6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 97 



and traces of Mn, B. Iron was added as FeS04 to all cultures from 

 time to time as conditions demanded. Because the Mazda lamp was 

 run at about its voltage limit its life was short, and replacements were 

 necessary every 6 or 7 days. The plants were grown for 3 weeks with 

 a daily light period of 18 hours. The added heat from the lamps 

 caused a slight daily temperature fluctuation. The average maximum 

 was 24° C. and the average minimum 21.5° C. This resulted in a 

 change in humidity which averaged 57 and 51 percent for the dark 

 and light periods respectively. As found in previous experiments, a 

 temperature fluctuation is beneficial to the tomato plant. Better 

 growth was obtained by subjecting the plants to a lower dark period 



Table 4. — Radiation measurements at beginning of experiment 6 



Foot-candles with 

 Watts/cm^ small G. E. meter 



Culture ' 



nos. Mazda Mercury Total Mazda Mercury Total 



I and 2 0404 .0013 .0417 2,800 ' 200 3,000 



3 and 4 0172 .0031 .0203 1,200 600 1,800 



5 and 6 0065 .0067 .0132 550 1,000 i,5S0 



Table 5. — Plant data from experiment 6 expressed as averages per plant 



Dry wt. 

 Stem Green wt. gram 



Culture ht. grams 



no. cm Tops Tops Roots Total 



1 17-5 6.6 .529 .139 .668 



2 21. 1 7.8 .671 .174 .84s 



3 18.9 5-6 .463 -091 .554 



4 20.9 6.1 .469 .074 .543 



5 23.5 s-o .384 .074 -458 



6 23.8 5-4 -371 -057 428 



temperature (about 3° C lower) than by maintaining a constant 

 temperature during the dark and light periods. 



The intensity measurements which were made at the beginning of 

 the experiment are presented in table 4. 



After 3 weeks of growth the plants were photographed (pi. 2) and 

 harvested. Data giving average stem height, green weight of tops, and 

 dry weight of tops and roots are given in table 5. 



Both the illustrations and plant data show that this group of plants 

 was normal in appearance and comparable to good greenhouse plants. 

 It was by far the best we have grown under the 100 percent artificial 

 conditions of our laboratory. In an earlier publication, Johnston 

 (1932) reported that tomato plants exposed to an intense illumination 

 from a Mazda lamp grew very well but soon became yellow in color. 



