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turning. So, again, if we place as a screen a green solution of chlorophyll between the plant and the light, so as to cut off the rays that are absorbed by chlorophyll, then no turning takes place, although the other rays pass through quite freely to illuminate the plant.
A further piece of evidence in favour of the view that it is the light absorbed by the chlorophyll grains that sets up the stimulus is found in the fact that in many plants, the chlorophyll corpuscles are themselves, under the influence of too strong or too weak a light, brought into more suitable positions in relation to the light either by being turned completely round so as to present a greater or less surface to it, or by being moved into different positions in the cell. As soon as the chlorophyll grains are in the right position
. the movement stops, and the stimulus to movement must also have ceased. It is the same in the turning of the leaf. So long as the leaf is in an oblique position with respect to the light, the chlorophyll grains are unequally illuminated and the chemical changes thus set up in any individual cell are unequally distributed. As soon as the leaf-blade reaches its most advantageous light position, the light falls in such a way as to illuminate the chlorophyll grains equally, the chemical changes are also equalised, and the stimulus to movement then ceases. When the light falls upon the chlorophyll grains, the chlorophyll is probably decomposed, and this is indicated by a slight bleaching which takes place. This is not normally visible in the leaf, as a reconstruction of the chlorophyll takes place immediately and the green colour is maintained. But if the action of an intense light on the leaf is prolonged for some time, or if leaves which are ordinarily found in the shade are submitted to a strong light, the bleaching of the chlorophyll goes on more rapidly than its reconstruction, and the leaves become visibly paler in colour. So, also, if the chlorophyll is removed by dissolving it in methylated spirit, the green solution rapidly becomes bleached on exposure to light. This process of bleaching is the result of profound chemical changes which take place in the chlorophyll, and it is very probable that they are quite sufficient to originate the stimulus by the transmission of which the movements of the leaf are modified.
Practically, we know nothing more than this of the causes which bring about the perception of light in an animal eye. When the image formed by the lens of the eye impinges upon the retina (a delicate but highly organised pigmented layer of nervous elements VOL. XXXIV.-NO. 203, N.S.
at the back of the eye) changes take place, whether chemical or physical is not clearly understood, by means of which a stimulus is set up and conducted by the optic nerve to the brain. In many vertebrates there is found, associated with the percipient organs of the retina, a substance called visual purple, which is possibly derived from the pigment layer, and has some rather striking analogies with chlorophyll in its behaviour towards light. The function of the pigment in the animal eye is still unknown and the comparison cannot therefore be carried very far. .
It is not probable that light is usually the originating cause of movements in plants. C. and F. Darwin showed that plant organs such as leaves, stems, tendrils, &c. have a movement of their own (circumnutation, it is called) set up by changes originating within themselves without direct reference to external conditions. These movements are continually going on, and their discoverers suggested that the movements towards the light are all modified forms of circumnutation. That is to say, the light does not actually set up the movement, but exercises a directive influence upon movements which are already taking place. To quote from their paper on The Power of Movement in Plants':
A plant, when exposed to a lateral light, though this may be bright, commonly moves at first in a zigzag line, or even directly from the light; and this no doubt is due to its circumnutating at the time in a direction opposite to the source of the light, or more or less transversely to it. As soon, however, as the direction of the circumnutating movement nearly coincides with that of the entering light, the plant bends in a straight course towards the light, if this is bright.'
This is perhaps as far as our present state of knowledge will take us in this intricate subject. We have seen that leaves are provided with lenses capable of focussing the light that falls upon them among the chlorophyll grains just below the skin of the leaf, that these grains move under the influence of light and suffer chemical change. We also know that reaction to the light received by the leaf-blade or in the upper part of the leaf-stalk takes place in another part of the leaf-stalk, so that we have clearly a reception and transmission of stimulus. gested that this stimulus is set up by the chemical action of the light upon the chlorophyll, and that it continues so long as the chlorophyll grains are unequally illuminated. One reason for this supposition is that if we analyse (by means of a prism) the
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light that falls upon the plant so as to split it up into the various colours of which it is composed, we find that it is the blue and violet rays especially which are active in promoting movement, and the blue and violet rays are both strongly absorbed by chlorophyll and capable of decomposing it.
The final conclusion at which we arrive is, therefore, that although plants may not perceive (as we understand the word) the images which can be formed so perfectly in their epidermal cells, nevertheless they have a contrivance that enables them to distinguish light from darkness and to respond thereto. It is not suggested that plants feel in the same way that animals do; all that
; we can say is that internal activities of the plant are so closely bound up with external stimuli, that the plant is constrained to move in a given direction until there is harmony or equilibrium between the two. The more we study the activities of plants in relation to the external world, the more clearly does it appear that the stimulation of the living substance of the plant which results in its response to external forces is certainly on a lower plane, but probably only different in degree and not in kind from the stimulation of the much more highly organised nervous tissues in animals.
BY M. EDITH DURHAM.
The sun glared fiercely on a dazzling wilderness of rock, that beat back the heat in great waves till all the mountains reeled and whivered in swirls of hot air.
In a shadow like an ink blot, cast by a little crooked oak, sat Hil, crouched on his heels, and stared miserably at a parched patch of earth, whereon rows of half-grown maize were shrivelling, all yellow, in the sun.
Poor little field, hacked by a hoe, scattered with seed and harrowed by a bundle of brushwood weighted with a stone. The weary hours that had gone to the making of it were all in vain. Inch by inch had Hil and his brother pounded holes in the rocks with a crowbar, rammed them with powder, and piled the resultant fragments round in a rude wall. Countless little sackfuls of earth had they collected and carried. And now all hope of bread for the winter was gone.
The heavy blue sky closed down like a lid on the aching land. No cloud brought hope; not a leaf stirred; nor was there any sound save the wailing bleat of five sheep that crowded into the shadow close to Hil, striving to escape the sun's rays.
Man and sheep were scarce distinguishable. Hil's ragged chakshirs were of home-spun undyed sheep-wool, and the only garment on his back was a sheepskin coat. The shining row of brass cartridges in his belt was his sole distinction.
The sheep gasped and panted. They had drunk no water since the night before-every well and spring was dry. Hil's sufferings were greater even than theirs. He shook with fever, contracted last time he was on the plains, and he had the added misery of a hopeless future.
It was useless to stare at the maize. He rose to his full height of not much more than five feet; for he was one of the little dark hill-men whose forefathers fought the Romans, in the days when the land was known as Illyria.
Shifting the long strip of dirty cotton that bound his shaven head, so as the better to protect it from the sun, he crossed from
the shadow to his hovel, which, built and roofed with slabs of unhewn rock, merged almost invisibly into the stony wilderness.
'Water !' he said ; 'give me water.'
A ragged woman, wearing a stiff bell-shaped skirt woven of black sheep's wool and worked in curious devices, rose wearily, as was her duty when the zoti i shpis (house-lord) entered. She tucked her distaff under one arm and went on spinning a coarse wool thread with a dexterous twist of her fingers.
* There isn't any,' she said. And as she spoke she took Hills Martini, which he unslung as he entered, and hung it to a peg of projecting stone.
Why isn't there any ?'
The child, a sickly boy of about nine, lay on a heap of dry fern in one corner, too listless to drive away the flies that swarmed on his face and filthy rags.
Gjoko was not Hil's son. Hil had inherited his elder brother's widow as wife and adopted his child. Drana had passed from one brother to the other as a matter of custom and convenience. The priest, after vainly protesting, had excommunicated the couple. But the church was an hour distant, up the mountain-side, and tribe-law was more binding on Hil than church-law.
Moreover, in no other way could Hil have obtained a wife. For he was a very poor man, and wives, in the mountains, have to be bought with money. And the present comfort of possessing a woman far outweighed the vague possibility of Hell in the future.
He picked up the flat-shaped water-barrel that Drana had carried up before sunrise from the shrunken yellow Drin that flowed in the valley nearly two thousand feet below.
But the little barrel gave forth no answering rattle. He pulled out the maize-cob plug. But no drop flowed.
He sat down heavily on a block of tree-trunk by the side of the hearth-stone, rolled a cigarette, and poked vainly for a spark in the gray heap of wood-ash, over which hung an empty cauldron. Finally, with a flint and steel, from the leathern pouch at his belt, he kindled the cigarette and smoked his very last pinch of tobacco in silence.
Then he said : The maize is all dead.'
I know. Why did you sow it all? Why did you not keep some to eat ?' asked Drana, spinning ceaselessly, like one of the Fates.
'How was I to know there would be a drought? We had a