NO. 2 PLANT GROWTH AND WAVE-LENGTH BALANCE JOHNSTON II 



in which the greatest dry weight was produced per watt/cm° were the 

 same three cultures which received the greatest percentage of radia- 

 tion from the mercury lamp. In experiment 8, however, an exception 

 occurred. The dry weight efficiencies for the three groups of cultures 

 1-2, 3-4, 5-6, were 23.8, 28.6, 10.7 respectively, while the percentages 

 of total radiation attributed to the mercury lamp were 40, 25, and 7 

 for these same cultures in the order given. It is not clear from the 

 data at hand why this exception occurred. 



In order to compare all these data which are fairly comparable, 

 table 12 has been constructed. Since two types of solutions were used 

 in experiment 6, cultures 2, 4, and 6 were selected as their solutions 



Table 12. — Average dry weight production per unit total radiation (Mazda plus 

 mercury lamp) in relation to percentage of radiation from the mercury lamp 



Percentage 

 Experiment Culture Dry wt. per radiation from 



number number watt/cm^ mercury lamp 



7 6 37.4 45 



8 3 32.7 25 



6 6 32.4 51 



8 I 28.2 40 



7 I 27.6 29 



6 4 26.8 IS 



7 5 25.2 14 



8 4 24.4 24 



7 4 21.0 5 



6 2 20.3 3 



8 2 19.4 40 



7 3 17-8 5 



7 2 13.7 7 



8 6 ii.o 6 



8 5 10.3 7 



were similar to those used in experiments 7 and 8. All plant values 

 given in this table are the averages of three plants. There is a slight 

 difference in the duration of the three experiments which should be 

 kept in mind in making this comparison. In these experiments, 6, 7, 

 and 8, the plants were grown for 20, 18, and 21 days respectively. 



The data showing dry weight produced per unit total energy in 

 table 12 have been arranged from greatest to least value. The cor- 

 responding values showing the percentages of total radiation that are 

 obtained from the mercury lamp fall roughly into two groups. The 

 first eight values are high (14 to 51 percent). The remaining seven 

 with the exception of culture 2 in experiment 8 are low (3 to 7 

 percent). Although there is no regular decrease in these percentage 

 values with the decrease in dry weight per unit total radiation, there 



