Vegetable Photography.

Oamaru Mail, Volume XXXV, Issue 10016, 5 December 1908, Page 3 (Supplement)

Vegetable Photography.

The interesting discovery -that leaves and other -vegetable substances when placed in contact with a plate m darkness will give rise to a photographic image has already bean noted in these •columns. Exhaustive experiments by Dv Russell; described in Cosmos by tiaul' Combes, seem to show that this action is not .due to radioactivity, as was naturally supposed at first, but to direct chemical action of some sort, possibly that of hydrogen peroxid. Says jVL Comfces: "It is the same with all vegetable forms—stems, leaves, flowers, seeds, tubercles, bulbs, etc. This has been demonstrated in a series of experiments mada by Mr Russell on all kh....... of vegetation, from the germinating seeo, up to tlie c'onipletelly developed form, and even on the dried plant alter its death. Certain of the most important vegetable substances, however - , .axe exceptions to the rule, notably starch, cellulose; gum, sugar; pith, and pollen. Any kind of rapid photographic plate whatever may be used in these experiments, and the development is earned oil in the ordinary way with the usual materials. That vegetable substances may act on the sensitive layer and give' the best results, it is necessary that they should be properly dried ; otherwise the moisture that they contain might alter'the gelatine layer and destroy, the image. The diiration of contact may vary irorn a. few'minutes to eighteen hours or more. The action may be hastened by heating, but the temperature should not exceed s£deg. C. (loldeg. F.); on the other hand, the contact under ordinary conditions should not bar' mere than eighteen hours, because of risk of alteration in the layer of emulsion. The best method of drying vegetable substances (leaves, .etc.) before placing them in contact with the sensitive plate is 'to put them between two sheets of very white blottingpaper and subject therh to a pressure pf 200 to 1000 kilogrammes, to the square metre (40 to 200 pounds per square foot). This pressure expels the sap, and the leaf may be placed in contact with the photographic plate after an instant's exposure to the air. To know whether pressure should be repeated, and whether it should be 20, 40, or 60 pounds, there is no better way than to compare the results'of pre-

vious experiments, having reference to the ■thiokness of the leaves, their degree of moisture, etc. This drying process has the advantage of giving a double image; that is to say, a, direct image of the dried leaf and an indirect image toy contact with the blotter impreignated with the sap, for the liquid . . . may itself react on the sensitive him. . . When there is a great deal of sap the action is generally more intense. When a leaf is dried its action is considerably weakened, and may become absolutely null. -The power of the leaf resides irregularly on different parts of the surface, but in- very old dry leaves a certain amount of the active principle always remains." Petals, the writer goes an to say, may be -used in the same way as leaves, and the color of the petal makes no difference. The pistil of a flower is very- active, but the pollen alone gives no results. The first leaves of a sprouting bean do not act on the plate, but when the plant has attained some degree of growth the leaves act as usual. -The same is" true of other seeds and nuts, such as the acorn, chestnut, pea., almond, barley, etc. In bulbs the plant germ is inactive, but the envelopes are partly active. When growth begins the germ becomes active also, -but in different degrees with various plants. The activity of roots is also considerable. In this way Russell has tried almost every form, of vegetable tissue. What can be the cause of this photographic action and why should it vary 'so greatly from one .kind of tissue and from one stage of growth to another? It is evident, the writer says, that radioactivity can have nothing to do with it, for the object must be in actual contact with the plate : even the thinnest sheet of glass or of mica arests all action. ■ Sir Combes goes on : —"Russell advances the hypothesis that the active substance is peroxid of hydrogen. By dissolving one part of pure peroxid in one million parts of water, we may obtain a solution susceptible of acting on a photographic plate at the end of twenty-four hours, even when the sensitive layer is kept at a distance of 3 millimeters (£in) from the surface of the liquid. Mr Russell recalls the fact that Usher and Priestly, among many other observers, affirmed that formaldehyde and peroxid of hydrogen are the first products of the growth oi'plants. This would explain the action of growing plants on the photographic plate. • On the other hand, the resins ana turpentine''are common in certain plants-, and even in very small quantities these may give rise to hydrogen peroxid. This is the hypothesis that is now open to .verification or disproof by other experimenters."