28 CHAP. IV. AUTOMATIC RECORD OF EVOLUTION OF OXYGEN 



these essential details ; but the saving of time and labour 

 in the experiment, the elimination of complicating factors 

 for correction, the directness and accuracy of the results, 

 are features which cannot even be approached by any other 

 method. This will be quite evident from a typical ex- 

 periment described below, which also explains the method 

 of procedure. 



A vigorous specimen of Hydrilla was mounted in the 

 bubbling apparatus with the Electromagnetic Recorder. 



Fig. 4. Records of successive evolution of equal volumes of 

 Oxygen under Constant Tight 



The three records were obtained at the commencement, after 

 twenty minutes and after forty minutes. 



The incident light on the plant was constant, the source 

 being a Pointolite of 100 candle power. The beam was 

 rendered parallel by means of a lens. Records of successive 

 bubbles (of equal volume) were taken continuously for an 

 hour, of which portions at the beginning, after twenty 

 minutes and after forty minutes, are reproduced in fig. 4 ; 

 the responses are seen to be practically uniform throughout 

 the hour. Independent observations were also taken of the 

 periods of successive bubbles, with the help of a metronome 

 beating seconds. Table III. gives the detailed values of 

 the successive periods. 



