become circumscribed, and the intensity and duration of
stimulus necessary to convert the positive to negative will
he fechlcr and shorter. It will he very seldom that a
plant is likely to he found at the optimum. Hence
plants in general may he expected to give a feeble positive
reSpmme under sub-minimal stimulus.
'l‘hvse considerations led me to look for the positive respmme under sub-minimal stimulation; the tracings which I have obtained with my highly sensitive Cresco- graph and other recorders show that my anticipations haVe been justilied.
Positive res/mm- under sub-minimal stimulus: Erperi- mrenl. elm—In normal specimens, lightof strong intensity in- duces a retardation of growth. When the source of light is placed at a distance, the intensity of light. undergoes great diminution. Under the action of such l‘eehle stimulus I obtained an :wceleration of growth even in specimens which may he regarded as moderately vigorous (lt‘lg. *3). Similar acceleration of growth was also
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Fin. S.i-~\i'i'i'li-ratinn of growth under sub—minimal llg'nt stimulus ltci‘nrll on moving plate: stimulus applied at 5th dot. and sulM-qurut erection of cuer exhibits acceleration of growth. l.a.~t part of curve shows recovery of normal growth on ccsmtiun of SLlUlltlllr.
