[Illustration: FIG. 87.--Effect of rise of temperature on pulsation of leaflet of _Desmodium gyrans_. Horizontal line represents the duration of gradual rise of temperature from 30°C. to 35°C. Note the expansive effect of rise of temperature in reduction of systolic limit of pulsation.]
_Effect of rise of temperature on pulse-record: Experiment 93._--In studying the effect of rise of temperature on the pulsation of leaflets of _Desmodium_, we discover similar antagonistic reactions of light and warmth. The leaflet was placed in a plant-chamber with an electric arrangement for gradual rise of temperature. The first two 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.
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.