CHAPTER XII 



EFFECT OF TEMPERATURE 



Temperatures optimum, maximum, and minimum — Diminution of electrical 

 response by cooling — Temporary or permanent abolition of response due to 

 cold — Characteristic differences exhibited by different species — Mechanical 

 response of Biophytum and autonomous response of Desmodium arrested by 

 cold — Prolongation of latent period — Diminution of longitudinal mechanical 

 response by cold — Diminution of electrical response of plants by rise of 

 temperature — Similar diminution seen in longitudinal mechanical response — 

 Increase of excitability due to cyclic variation of temperature. 



ONE of the factors which modify response in plants is 

 temperature. It is known in a general way that certain 

 temperatures are favourable, and others unfavourable, to 

 physiological activity. It is generally understood further 

 that there is a certain optimum, in the case of each species, 

 above or below which the excitability of the plant undergoes 

 diminution. After this, on reaching a certain maximum or 

 minimum temperature, as the case may be, excitability is 

 abolished, and if these unfavourable conditions be long main- 

 tained the plant is apt to be killed. But the problem of the 

 precise determination of such points has hitherto offered 

 insuperable difficulties. 



Effects of cold : (a) Diminution or abolition of electrical 

 response. — Already, however, by adopting the electrical mode 

 of investigation, I had been able to overcome these difficulties ; 

 for I had found that the amplitude of the electrical responses, 

 under different temperature-conditions, afforded a means of 

 measuring the excitability of a tissue at the respective points. 

 And now, by the use of mechanical response, I am enabled 

 again to investigate the same problem by new and indepen- 

 dent means. From the results obtained it will be seen that 



