Mast, Samuel Ottmar, 1871- · New York, J. Wiley · leaf 173
ydra to remain oriented maythen be the result of stimulation by constant intensity,there is no evidence whatever that light acts constantly asa directive stimulus. Light may however affect locomotionby acting constantly, much as temperature does; but evenin this case it is impossible to be certain… … n
Light -- Physiological effect · Phototropism
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