STIMULATIVE EFFECT OF SHORT WAVE LENGTHS 



OF THE ULTRAVIOLET ON THE ALGA 



STICHOCOCCUS BACILLARIS 



By FLORENCE E. MEIER 

 Division of Radiation and Organisms, Smithsonian Institution 



(With Four Plates) 



INTRODUCTION 



During the course of previous quantitative research on the lethal 

 effect of 21 wave lengths of the ultraviolet ranging from 2250 to 

 3130 A. on a green alga, the author (Meier, 1932, 1934, 1936) ob- 

 served from time to time accelerated increase in cell mass with slightly 

 less exposure than the lethal exposure that destroyed the plant cells. 

 The purpose of the present study is to show quantitatively the stimula- 

 tive action of definite short wave lengths of the ultraviolet on growth 

 as measured by cell multiplication in a unicellular green alga, a stimu- 

 lative action that has persisted over a period of 2 years in the same 

 cultures without additional treatment. 



By means of a quartz mercury-vapor arc and a fused-quartz prism 

 spectrograph, exposures were made to the wave lengths 2652 and 

 2967 A. A spectrograph with crystal quartz prisms was used for the 

 irradiations with the wave lengths 2352 and 2483 A. Absolute mea- 

 surements of the intensity of the lines were made with a Clark vacuum 

 thermocouple as described by Johnston and Weintraub (1939) and a 

 double monochromator as in the method described by Brackett and 

 McAlister (1932). 



The spectroscopic manipulations and physical measurements were 

 made by Dr. E. D. McAlister, of the Division of Radiation and 

 Organisms. 



I wish to express my appreciation to Dr. C. G. Abbot, Secretary 

 of the Smithsonian Institution, for his counsel and assistance during 

 the progress of this investigation. I am also grateful to Dr. E. S. 

 [ohnston and other members of the Division of Radiation and Or- 

 ganisms who have aided me in this research. 



Smithsonian Miscellaneous Collections, Vol. 98, No. 23 



