366 AN AUTUMNAL THOUGHT. the Molluscs, and for our grand whole we have a minimum of half a million of ANIMAL SPECIES! This is the very figure, observe, at which we arrived as representing the lowest limit of the totality of VEGETABLE SPECIES, living and moving, flourishing, and dying, and reproducing, on the surface of the globe. We leave the reader to meditate-as meditate he surely must-on the sublime thoughts, the overpowering ideas of Power and Wisdom which these considerations suggest. WHAT IS CHLOROPHYLL? We are drawing towards the close of autumn; we shall soon be in sight of the "melancholy days of the year;" when, for a while, the "voice of the turtle" will cease in the leafless groves, and the banks and braes will be sadly bare of their floral garniture. As yet, however, the trees retain their glorious vesture, though streaked and varied with the gorgeous colours of decay; and in the sheltered corners of the woods, on the sunny southern slope of the grassy hill, and beneath the covert of the still fragrant hedgerow, many a blossom appeals to our souls with its promptings of sweet images and tender fancies. The arum still raises its clusters of deep-scarlet berries, and spreads its spotted leaf "Armed with keen tortures for the unwary tongue;" the blue-bells hang their delicate cups among the thick herbage; and the wild marigold contrasts its yellow splendour with all this crimson and azure magnificence. The daisy, SWEET THINGS STILL LEFT. 367 too, has not forsaken us-sweet shield of silver, embossed FIG 78.-"As yet, the trees retain their glorious vesture.' with gold!-but brightens still the pleasant meadow and the sloping bank. 368 WHAT IS CHLOROPHYLL? "The rose has but a summer reign, The daisy never dies;" and though it first makes its appearance in the merry springtime, and is truly a child of the early year, it lingers on to become a precious ornament of our scanty autumn wreaths. Sweet flower of song!-dearer to the poet than even lily or violet-who does not remember, and remembering feel, all the pathos of the dying exclamation of poor Keats,—“ I feel the daisies already growing over me!" They heighten the commonest and cheer the saddest corners of the earth, and are ever ready, in their simple loveliness, to awaken thoughts of grateful tenderness and love— "So glad am I when in the daisy's presence, That I am fain to do it reverence." To what do the leaves, now changing their hues so rapidly, and varying through all the tints of purple, brown, and yellow, -to what do they owe their normal colour, the fresh, vivid, beautiful green? To a substance called chlorophyll-(xλwgds, green, and quλλov, a leaf). Well, what is chlorophyll? The colouring matter of plants, which, accompanied by grains of starch, floats like very minute seeds in the fluid of their cells. In some respects it is analogous to wax; it will not dissolve in water, but is easily affected by ether or alcohol. Chlorophyll is dependent upon the action of light, if not for its formation, at all events for its development. Keep a plant in a dark room or cellar, and it will become blanched SOME RECENT EXPERIMENTS. 369 and sickly; the colouring matter dries up, and the white, wan tissue of the leaf is all that survives. The more a plant is exposed to the light, the deeper will be its green. In a shrubbery you may notice that the brown leaves of any particular evergreen or bush, if so situated as to lose the direct action of the sun's rays, will soon change colour. Instead of their natural brightness of tint, they assume a sickly greenish-yellow hue, and are said to be suffering from chlorosis. The formation of the chlorophyll is obstructed, or takes place too slowly. Of course, this peculiar condition will frequently arise from bad soil, or a long continuance of damp weather; but it is also the result of a want of light. It should be observed that young leaves are always of a lighter green than old; simply because the latter have been exposed for a longer time to the light. And so the leaf goes on deepening and deepening in colour, until the sad days of autumn come, and the green gives way to yellow and brown and red, owing to the influence of the changing season on the chlorophyll of the plant. In reference to this interesting subject,-which deserves to be more closely investigated,-we may place before the reader the results of certain recent experiments.* MM. Prillieux, Brongniart, and Roze (Comptes Rendus, Jan. 3 and 17) have made some important observations on the apparently spontaneous movements of the grains of chlorophyll within the leaves of plants. These had been observed by Böhm to congregate under the direct action of the sun; * As recorded, in a condensed form, in The Academy (Feb. 12, 1870), pp. 131, 132. 370 A PLASMIC ILLUSION DETECTED. Famitzin, confirmed by Borodine, had also recorded very marked movements in the leaves of a moss under the influence of light. This class of plants offer great facilities for these observations, inasmuch as the movements can be observed in them under the microscope without dissection, M. Prillieux kept a moss in the dark for several days, when the cells presented the appearance of a green network, between the meshes of which was a clear transparent ground. All the grains of chlorophyll were applied to the walls which separate the cells from one another; there were none on the upper or under walls which form the surfaces of the leaf. Under the influence of light the grains change their position from the lateral to the superficial walls; under favourable circumstances this change takes place in about a quarter of an hour. On attaining their new position, the grains do not remain absolutely immovable, but continually approach and separate from one another. If again darkened, they leave their new position and return to the lateral walls. Artificial light produces the same effect as daylight. M. Brongniart further observed that this movement of the chlorophyll, under the influence of light, does not consist in the change of position of isolated grains, but of masses of net-work, each containing a certain number of grains. In addition, M. E. Roze states that, besides the grains of chlorophyll which coat the walls of the cell, each cell is lined with a transparent mucous plasma formed of very fine threads, the extremities of which unite together the grains of chlorophyll. This protoplasm exhibits, under a high magnifying power, a very slow motion, |