6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8/ 



freely exposed to the air. Temperatures were usually read three 

 times each day. During the light periods the temperatures were 

 approximately 3.5° C. higher than during the dark periods. The 

 average temperatures are shown in Table 2. 



In this experiment no measurement was made of the rate at 

 which air was recirculated through the chambers. Fresh air was 

 injected into the system at the rate of 15 liters per minute. It 

 should be emphasized that a sufficient rate of air movement in plant 

 growth chambers is very essential. It is true, as has been discussed 

 by Wallace (20), that some plants have been grown for several 

 months in glass containers hermetically sealed. Few plants, how- 

 ever, are suited to such an existence and then only when there is a 

 proper balance of mineral and gaseous elements, temperature, and 

 light in their microcosm. In two previous experiments air was 



Table 2 

 Average air temperatures in the plant groiuth chambers 



recirculated very slowly. Under these conditions the plants were very 

 soon affected with oedema. Numerous frosty-white intumescences 

 appeared on the midribs, petioles and stems. The leaves soon became 

 twisted and contorted and finally gave the plant a wilted appearance 

 as illustrated in Plate 2. Atkinson (4), Orton and McKinney (11), 

 and others have described this disease as due to excess humidity, 

 poor lighting, and overheating. With a low rate of air flow in the 

 growth chambers the conditions are ideal for producing this disease. 

 Further experimentation show-ed that with an air flow of 40 liters 

 per minute per chamber all symptoms of oedema were entirely 

 eliminated. 



Marglobe tomato seeds were placed in the germinator on April 21, 

 1932, and the sprouted seeds removed to the germination net on 

 April 26. Eight days later the young plants whose average height 

 was 2.5 cm were set out in the culture jars and placed in the four 

 growth chambers, four to a chamber. For comparison two groups 



