Page:Popular Science Monthly Volume 49.djvu/86

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74
THE POPULAR SCIENCE MONTHLY.

dissolved in minute oil drops suspended in special masses of protoplasm, as is the case with chlorophyll.

Although this article is particularly concerned with the non-green colors of plants, yet it will be necessary to outline the function and adaptations of chlorophyll, to which these substances

PSM V49 D086 Curves showing regions of the solar spectrum.jpg

Fig. 2.—Curves showing Brightness and Synthetic, Thermal and Disintegrating Effects of the Regions of the Solar Spectrum.

bear a special relation. Chlorophyll is perhaps the most important coloring substance in the world, for upon this substance depends the characteristic activity of plants, the synthesis of complex compounds from carbon dioxide and water—a process upon which the existence of all living things is ultimately conditioned. Only in a very few unimportant forms devoid of chlorophyll can the synthesis of complex from simple compounds or from the elements be accomplished. The function of chlorophyll may only be comprehended when its chief physical properties are understood. These may be best illustrated if a solution of the substance is obtained by placing a gramme of chopped leaves of grass or geranium in a few cubic centimetres of strong alcohol for an hour. Such a solution will be of a bright, clear green color, and when the vessel containing it is held in such a manner that the sunlight is reflected from the surface of the liquid it will appear blood-red, due to its property of fluorescence, that of changing the wave length of the rays of light of the violet end of the spectrum in such manner as to make them coincide with those of the red end. It is by examination of light which has passed through a solution of chlorophyll, however, that the greatest insight into its physical properties may be gained. If such a ray of such light is passed through a prism and spread out on a screen, it may be seen that there are several large intervals or dark bands in the spectrum. The rays of light which would have occupied these spaces have been absorbed by the chlorophyll, and