Abstract
IT would be impossible for me not to look upon the appearance of such a work as the one recently published by Dr. Gregor Kraus with much satisfaction, since the chief object of the author is to call the attention of his countrymen to the value of the spectrum-microscope in studying the colouring-matters of plants. He commences with a description of the instrument, and says that, though originally designed for the examination of microscopical objects, it is not only as useful as any larger spectroscope for the study of the absorption of soutions, but indeed in many cases preferable. He describes two different kinds of eye-piece, viz., a simple form made by Merz, and the far more complete Sorby-Browning, with the method of measurement proposed by Mr. Browning, and expresses his regret that the value of such instruments has been almost altogether overlooked by German botanists. In treating on the application of the apparatus, the author very justly points out the great advantage of having a bright illumination, without too much dispersion, and the importance of being able to examine the spectrum of a leaf or any other object in its natural state, in order to ascertain whether the colouring matters dissolved out from a plant by any solvent do really occur in it, or are products of decomposition. I would also myself add that in some cases the difference between the spectrum of a substance in a free state and when dissolved is so considerable that care must be taken not to conclude that there has been actual decomposition, until the character of the spectrum of the solid substance, in a free state, has been ascertained; and even when the spectra are very nearly the same, the position of the absorption-bands may differ sufficiently to make it possible to determine whether a colouring-matter naturally exists in a free state or dissolved in water, or in an oil, according as it is or is not soluble in water. The fact of being thus dissolved or not is in some cases, probably, a question of considerable physiological importance, since the existence of solid particles along with, or even actually surrounded by, a liquid capable of dissolving them, points to a very different origin and relation to Structure to those of a substance merely dissolved in the juices of a plant or an animal. The solution of such a colouring-matter is sometimes one of the first changes that occur in decomposition, as if set free from minute cells.
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SORBY, H. Chlorophyll Colouring-Matters†. Nature 8, 202–204 (1873). https://doi.org/10.1038/008202d0
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DOI: https://doi.org/10.1038/008202d0