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Page:Popular Science Monthly Volume 61.djvu/159

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esting details about seeds, leaf structure, etc. It is quite possible that the microscope may yet serve to answer the present disputed question as to how the water can rise into the tops of the great trees of California, some of which are over 300 feet from the ground. It may also be mentioned PSM V61 D159 Snow crystals photographed.pngFig. 19. Snow Crystals. that photomicrographs are of much importance in studying insects and parasites that infest and destroy forest and fruit trees. In fact, the preservation or annihilation, as seems best to serve man's purpose, of certain organisms is determined very largely by the revelations of the microscope. When such a thing as the lack of assimilating power of a leaf due to insufficient amount of light may be shown by a photograph, the far-reaching value of this science can be understood.

Its intimate connection with botany and plant structure in general is in fact so well recognized as to need little comment here. Some work in connection with cotton fibers, however, is interesting as it shows how it is possible to detect injury to the fiber in the process of ginning; such photographs in connection with others of like character, render valuable information concerning textile materials (Fig. 12).

In crystallography the photomicrograph is useful. Figs. 13-18 illustrate the appearance in polarized light of a few crystals of both organic and inorganic substances. Perhaps one of the richest of all substances in variety of form of crystals is snow. While the geometrical form is invariably hexagonal, it occurs in countless combinations and many of the crystals are very beautiful. For procuring pictures of snow crystals it seems necessary to use the apparatus in a temperature below the freezing point. The snow crystals are collected as they fall upon a surface too cold to tend to melt them, and if the work is done quickly,