NO. 2 PLANT GROWTH AND WAVE-LENGTH BALANCE JOHNSTON 9 



During the experiment water was added and fresh nutrient sokition 

 renewed as required. Because of frequent stopping of rotating table 

 no. I, these plants were slightly burned. These plants had the shortest 

 internodes. Plants in culture 6 had next to the shortest internodes 

 and were the best green. The leaves of plants in cultures 2, 3, 4, and 

 5 were slightly chlorotic. In order of their dry weights, plants in 

 cultures i, 6, and 5 were the best. It is interesting to compare the 

 total dry weight per unit total energy with the percentage of energy 

 received from the mercury lamp (table 9). 



Table 9. — Comparison of dry weight efficiency mith amount of radiation from 



the mercury lamp 



Cultures 12 3 4 S 6 



Ratio total dry wt. to watts/cm^ 27.6 13.7 17.8 21.0 25.2 37.4 



Percentage radiation from mercury lamp 29 7 5 5 14 45 



Plants in cultures 6, i, and 5 produced the greatest amount of dry 

 weight per watt/cml These same cultures in the order given received 

 the largest percentages of radiant energy rich in the blue. Total 

 energy (table 6) was greatest for culture i and least for culture 6. 

 Cultures 2, 3, and 4 were practically equal. Thus, plants of culture i 

 had the greatest total dry weight, and those of 6 were second. How- 

 ever, for greatest efficiency in the production of dry weight, plants 

 in culture 6 were much better than those in culture i. This is evi- 

 dently related to the greater percentage of shorter wave length in 

 the one case than in the other. When light intensity as measured 

 by the foot-candle meter is considered, plants of culture i are shown 

 as receiving the greatest amount of light and those of culture 2 the 

 next greatest amount. 



By consulting the table of stem heights it will be noted that the 

 average height at harvest for plants in culture i was less than any of 

 the other groups although the average original height was greatest. 

 The least average stem elongation shown by this group may be cor- 

 related with the greatest amount of total energy received by these 

 plants. . But little difference in stem height is seen between plants 

 of the other cultures. Likewise there is but little difference in total 

 energy received by these same cultures. Other observations bear out 

 this same point that an intense light retards stem elongation more 

 than a less intense one. Although the shorter wave lengths have a 

 greater retarding effect, this difference between plants of cultures 6 

 and I must have been offset by the differences in total radiation 

 intensities. 



