TEMPERATURE AND AUTONOMOUS RESPONSES 33 1 



the specimen — whether Desmodium, Biophytum, or cardiac 

 muscle — and also, with similar specimens, on the tonic condi- 

 tion. With regard to the first of these points, we have seen 

 that the autonomous vibration of Biophytum comes to a 

 stop below 29 C. The pulsation of Desmodinvi is said to 

 be arrested at 22 C, but I find that this is a matter which 

 is much modified by the tonic condition of the particular 

 plant. With vigorous specimens I have seen that the vibra- 

 tion may persist even at so low a temperature as \J° C. 

 The thermo-tonic minimum in Biophytum and Desmodiuui 

 thus shows a difference, as already said, of about 12 C. ; 

 and in the case of the frog's heart this is still lower, and is 

 said to be about O C. 



When, again, the specimens are raised to a maximum 

 temperature, the pulsations come to a stop. The tempera- 

 ture at which this takes place depends in part on the 

 condition of the specimen. For example, with the frog's 

 heart, this maximum is sometimes at a temperature so low 

 as 38 C. In other cases, pulsation may be detected even at 

 so high a temperature as 44 C. Similarly, in Desmodium, 

 I have found that the maximum temperature at which arrest 

 took place was sometimes as low as 35 C. ; but in certain 

 specimens it did not occur till 45 C. A plant may, 

 again, be accustomed gradually to high temperatures, and 

 under these circumstances the maximum may be raised as 

 much as 3 C. or 4 C. higher. 



Effect of temperature on period and amplitude of 

 response. — The most marked phenomenon of effect of 

 temperature on automatic pulsations, whether animal or 

 vegetable, lies, however, in the fact that the period and 

 amplitude are both affected. When the temperature is 

 lowered, the amplitude of pulsation is enhanced, while the 

 frequency is diminished. Conversely, with rise of tempera- 

 ture, the amplitude is diminished, and frequency augmented. 

 This is true not only of the pulsations of the rhythmic 

 tissue of Desmodium, but also of those of the animal heart. 

 This is seen in the two following records, where the first 



