no PLANT PHYSIOLOGY. 



ground smooth upon a revolving emery-wheel attached to a water- 

 motor (or a grindstone), they will fit perfectly against the paper of the 

 cover. The advantage of this felt paper is that it allows a practically 

 light-tight joint with the flasks. It is well to bore holes in the sides of 

 the larger pot or pan to allow better ventilation. 



A source of error in the apparatus which must be guarded against is 

 the difference of temperature under the different colors. My tests to 

 determine this show that the difference increases with the intensity of 

 the light. If the light is not direct intense sunlight, the differences are 

 insignificant, and with very bright light the differences may be rendered 

 insignificant by covering the whole with thin tissue-paper. For special 

 work even these differences could doubtless be removed by keeping up 

 a circulation of air through the pots by rubber tubes from each con- 

 nected with an aspirator. 



EXPERIMENT 38. To test this it is only necessary to place soaked 

 oats in covered Zurich germinators or flower-pot saucers, each of 

 which rests in a saucer containing water, and to stand them in 

 darkness in places known to be of different temperatures. (See Note 

 10 of the Addenda.) 



EXPERIMENT 39. Invent a simple method of testing this. 



D. Physical and CJicuiical Processes. 



70. What chemical processes are involved in Growth? 



No experiment is here practicable upon this subject, aside 

 from that already taken up in connection with Respiration 

 (Section 58, Experiment 30). Answer theoretically from your 

 various sources of information. 



We next consider what physical processes are involved in 

 Growth. Of these, its relations to the absorption or release of 

 heat, and its relations to amount of mechanical work as mani- 

 fested in exertion of pressure, etc., occur for investigation. 



71. Is heat either absorbed or eliminated in processes connected 

 with Growth? 



Answer by Experiment 40. 



EXPERIMENT 40. This may be settled by comparing the temper- 

 ature of growing (and, therefore, respiring) with that of non- 

 growing (non-respiring) tissues placed under the same conditions. 

 Fill a three-inch flower-pot with peas soaked overnight, and another 

 like it (for a control) with soaked peas freshly killed by hot water. 

 Invert them both over dishes containing a solution of caustic pot- 



