216 
their other constituent parts. And the leaves of 
the plants that grow in darkness or in shady places 
are uniformly pale ; their juices are watery and 
saccharine, and they do not afford oils or resinous 
substances. I shall detail an experiment on this 
subject. 
1 took an equal weight, 400 grains, of the leaves 
of two plants of endive, one bright green, which 
had grown fully exposed to light, and the other 
almost white, which had been secluded from light 
by being covered with a box ; after being both 
acted upon for some time by boiling water, in the 
state of pulp, the undissolved matter was dried, 
and exposed to the action of warm alcohol. The 
matter from the green leaves gave it a tinge of 
olive : that from the pale leaves did not alter its 
colour. Scarcely any solid matter was produced 
by evaporation of the alcohol that had been digest- 
ed on the pale leaves : whereas by the evaporation 
of that from the green leaves a considerable resi- 
duum was obtained ; five grains of which were 
separated from the vessel in which the evaporation 
was carried on ; they burnt with flame, and ap- 
peared partly matter analogous to resin. 53 grains 
of woody fibre were obtained from the green leaves, 
and only 31 from the pale leaves. 
It has been mentioned in the Third Lecture, 
that the sap probably, in common cases, descends 
from the leaves into the bark ; the bark is usually 
so loose in its texture, that the atmosphere may 
possibly act upon it in the cortical layers ; but the 
changes taking place in the leaves appear sufficient 
to explain the difference between the products 
