XXXIII. THE RED MAPLE. 485 



autumn to one or a few leaves. The frost has very little to do 

 with the autumn colors. 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 the eye ; 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 chlorojjhylle, 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 



