begins at the summit, and, spreading over the surface, 
gradually reaches the stalk. The leaves of some 
plants pass from green to yellow, and afterwards 
become red ; those of other plants become red only 
when exposed to the sun, and assume a yellow co- 
lour in the shade ; while others pass from red 
to yellow, after they have fallen. It often hap- 
pens, that many leaves which usually redden, be- 
come dry without exhibiting this colour ; and appa- 
rently without regard to the immediate influence ei- 
ther of light or of heat. In all cases, red leaves lose 
their redness after a certain period, passing to yellow 
and white, and the direct action of the sun seems to 
accelerate these changes *. 
3 86. In this transition from a green to a red co- 
lour, the nerves and stalks of the leaves never red- 
den. As these parts were not previously green, it re- 
sults, says M. Senebier, that it is the green matter a- 
lone which suffers this change of colour ; and hence 
the stalks of the mdampyrum, which were previous- 
ly green, become red like the other parts of the leaf. 
In general, the superior surface of the leaf first 
changes colour, and often passes through various 
tints into yellow, before the inferior surface ceases to 
be green f. 
387. The leaves, which have thus become red by 
age, yield to water a yellowish red or brick colour, 
and a red one to alcohol. The green leaves of the 
Canadian vine impart their green colour to alcohol, 
but the red leaves of the same plant tinge it red. 
Mem. Phys. Chim. t. iii. p. 6$. 72, t Ibid. p. 73. 
