194 LIFE AND WORK OF SIR JAGADIS C. BOSE 



cases chosen as typical the various factors which are 

 predominant, as notably the response (i) to variation of 

 temperature, (2) to variation of light, and (3) to the varia- 

 tion geotropic response under daily variation of tem- 

 perature. This last phenomenon, hitherto unsuspected, is 

 the determining cause of a very large number of day and 

 night movements. In many instances the resulting effect 

 is due to different combinations of various factors. Light 

 and heat may be strong or weak ; moreover, radiant heat 

 has quite the opposite effect to that of mere raising of 

 temperature ; light may give rise to after-effects, and the 

 plant's responses may also vary from simple to more or 

 less multiple and automatic. Thus the independent 

 variables are many. Calculation shows the possible 

 variety of effects to be enormous, and observation in- 

 creasingly shows that nature has realised no small number 

 of these. Bose's demonstration of the reaction in typical 

 cases will enable the inquirer to predict the effect of 

 combination of different factors. 



His success in these investigations is due to the 

 perfection of his newly invented apparatus by which the 

 movement of the plant becomes automatically recorded 

 throughout the day and night. The periodic variation 

 of environmental conditions is also recorded at the same 

 time by his thermograph and recording photometer. 

 Confirmatory experiments are carried out where light 

 is maintained constant, the plant being subjected to the 

 daily variation of temperature ; in others the temperature 

 is maintained constant, and it is the diurnal change of 

 light and darkness that affects the plant. The results of 

 such protracted investigation enabled him to unravel the 

 complexities of the daily movement of different plants. 

 The following extract from Bose's popular lecture given 

 at his Institute will be found interesting as regards the 

 ' sleep ' and ' waking ' movements of the water-lily 

 Nymphaea, and the investigation which led to the discovery 

 of the cause of this movement. 



