NO. 2 PLANT GROWTH AND WAVE-LENGTH BALANCE JOHNSTON 5 



and then harvested. The average stem height and total dry weight 

 per plant for each of the three light conditions appear in the same table. 



Although the stems of plants in group 1-2 were thicker than those 

 in the other groups, their leaves were quite yellow. Here again yel- 

 lowing is associated with energy distribution where the greatest 

 amount is found in the red end of the spectrum. The plants in group 

 5-6 had the best color, even though the total amount of energy was 

 about half that of group 1-2. These leaves had flat smooth surfaces, 

 while those in group 1-2 were quite pointed and curled. The general 

 appearance of these plants is shown in plate i. After another experi- 

 ment with these lamps it was definitely indicated that the plants were 

 getting insufficient illumination. 



Experiment 5. — To increase the radiation, a General Electric 400- 

 watt high-pressure mercury lamp was substituted for the mercury 



Table 3. — Radiation intensities and average plant data from experiment 4 



Radiation intensity Average data 



at beginning of experiment per plant 



watts/cm^ 



\ Stem Total 



Culture Neon Mercury ht. dry wt. 



no. (red) (blue) Total cm gram 



1 00023 .00002 .00025 6.6 .029 



2 00019 .00002 .00021 6.6 .029 



3 00008 .00002 .00010 3.6 .014 



4 00008 .00002 .00010 3.6 .014 



5 00005 .00007 .00012 3.4 .013 



6 00005 .00007 .00012 3.4 .013 



grid and four instead of two transformers were used with the neon 

 lamp. The daily light period was increased from 12 hours to 18 

 hours. Because of the marked decrease in the life of the neon lamp 

 under these forced conditions, the experiment was discontinued at 

 the end of 20 days. In this exploratory experiment no accurate in- 

 tensity measurements were made. However, general improvement in 

 growth was noted. 



Experhnent 6. — To increase further the light intensity, a 1,000- 

 watt, iio-volt projection lamp housed in a water jacket as noted 

 earlier (experiment i) was substituted for the neon grid lamp. Three 

 plants per quart culture jar were used and the cultures run in dupli- 

 cate so far as the light relations were concerned. Throughout all 

 the previous experiments the plants were grown in a three-salt 

 nutrient solution similar to that used by Johnston and Dore (1929). 

 In this experiment cultures 2, 4, and 6 had (NH4)2S04 added to the 

 former solution which contained Ca(N03)2, MgSOi, and KH2PO4 



