METHODS FOR ENHANCEMENT OF SENSITIVENESS 187 



had to be made quickly one after another to guard against 

 the loss of sensibility in a protracted experiment. 



Methods for the Enhancement of Sensitiveness 



In order to obviate the difficulties mentioned, various 

 attempts were made to increase the sensitiveness of the 

 specimen. 



Method of rise of temperature below optimum. — One of the 

 methods which appeared promising was to keep the specimen 

 in warm water at a temperature slightly below the optimum. 

 As this temperature of 28 C. was higher than that of the 

 room, the temperature of the plant- vessel slowly fell, 

 on account of loss of heat by convection and radiation. 

 I attempted to remedy this by placing the vessel within 

 a vacuum-jacket. The device was highly successful in 

 maintaining the temperature constant ; but the increase of 

 photosynthetic activity obtained by this interesting method 

 was not sufficiently great. 



Method of depletion of starch. — From certain experi- 

 mental results it had appeared that an excessive deposit of 

 starch causes a partial inhibition of photosynthesis. It was 

 therefore to be expected that depletion of starch would 

 enhance the sensitiveness of the specimen. To test this I 

 placed various specimens in complete and in semi-darkness, 

 with the result that more or less of the starch disappeared. 

 Partial depletion of starch was found to cause an enhance- 

 ment of photosynthetic sensitiveness. A specimen kept in 

 perfect darkness became insensitive and subsequently died. 

 The maximum period in semi-darkness for optimum 

 sensitiveness was found to depend on the physiological 

 condition of the specimen. Though long investigation would 

 undoubtedly enable us to determine the average duration 

 of the requisite period of semi-darkness, the investigation 

 is for the present postponed, as I have succeeded in dis- 

 covering a more satisfactory method for rendering the plants 

 efficient. 



