NO. 3 RESPONSK O].' ALGAE TO ULTRAVIOLET MEIER 3 



erythema and subsequent browning induced by ultraviolet in the 

 human skin. Generally there is a latent period from 3 to 24 hours' 

 duration before erythema makes itself evident. Martin and West- 

 brook define as the latent period the time elai)sing between the irra- 

 diation and the visible culmination in browning. The term " latent 

 period " is in a sense comparable with its application to the appear- 

 ance during development of the latent image on a ]ihotographic plate. 



EXPERIMENTAL PROCEDURE 



The technique, methods, and apparatus used in this work are similar 

 to those described for the exposure of the second plate of Chlorella 

 vulgaris by Meier (1932) and by Brackett and McAlister (1932). 



In August 1932 three separate portions of each of 10 plates cov- 

 ered with Detmer .l-agar 1.5 percent al)out 4 to 5 mm thick, the entire 

 surfaces of which were uniformly green with cells of Chlorella 

 vulgaris, were irradiated in the quartz spectrograph using a quartz 

 mercury lamp as the source. Data regarding their inoculation and 

 irradiation dates together with the exposure times are listed in 

 table I. In April 1933 nine additional plates (plates 14 to 17 and 

 19 to 23) that had been prepared in a similar fashion were also 

 irradiated as n(jted in table 2. The intensity data are given in table 3. 



EFFECT OF ULTRAVIOLET RAYS ON AGAR PLATES 



Two blank agar plates (plates 18 and 24) that had been made at the 

 same time as plates 14 to 17 and 19 to 2t^ and left under similar 

 conditions but not inoculated with algae were also irradiated in April 

 1933. Separate portions of plate 18 were irradiated for 64, 16, and 

 32 minutes, and separate portions of plate 24 were irradiated for 16, 

 4, and 8 minutes. When the plates were finally examined 2 months 

 after inoculation, there was no evidence of any differentiated regions. 



On June 24 a freshly inoculated Detmer ^ solution of Chlorella 

 vulgaris was poured over plate 18, and after a short interval the 

 excess was removed. The plate was then placed in a north window. 

 Within 3 weeks' time the plate was covered with a uniform green 

 growth of the algal cells. 



This experiment seems to indicate that the wave lengths which 

 prove lethal to the green cells of the algae do not affect the culture 

 medium which covers the glass plate in any way that will accelerate 

 or retard the subsequent growth of the algae. 



