XXXII. THE RED MAPLE. 485 
autumn to one or a few leaves. The frost has very little to do 
with the autumncolors. Some trees are not perceptibly affected 
by it. The sober browns and dark reds, those of the elms and 
several of the oaks, may be the gradual effects of continued cold. 
The brighter colors seem to depend upon other causes. An 
unusually moist summer, which keeps the cuticle of the forest 
leaves thin, delicate, and translucent, is followed by an autumn 
of resplendent colors. A dry summer, by rendering the cuticle 
hard and thick, makes it opaque, and although the same bright 
colors may be formed within the substance of the leaf, they are 
not exhibited to theeye; the fall woods are tame; and the ex- 
pectation of the rich variety of gaudy colors is disappointed. 
The question why our forests are so much more brilliant, in 
their autumnal livery, than those of corresponding climates and 
natural families in Europe, cannot, perhaps, be fully answered. 
It depends, there can be little doubt, on the greater transparency 
of our atmosphere, and the consequently greater intensity of the 
light; on the same cause which renders a much larger number 
of stars visible by night, and which clothes our flowering plants 
with more numerous flowers, and those of deeper and richer 
tints; giving somewhat of tropical splendor to our really colder 
parallels of latitude. 
On the first evolution of the leaves in spring, and afterwards 
when they expand during a series of cloudy days, their color is 
a delicate yellowish-green, which is supposed to be owing to 
the green coloring matter within the cells of the leaves, the 
chromule, or chlorophylle, seen through their white or yellowish 
membranous coverings. A few hours of sunshine give a visibly 
deeper tint to the green, which becomes still more intense in the 
clear and bright sunshine of June and July. ‘This formation 
of green is found to be connected with the decomposition of the 
carbonic acid gas which is taken up in the sap, and the conse- 
quent evolution of oxygen, and the deposition of carbon in the 
vessels of the plant. The color of the chromule is therefore 
thought to depend upon its greater or less oxygenation ;—a free 
acid, that is, an excess of oxygenation, being sometimes found 
in the chromule, when it has become yellow or red. Minute 
portions of iron, carried up by the sap, and deposited in the 
