dioxide,- readily pass through the epidermis, both from within and without, the passage of water even, either by endosmosis or exos-mosis, experiences greater difficulty, some reagents finding even a less ready entrance and when they have entered, some of them fail to produce any effect, because they do not exert any solvent action on the chlorophyll. I enter into these particulars to simplify matters; even alcohol penetrates the epidermis very slowly and sparingly in the case of an entire and unbroken leaf and extracts so little of the chlorophyll that after two or three days immersion, the solution becomes only of a pale green colour. In order to obtain the full solvent action of the alcohol, it is necessary to cut the leaf up into very small pieces and even then the alcohol or other reagent used, enters the leaf but slowly and only through the cut edges or broken surfaces of the leaves. Chlorophyll is soluble in alcohol, ether and benzine, but not, it is usually stated, in water; it is also affirmed that it is soluble in acids, but I find that neither of these statements is altogether correct; it is often slightly soluble in water, as will be shown later in, while most acids, especially the organic acids, have little or no visible solvent action; the alkalies on the contrary exert a marked effect. [text?] But there is still another circumstance to be referred to in explanation of the difficulty with which chlorophyll is reached by some reagents and that is the presence of a wax-like material which renders the chlorophyll more or less impermeable to water and some other substances.
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On the Colour of Leaves of Plants and their Autumnal Changes, 1892. From The Royal Society, AP/69/1
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