Page:Popular Science Monthly Volume 2.djvu/316

From Wikisource
Jump to navigation Jump to search
This page has been validated.

the whole inner surface of the cell; sometimes the quantity is smaller, and they are separate. Now, it has lately been discovered that in the latter case, under the influence of light, the green corpuscles we speak of undergo very singular changes of position. Some twelve years ago, Boehm noticed for the first time that in certain unctuous plants the grains of chlorophyll gather at one point of the wall of the cells under the action of the sun. He remarked that the phenomenon does not take place in the dark, nor in the red rays. The flat sheet made up of a single layer of cells, without epidermis, which composes the leaves of mosses, seemed to Famintzin the most suitable for this delicate kind of observations. He followed the movements, that take place in these sheets, by microscopic study. During the day the green coloring-grains are scattered about the upper and lower parts of the leaf-cells. At night, on the contrary, they accumulate toward the lateral walls. The blue rays affect them like white light; the yellow and the red ones keep the chlorophyll in the position it takes at night. The order of activity in the rays seems, then, to differ in this case from that in the phenomena of respiration. The researches of Borodine and Prillieux proved that these movements of coloring-corpuscles within the cells occur in almost all cryptogamous plants, and in a certain number of phanerogamous ones. The lately-published experiments of Roze show that in mosses the grains of chlorophyll are connected by very slender threads of plasma, and may suggest the idea that these threads are the cause of the changes of position just described. Perhaps there is some real relation between them; but it must not be forgotten that these movements of the plasmatic matter inside the cell take place by day and night, and that light has no marked effect on them. The green particles, on the contrary, creep over the walls of the cell, and move toward the lightest part as zoospores and some infusoria do.

Biot relates that in 1807, while at Formentera, employed in the work of extending the meridional arc, he devoted his leisure hours to the analysis of the gas contained in the swimming-bladder of fishes living at different depths in the sea. The oxygen required for these analyses was furnished him by the leaves of the cactus opuntia, which he exposed in water to sunlight, under hand-glasses, ingeniously applying the discovery of Ingenhousz and Senebier. It occurred to him one day to expose these leaves, in a dark place, to the illumination thrown by lamps placed in the focus of three large reflectors, used for night-signals in the great triangulation. He threw the light from three of these reflectors on the cactus-leaves. The eye, placed in this concentration of light, must have been struck blind, Biot says. The experiment, kept up for an hour, did not cause the release of a single gas-bubble. The glass was then taken into the diffused light outside the hut. The sun was not shining, but the evolution of gas took place at once with great rapidity. Biot is a little surprised at the result and