144 



PLANT RESPONSE 



tional has to be effected, namely, the acceleration of growth. 

 We may therefore expect that the optimum temperature 

 for growth will be relatively higher than that of simple 

 response. And this I generally find to be the case. When 

 the temperature is much raised, the electrical response of a 

 plant is seen to undergo diminution (fig. 78). It is to be noted 

 that the temperatures referred to are dry, or atmospheric only. 

 This explains why, even when the temperature was raised to 

 65 C, which is above the fatal point, response was still 





20°C 



30 °€ 



uut 40 o C S0T 65 o c S 5°c(w) 



FlG. 78. Effect of Rise of Temperature on Electrical Response 



observed. Owing to the relative non- conductivity of the 

 plant, and the evaporation from its surface, the tissue does 

 not actually attain the temperature of the surrounding air. 

 When, however, it was subjected for some time to a water- 

 temperature of 55 C. response disappeared, by the death of 

 the specimen. 



(J?) On longitudinal mechanical response. — I give next 

 (fig. 79) the effect of rise of temperature on longitudinal mecha- 

 nical response. The specimen was a 

 filament of the corona oi Pas si flora, 

 the stimulus used being thermal. In 

 order to subject the plant to definite 

 temperature conditions, the adjust- 

 ments were made by means of a 

 subsidiary heating coil, placed inside 

 the chamber. Any given temperature above the normal 

 could thus be maintained constant, for the required length of 

 time, by simple adjustment of the strength of the heating 

 current. The results thus obtained in mechanical response 



Fig. 79. Effect of Rise of 

 Temperature on Longi- 

 tudinal Contractile Re- 

 sponse of Plant 



