— 225 — 



occurs through the tube c and the expulsion of air through 

 the tube d. This is attained by means of two Y pieces of glass and 

 two twoways cocks, connected as the figure shows. When the 

 vessels are shifted, the glass cocks are simultaneously turned 

 through 180° and the air current will continue to go through the 

 tube c. 



The air current is passed first through the plant receiver 

 (E). The form of the plant receiver varies much according to 

 the leaves that are employed for the experiment. Conical flasks 

 (vol. 50 — 100 cm 3 ) are convenient for small plants with rosette 



Fig. 1. Apparatus for estimation of G0 2 assimilation and respiration. 



leaves, flat glassboxes, flat retorts or glass tubes for single leaves. 

 Care should be taken that the quantity of air contained in the 

 plant receiver is as small as possible. The leaves in the glass-boxes 

 are fixed on a wire grating. The leaf stalk is placed in a small glass, 

 made in the form of a retort from glass tubing with a diameter 

 of 1 mm, to supply the leaf with water during the experiment. 

 The width of the openings of the stomata may be estimated after 

 the method of Molisch. 



From the plant receiver the air current passes through the 

 absorption apparatus (D) 1 ), consisting of 3 — 4 test tubes (length 18 

 cm, diameter 12 mm), the form of which is shown in the fig. The 

 air is conducted through capillary tubes, which are pressed against 

 the bottom of the test tubes, so that the air passes through 

 the absorbing liquid in very small bubbles. 



In my first experiments the plant receiver was fitted in between 

 the shifting apparatus and the absorption tubes and the air 

 current was passed under pressure through the apparatus in the 



*) Another absorption apparatus that also could be used in these experi- 

 ments is described by Warburg (1909). 



