Page:Popular Science Monthly Volume 6.djvu/76

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It will be at once observed that the absolute amount of nitrogenized substances differs widely as between the leaves of the two plants: there is at first far more in those of the maple than in those of the lilac, and this superiority is maintained during the whole period of vegetation.

Probably were we to examine from this point of view a large number of plants, we should find differences as great as these. Even between trees of the same species similar differences occur, according to their age and vigor, and more particularly according to the surroundings. Thus, on July 12, 1873, M. Corenwinder collected leaves of the common lilac in a garden situated in the open country near Saint-Quentin, and in them found:

Comparing this analysis with that of the lilac-leaves which were gathered at the same time, but in a city-garden, we see that those which had plenty of air, growing in the country, remote from aggregations of human beings, are the richer in nitrogenized substances. They also grow thicker and larger, the activity of respiration