3 24 RESEARCHES ON IRRITABILITY OF PLANTS 



the amplitude. This is seen in the following record (fig. 

 i66), where the normal pulsations are modified in 

 consequence of lowering the temperature through a few 

 degrees. 



The following experiment, carried out on the leaflet of 

 Desmodium, shows that the effect of lowering of temperature 

 on it is precisely the same. The temperature of the room 

 at the time of the experiment was 30° C. A record of three 

 normal pulsations was taken at this normal temperature. 



Fig. 166. — Efifect of lowering of temperature in increasing 

 amplitude, and decrease of frequency of pulsation of 

 frog's heart. Series to the left represent normal pulsa- 

 tions at the temperature of room ; series to the right 

 were recorded at a temperature several degrees lower. 

 (Brodie.) 



The specimen was then gradually cooled by sending through 

 the chamber a stream of cold air, the record being taken 

 all the time. The successive dots in the diagram are at 

 intervals of 2 seconds. Hence the period of complete 

 pulsation can be accurately determined. 



It will be seen from fig. 167 that at 30° C. the period 

 of a complete pulsation was 80 seconds, the amplitude 

 being 25 mm. On lowering of temperature to 29° C. the 

 period became lengthened to 88 seconds, the amplitude 

 being enhanced to 30 mm. At 28° C. the period was 



