STUDIES IN PLANT RESPIRATION AND PHOTOSYNTHESIS. 



23 



2. The Apparatus. 



The determinations of the rate of respiration were made on the 

 principle of drawing air free from carbon dioxid over the leaves 

 and absorbing the carbon dioxid given off by the leaves in a stand- 

 ardized solution of barium 

 hydroxide. The appara- 

 tus was so arranged that 

 the leaves were always 

 under the pressure of the 

 atmosphere. A small pis- 

 ton-pump driven by an 

 electric motor drew the 

 air through the entire ap- 

 paratus; a large reservoir 

 and a pressure regulator 

 assured the regularity of 

 the stream. The air was 

 drawn from out of doors 

 in order to avoid the pos- 

 sibility of deleterious ef- 

 fects from impurities in 

 the air of the laboratory. 

 It was passed first through 

 a train of soda-lime tubes 

 to remove the carbon di- 

 oxid and then through a 

 coil of metal tube, 10 feet 

 long, which was immersed 

 in the water thermostat. 

 A large Freas electric ther- 

 mostat was employed and 

 set at exactly 25°. From 

 the metal tube the air 

 passed to the upper open- 

 ing of the respiration 

 chamber. 



A drawing of the respi- 

 ration chamber is given 

 in figure 1. This con- 

 sists essentially of a gal- 



vanized-iron can 40 cm. deep and 18 cm. in diameter. A heavy 

 lead base permits the entire chamber to be submerged in the 

 water of the thermostat. To the top of the chamber is sol- 

 dered a collar which forms a trough. Into this trough fits loosely 



Figure 1. 

 Respiration chamber with mercury seal and cover, with 

 broken out section showing container for nutrient solu- 

 tion and device for holding petioles of leaves. 



