from plants, may be considered as pe- 
culiar juices belonging to appropriate vessels. 
The sap of plants, in general, is very compound 
in its nature ; and contains most saccharine, mu- 
cilaginous, and albuminous matter in the al- 
burnum ; and most tannin and extract in the bark. 
The cambium, which is the mucilaginous fluid 
found in trees, between the wood and the bark, 
and which is essential to the formation of new 
parts, seems to be derived from these two kinds 
of sap ; and probably is a combination of the mu- 
cilaginous and albuminous matter of one, with 
the astringent matter of the other, in a state fitted 
to become organized by the separation of its 
watery parts. 
The alburnous saps of some trees have been 
chemically examined by Vauquelin. He found 
in those of the elm, beech, yoke elm, hornbeam, 
and birch, extractive and mucilaginous matter, and 
acetic acid combined with potassa or lime. The 
solid matter afforded by their evaporation yielded 
an ammoniacal smell, probably owing to albumen : 
the sap of the birch afforded saccharine matter, 
k 4 
