2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 92 



RESULTS OF PREVIOUS INVESTIGATIONS 



As early as 1861 Sachs (1864) originated the well-known method 

 of growing plants in double-walled glass cylinders to determine the 

 effects of colored lights. The cylinders contained respectively solu- 

 tions of ammoniacal copper oxide for blue light, and potassium di- 

 chromate for orange light. No coloring solution was used with the 

 third cylinder. He reported that plants needed from 4 to 6 days more 

 in blue light than in orange light to unfold their leaflike cotyledons 

 which remained smaller in the former so that the lamina in orange 

 light was 2 to 3 times larger than in blue light, but largest of all in 

 white light. Regarding leaf formation, the orange light acted as a 

 lesser, the blue as a higher, degree of darkness. There was no for- 

 mation of organic substance in the blue light, while a small amount 

 was 'formed in orange light. 



Pfeffer (1871) also working with double-walled cylinders of solu- 

 tions found the following percentages of growth under the filters: 

 46.1 percent, yellow; 32.1 percent, red and orange; 15.0 percent, 

 green; and 7.6 percent, bkie, violet, and indigo. Later, in 1872, work- 

 ing with a prism he again found the maximum growth in the yellow. 



Weber (1875) working with colored glasses as filters obtained 

 similar results but in the following different percentages : 82.6 per- 

 cent, yellow; 35.5 percent, red; 22.4 percent, blue; and 14.5 percent, 

 violet. 



Wiesner (1877) used a filter of potassium dichromate which trans- 

 mitted the less refrangible half of the spectrum: red, orange, yellow, 

 and a part of green ; and also ammoniacal copper oxide which allows 

 the passage of the remainder of the visible rays, the rest of the green 

 and all of the blue and violet. He observed that the plants in weak 

 light became greener sooner under yellow but in strong light sooner 

 under blue. He believed rapid destruction accompanies chlorophyll 

 formation in strong yellow or strong blue light which might not act 

 directly upon the chlorophyll already formed but might have a harm- 

 ful effect upon some process antecedent to chlorophyll formation. 



Zachariewicz (1895), Flammarion (1897), and Strohmer and Stift 

 (1905) agree that the maximum chlorophyll production is in the 

 yellow rays. 



Artari (1899) observed that blue-violet light accelerated the de- 

 velopment of Chlamydomonos chrcuhcrgii. 



Teodoresco (1899) using filters made up of chemical solutions 

 studied the growth of corn in regions of the spectrum corresponding 

 to the general chloroiihyll absorj-jtion bands. Growth was found to be 



