2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 92 



The experiment described below is one carried out preliminary to 

 an elaborate piece of research under definitely controlled conditions 

 on the effect of light intensity and wave length on algae. A number 

 of different algae from my collection in pure culture were studied to 

 determine their general reaction to natural and artificial light and to 

 total absence of light. 



I wish to express my appreciation to Dr. Earl S. Johnston, As- 

 sistant Director of the Division of Radiation and Organisms, Smith- 

 sonian Institution, for his aid and suggestions. I am also very grateful 

 to Dr. W. T. Swingle, of the United States Department of Agricul- 

 ture, for his cooperation in obtaining the excellent color plates of 

 the algal cultures made by Marcel L. F. Foubert, of the Photographic 

 Division of the Department of Agriculture. 



DISCUSSION OF LITERATURE 



Numerous w^orkers have studied the effect of varying day lengths 

 on higher plants. The recent work by Arthur (1930), Garner and 

 Allard (1925), and Shirley (1929) covers the field very well, and 

 their long lists of literature references are an indication of the work 

 done on this subject from the time of Herve Mangon (1861), who 

 found that grain planted in darkness turned yellow while that in 

 electric light was green and thriving, up to the present when the 

 beneficial amount of artificial light that should supplement winter 

 daylight has been ascertained for various plants. References to the 

 effect of light and darkness on lower plants are not as abundant. 



Klebs (1896) studied the effect of light and darkness on gamete 

 formation in Clilamydoiiwnas media Klebs and demonstrated that 

 only vegetative division takes place in darkness. A 2 percent sugar 

 solution aided growth but did not entirely replace the light. 



Etard and Bouilhac (1898) recorded the presence of chlorophyll 

 in a Nostoc cultivated in the dark in a nutrient solution to which 

 glucose had been added. They extracted the chlorophyll with alcohol 

 and found the resulting yellow-green solution showed a red fluores- 

 cence and had the following absorption bands : 6900 to 6500 A, 6310 

 to 6060 A, 5890 to 5680 A, and 5480 to 5360 A. 



Artari (1899, 1900, 1902) studied Pleurococcus and Sccnedesmus 

 in media containing peptone, glucose, maltose, beet sugar, or mannite 

 and found growth in conjunction with chlorophyll formation taking 

 place not only in the light without carbon dioxide but also in absolute 

 darkness. He also reported chlorophyll formation in the dark for 



