210 chap. xxiii. photosynthetic increase of weight 



Summary 



There are various sources of error in the determina- 

 tion of photosynthetic increase of weight by the half-leaf 

 method, as also by the method of intake of carbon dioxide. 



The new method measures the photosynthetic increase 

 of weight in the living plant during exposure to light, either 

 by means of a sensitive Torsion Balance or by a Chemical 

 Balance. 



The advantages of the new method, which is direct, are 

 (i) the natural conditions of the experiment ; (2) the elimina- 

 tion of loss of weight due to transpiration, and to trans- 

 location of carbohydrates. The accession of mineral as 

 well as nitrogenous substances from the soil is also avoided 

 in experiments with cut specimens. 



The weight is found to increase with the intensity of 

 the light and the duration of exposure. The formation of 

 carbohydrate under sunlight is about five times greater 

 than that under diffuse light from the sky. 



The maximum rate of formation of carbohydrate in 

 Hydrilla under perpendicular incidence of sunlight is 

 2*8 grm. per hour per sq. metre. 



