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COLONIAL FORMATION OF UNICELLULAR GREEN 

 ALGAE UNDER VARIOUS LIGHT CONDITIONS ^ 



By FLORENCE E. MEIER 



Division of Radiation and Organisms, Smithsonian Institution 



(With Three Plates) 



INTRODUCTION 



Light of certain ranges of wave lengths and intensity is generallv 

 considered essential for the formation of chlorophyll in green plants. 

 A number of green algae, mosses, and pine seedlings prove to be 

 exceptions to this generalization. For example, Sccncdesmxis oh- 

 fusiusculus Chodat and Scenedcsntus chlorelloides Chodat develop and 

 maintain their green chlorophyll better in darkness than in light. 

 Different green algae, however, vary in their reactions to light con- 

 ditions just as different higher plants vary in their reactions to 

 temperature and other environmental conditions. Chlorclla nibescens 

 Chodat forms chlorophyll in the dark but not so vigorously as in 

 the light, while the cells of Sccnedesmiis qitadricauda are dark green 

 in dift'use light and pale green in direct light. 



The ability of these plants to form chlorophyll without the aid of 

 natural or artificial light is generally attributed to the presence of 

 assimilable carbohydrates in the nutrient solution in which they are 

 growing. Chodat (T913) has shown in the case of Stichococcns bacil- 

 laris that when a carbohydrate is assimilated with difficulty or not 

 assimilated at all by an alga in the dark as demonstrated by its de- 

 coloration or complete lack of growth, the growth and development 

 of chlorophyll by the same alga in the light is not prevented in the 

 slightest degree. Chodat carried on a long series of experiments to 

 determine the type of sugar best assimilated by certain algae growing 

 in darkness. For that reason, further discussion of the necessary 

 nutriments will not be treated here. 



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 1931 to 1933. 



Smithsonian Miscellaneous Collections, Vol. 92, No. 5 



