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342

Circumnutatio

Periodicity of Leaves

The very common bushes general many of the leaves with [evening]

we may infer that a slight daily rise in the evening & at night is [illeg] common, perhaps general, with growing leaves at least with those not provided with a pulvinus. We have indeed as yet failed to discover any leaves which fall only a few degrees at night (for sleep-movements are here excluded) though we are far from assuming that some such do not occur.)

(On the Periodicity of the movements of Leaves & Cotyledons.— It was shown in the    Chapter that exactly the same phenomenon is extremely common with cotyledons

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Frank

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[in margin:] Probably temporary turgescence on upper side not [illeg] by [illeg] & so

special manner, so as to resist the action of light when coming directly from above, in order that they may retain during the day whatever position is best filled for their functions. How this resistance is effected, whether by greater growth on the upper or less on the lower surface than would otherwise would naturally might have been expected occur under such circumstance illumination, we do not know. But we can see that the resistance modification of the circumnutating movements must be of a nightly