arc-lamp with self-regulating arrangement for securing steadi- ness of light, and (2) an incandescent electric lamp: 'l‘wo inclined mirrors were placed close behind the specimen so that it should he acted on by light from all sides.
NORMAL EFFECT OF LIGHT.
lat-perimmt 78.——-l shall first give records obtained with Kymmr on the action of light. The first series exhibits the normal rate of growth in darkness; in the next the retard- ing etl'ect of light is set-n in the shortening of spacings, as compared with the normal, between successive dots. The light was next cut oil and record taken once more. after half an hour. .irowth is now seen to have recovered its normal rate (Fig. With regard to the after- etl'ect of light I may say in anticipation that there are two tlitl‘erht results, which depend on the physiological condition of the tissue. In a tissue whose tonic condition is below par, the aftercctl'ect is an acceleration; but with tissues in an optimum condition, the immediate al'ter—ell'ect is a retardation of the rate of growth. This is specially the case when the incident. light is of strong intensity and of long duration.
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FIN 75. ~-Norm:tl ell‘et't. of light. N. Iml'mill ; S. retarded late of growth in response
to light :'N, recovery on cessation of light.
DETERMINATION OF THE LATENT PERIOD.
There is a general impression that it takes from several minutes to more than an hour tor the light to react on the growing organ. 'l‘his underestimate must have been
