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Page:Popular Science Monthly Volume 49.djvu/821

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acterized. A peculiarity of opposite style is presented in the leaf of the tulip tree, which is unique in shape, being cut off at the PSM V49 D821 Red mulberry leaves.jpgFig. 6.—Red Mulberry. end and having a marked hollow or notch where nearly every other leaf is angular or convex.

Our space is filled, and we have said nothing of the pinnate leaves, or the spiny leaves, or the leaves of the spruces and firs, of all of which as interesting studies might be made.

The greatest sphere of usefulness which a tree occupies, Mr. Mathews says, is connected with its life. It is a great air purifier; it absorbs from the atmosphere the carbonic-acid gas which is poisonous to us; it holds and slowly dispenses moisture which the parched air needs; it gives out the ozone (or oxygen in an active electronegative condition) which is peculiarly conducive to our health; and it modifies heat which would otherwise be overpowering. Each leaf is a builder up and an air regulator of a nature which is beneficial to us. "Its capacity for heat and sunshine is something astonishing. I have estimated that a certain sugar maple of large proportions, which grows near my cottage, puts forth in one season about four hundred and

thirty-two thousand leaves; these leaves combined present a surface to sunlight of about twenty-one thousand six hundred square feet, or an area equal to pretty nearly half an acre. Every inch of this expanse breathes in life for the tree, and out health for man, while it absorbs in the aggregate an enormous amount of heat and sunlight. In time of rain it also holds the moisture, and allows it to evaporate by slow degrees when hot days return. The forests are vast sponges, which, through the agency of leaves, soak up the beneficent raindrops and compel them