Page:Life Movements in Plants.djvu/268
records were taken in the normal temperature of the room, which was 30°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 diametrically opposite to that of light. The record in Fig. 86 exhibited the contractile effect of light by reducing the diastolic limit of expansion. In 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 allowed to return to 30°C., and we observe the gradual restoration of normal systolic limit of contraction.
SUMMARY.
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 Desmodium 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 the retardation of growth, but also by the characteristic modification 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 Desmodium the contractile effect of light induces a rapid diminution of the diastolic limit of expansion, while the expansive reaction of warmth brings about a marked reduction of the systolic limit in successive pulsations.