— 224 — 



found that the intensity of the G0 2 assimilation in this plant is r 

 on an average, 5.6 — 8.8 mg C0 2 per 100 cm 2 per hour, a similar 

 value to that found by Gilt ay. 



I also made several assimilation experiments with an appa- 

 ratus, described in my paper cited above. In this apparatus the 

 air current was produced by the help of an aspirator. The air 

 passed first through a Wulff's flask with KOH solution in order 

 to absorb the C0 2 in the atmospheric air. In this flask a thistle- 

 funnel was fitted, and the supply of air was regulated in such 

 a manner, that the surface of the liquid in the thistle-funnel was 

 constant; hence also the speed of the air current will be constant. 

 Afterwards the air current passed through a conical flask with 

 cotyledons of germinating peas, where the G0 2 content becomes 

 greater than in atmospheric air; next through the leaf receiver 

 and last through a tube with very dilute KOH solution, coloured 

 with Phenolphthalein. In order to determine the intensity of 

 assimilation the time in which the KOH solution was decolorised,, 

 was measured. Also the G0 2 given off by the peas per hour was 

 determined, and the intensity of assimilation could then be 

 calculated. 



Althought the assimilation experiments with this apparatus 

 are not carried out at the G0 2 content of atmospheric air, I 

 have mentioned these experiments here, because they have given 

 rise to the construction of an other and better apparatus, adapted 

 to measure the C0 2 assimilation at the G0 2 tension of atmos- 

 pheric air. 



This apparatus (fig. 1) is based on the same principles as the 

 above mentioned apparatus of Giltay and Brown and Escombe: a 

 current of atmospheric air is passed through the plant receiver 

 with the assimilating leaf, and the C0 2 that is not taken up by 

 the plant is absorbed by baryta solution and measured by titra- 

 tion. Besides the C0 2 content in the air is determined. 



The air current is produced by two graduated vessels with 

 side tubes, of 1 — 2 1. capacity (A and B), closed by india rubber 

 stops with glass tubes. These tubes are fitted with india rubber 

 tubes as the figure shows. One of the flasks (A) is filled with 

 water and set say 110 cm above the other. The water will then 

 run down into the second and drive the air in this flask out 

 through the tubes b and d. At the same time air from the appa- 

 ratus will be sucked into the flask A through the tubes a and c. 



The tubes a and b are connected with a shifting apparatus 

 C, so arranged that by shifting the flasks the intake of air always 



