Brtbur jfun& 



EFFECTS OF INTENSITIES AND WAVE LENGTHS OF 

 LIGHT ON UNICELLULAR GREEN ALGAE ^ 



By FLORENCE E. MEIER 



Division of Radiation and Organisms, Smithsonian Institution 



(With Three Plates) 

 INTRODUCTION 



Unicellular green algae are admirably adapted to the study of the 

 effectiveness of light intensity and light of different wave lengths on 

 chlorophyll formation and on growth as defined by multiplication of 

 cells. Their chief advantages as subjects of experimentation are : 

 (i) their small size, the mechanism of photosynthesis being complete 

 in the microscopic individual with its green chloroplast ; (2) the uni- 

 formity of their surfaces, since each cell in those varieties that do not 

 form zoospores may be considered comparable to every other one 

 placed in a symmetrical environment; (3) their mode of growth in 

 nutrient solution ; and (4) the comparative ease of controlling the 

 temperature and humidity conditions. 



Control of the environment of algae as regards culture medium, 

 temperature, and illumination was made the primary consideration in 

 these experiments conducted in an effort to determine the reaction of 

 algae to light. The importance of controlled conditions especially in 

 matters of light intensity and wave length is easily seen when one 

 reads through the literature. A few results of other investigators are 

 reviewed. 



I wish to express my deep appreciation to Dr. C. G. Abbot, Secre- 

 tary of the Smithsonian Institution, and to Dr. Earl S. Johnston, 

 Assistant Director of the Division of Radiation and Organisms, for 

 their assistance in the completion of this piece of research. I am 

 also very grateful to the other members of the Division of Radiation 

 and Organisms, whose united efforts have made possible these 

 experiments. 



1 This paper reports investigations made under a grant from the National 

 Research Council to the author as National Research Fellow in the Biological 

 Sciences from July 193 1 to July 1933. 



Smithsonian Miscellaneous Collections, Vol. 92, No. 6 



