. Botany of the living plant. Botany. GROWTH AND MOVEMENT 123 the other in darkness, tlie former will show normal growth with a relatively short and compact form, and with expanded green leaves. The latter will show an abnormally elongated stem, while the leaf- blades are small, and the whole plant will be pale in colour. This condition is styled etiolation, and the length of the stem is due to the absence of the inhibitory influence of light. It has been found that the violet rays are the most effective, and that they have a retarding influence almost equal to that of full sunlight. (Fig. 85.
. Botany of the living plant. Botany. GROWTH AND MOVEMENT 123 the other in darkness, tlie former will show normal growth with a relatively short and compact form, and with expanded green leaves. The latter will show an abnormally elongated stem, while the leaf- blades are small, and the whole plant will be pale in colour. This condition is styled etiolation, and the length of the stem is due to the absence of the inhibitory influence of light. It has been found that the violet rays are the most effective, and that they have a retarding influence almost equal to that of full sunlight. (Fig. 85.) It is the want of sufficient light for the normal development that makes plants in crowded greenhouses, or in dwelling-rooms grow " Isggy," with unduly lengthened stems and leaf-stalks. Crowding of field crops has a like effect, and often leads to the " laying " of corn under heavy wind and rain before harvest, the plants being top-heavy and their stems weak. MoVEiMENT IN GROWING PaRTS Any ordinary normal young shoot appears to be growing slowly but steadily forward. If the growth were equal on all sides the advance would naturally be steady, and in a straight line. Under casual •__»<'/'' observation this seems to be the fact. But if the growth be analysed by accurate observa- tion it is found to be irregular. From time to time it is greater on one side than on another. The side where the growth is greater becomes convex, and the other concave. The apex will then appear to turn away from the side of greater growth, and a movement will be the result. Such movements though small are the rule in normally growing miV ifaTins Smith, ^ ,' ', reversed at 8,0 parts. They were first detected by Darwin in seedlings. By affixing a fine glass bristle, bearing at its end a small bead, upright upon the tip of a growing plant, and from time to time marking the position of the bead upon a horizontal glass plate placed above it, he obtained an enlarged record of
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