XLV.— ON THEKMO-GKOTROPISM . 



By 

 Sir .7. (\ Bose. 



I SHALL in this chapter investigate the efl'ect of vari&- 

 tioii of temperature on geotropic response. We have to 

 hear in mind in this coDuection, that for the exhihition of 

 geotropic curvature two conditions are neces.-ary : (1) the 

 presence of a perceptive organ to undergo excitation iinder 

 the stimulus of gravity, and (2) the motility of the 

 orjfan. A motile organ, including both the pulvinated and 

 growing, will exhibit no geotropic effect on account of the 

 depression of the power of perception through seasonal or 

 other changes, or in the entire absence of the perceptive 

 organ The organ may, on the other hand, possess the 

 geo-perceptive apparatus, but no visible movement can take 

 ))lace in the absence of motility of the tissue. 



As regards the modifying influence of temperature on 

 g.'otropic curvature, the efl'ect will depend on two factors: 



(1) the influence of variation of temperature on geo- 



perception by the sensitive layer, and 



(2) the modifying efTect of tt-mperature variation on 



the motile reaction, 



I havH in Chapter XLIII adduced facts which appear to 

 show that the power of geo-perception declines at high 

 temperatures. As regards motile reaction, we have seen 

 that in Mimosa it increases from a minimum to an 

 optimum temperature beyond which there is a depression 

 (p. r)5). As the optimum temperature for geo-perception 

 is not necessarily the same as that for responsive curva- 

 ture, the result is likely to be very complex. 



