Page:Life Movements in Plants.djvu/268

238 records were taken in the normal temperature of the room, which was ;?0°C. The temperature was gradually raised to 35°C, the record being taken all the time. It will be seen (Fig. 87) that the effect of warmth is dia- metrically opposite to that of light. The record in Fig. 86 exhibited the contractile effect of light by re- ducing the diastolic limit of expansion. [u the present case the expansive reaction of warmth is exhibited by the reduction of systolic limit of contraction. The temperature of the plant chamber was now al'owed to return to 30^0,, and we observe the gradual restoration of normal systolic limit of contraction.

Two different effects are found in the action of the stimulus of light alike on the autonomous activity of leaflet of Desmodium gyrans and of growing organs. In condition of sub-tonicity light renews pulsation of Desmo- dium and enhances the activity of growth. In normal tonic condition the effect induced is the very opposite, light causing an arrest of pulsation and retardation or arrest of growth.

The contractile effect of light is seen not only in t'le retardation of growth, but also by the characteristic modi- ficaiiou of pulsation of Desmodium in the diminution of diastolic limit of expansion.

The antagonistic reactions of light and warmth are found not only in growth but also in the rhythmic activity of Desmodium gyrans. In the pulsation of Des- modium the contractile effect of liglit induces a rapid diminution of thi diastolic limit of expansion, while the expansive reaction of warmth brings about a marked reduction of the systolic limit in successive pulsations.