CHLOROPHYLE. (Endoehrome, Phytoehlore, Chromate.) The green colouring-matter of plants. It is obtained by bruising, press ing, and then washing leaves with water, and afterwards treating them with alcohol, which dissolves the green colour and wax ; when water is added to this solution, and the alcohol distilled, the green substance, which contains wax, floats on the surface of the water ; when this is heated with ether, the wax is dissolved, and Chlorophyle remains nearly pure. When exposed to light, or the action of chlorine, it is bleached. Acids produce a similar effect, and by the alkalis it is con verted into soap. The red tint which leaves assume in autumn appears to be owing to the formation and action of an acid ; the green colour is restored by an alkali.
This substance has been recently investigated with great care by Mulder, and the following account of it is chiefly derived from his researches as given in his Chemistry of Animal and Vegetable Physiology.' :— It is a striking fact that young leaves have a much lighter green colour than those which are older, showing that the quantity of Chlorophyle increases with the age of the leaves. If Chlorophyle were a substance poor in oxygen, and were derived from substances rich in oxygen, this fact alone would be sufficient to explain the power which the green parts possess of separating oxygen. This however is not the case : Chlorophyle is rich in oxygen. Nevertheless the leaves give off oxygen not because they are green, but whilst they are becoming green.
When green leaves are digested with ether the liquid becomes green. On evaporating the etherial solution, and treating the residue with hot alcohol, a considerable amount of white fatty matter (wax) separates on cooling, while the green colouring-matter remains in solution. Before proceeding to the consideration of the green colouring-matter, it will be expedient to say a few words respecting the mixture it forms with the wax.
In a physiological or botanical sense this mixture has the name of Chlorophyle ; in a chemical sense the term is restricted to the actual green pigment. To prevent confusion, the former is designated as B. Chlorophyle, and the latter as C. Chlorophyle ; B. indicating the botanical, and C. the chemical signification of word.
We find similar mixtures of a waxy fat and colouring-matter in other external parts besides the leaves, namely, In the skins of fruits, especially of such as are coloured ; and ou digesting them in ether we obtain a large quantity of waxy matter in solution, varying in tint according to the colour of the skin ; being gray when obtained from apples, and of a beautiful orange-colour when obtained from the berries of the Mountain-Ash.
The degree in which the action of light contributes to the change of colour in the C. Chlorophyle which exists in the perisperms, and to the production from it of the colouring-matter of the skin of ripe fruits, may be obviously inferred from the green colour which such fruits retain if they do not receive a sufficient supply of solar light, or froth the difference of colour exhibited by the opposite side of the same fruit, as well as from the fact that leaves when deprived of the action of light become colourless, while if completely exposed to its action they secrete a considerable amount of B. Chlorophyle.
This apparently anomalous difference in the action of light ou the skins of fruits and on leaves is dependent on the same cause as the change of colour in the leaves during autumn ; namely, that light can only produce B. Chlorophyle when there is a sufficient supply of materials for its renewed formation as often as the existing quantity is decomposed by the influence of the light ; and that as soon as this supply is exhausted the green colouring-matter is itself decomposed, and other compounds are formed from it.
Light acts powerfully in keeping plants green, and likewise exerts a powerful decomposing action upon all colouring-matters, the C. Chlorophyle not excepted ; thus asparagus, potatoes, young leaves, &c., become green whenever they are exposed to light, and hence there must be a substance widely diffused through plants, which causes the production of Chlorophyle. The change takes place not Merely on the surface, but beneath it as far as light can penetrate through the semi-transparent parts. All plants however are not coloured green ; some have no colour at all, while others are speckled or 'potted, or of a colour entirely different from green. Hence we conclude that in these plants or parts of plants, the materials yielding Chlorophyl° are absent. We may sometimes observe in summer one single spot of a green leaf coloured red by the action of insects or by being injured by hail ; the green colouring-matter is at the spot decom posed by the light ; no new portion is formed, and the spot acquires the same colour which the whole leaf would have assumed in autumn.