NO. 24 TIME COURSE OF PHOTOSYNTHESIS — McALISTER 3 



Figure 2 shows a diagram, and plate i a photograph, of the plant- 

 growth chamber, air-conditioning system, and optical absorption tube 

 wherein the carbon dioxide is measured. This tube provides an opti- 

 cal path of about i meter. The growth chamber has a water jacket 

 which provides constant " surroundings " for the plant. The water 

 in this jacket has the same temperature as the incoming air, since it 



Fig. 



-Plant growth chamber and accessory system. 



flows from bath B. Bath A is held 3° C. below B to provide constant 

 humidity. For simplicity's sake the temperature controls in baths A, 

 B, and C (C provides root temperature control) are not shown. The 

 spectrograph used has halite (rock salt) optics and is of numerical 

 aperture about F-8. The vacuum thermocouple (located at the exit 

 slit of the spectrograph and reading on the 4.2-4.3 /t band) and gal- 

 vanometer used provide a sensitivity of from 2 to 5 ten-thousandths 



