2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 87 



offer an interesting basis for the comparison of photosynthesis in 

 higher plants with his observations on algae. A discussion of this 

 comparison will be taken up in connection with our experimental data. 



GROWTH CHAMBER AND CONTROL EQUIPMENT 



The problem of controlling the various factors affecting the rate 

 of photosynthesis is somewhat simplified by construction of a growth 

 chamber designed for tall slender plants such as wheat, which can be 



Fig. I. — Diagram of plant growth chamber (G) with auxiliary control systems. 



confined in a narrow tubular space. The simple form of the apparatus 

 depends to some extent on the fact that the plants are grown in nutrient 

 solution. A general view of the apparatus is shown in Plate i. 



Figure i is a diagrammatic drawing of the growth chamber and the 

 necessary auxiliary apparatus for controlling the air-carbon dioxide 

 supply, temperature, and humidity. The light intensity was controlled 

 by the number, size, and distance of the incandescent lights placed 

 symmetrically around the growth chamber. 



The growth chamber, G, consists of a double-walled glass tube about 

 90 cm long and 2.6 cm inside diameter with the inner tube extending 

 about 5 cm below the seal with the outer tube. The inside diameter of 



