NO. 10 ULTRA-VIOLET LIGHT ON GREEN ALGA MEIER 3 



matic light on paramoecia. Hutchinson and Newton (1930) have con- 

 tributed quantitative data on the effect of irradiation on yeast. Bucholtz 

 (1931) found that the cells of higher plants are more resistant to the 

 lethal action of ultra-violet light than bacteria and paramoecia. Wein- 

 stein (1930), Bucholtz (1931), and many of the other authors 

 have made comprehensive reviews of the literature on ultra-violet 

 irradiation. 



Of the recent investigators, Gates (1929. 1930) has most clearly 

 'demonstrated the value of the use of monochromatic light of different 

 intensities in the study of the lethal eft'ect of 10 lines of the mercury- 

 vapor spectrum on bacteria. By the use of a specially constructed 

 monochromator and a thermopile he found the wave-length limits of 

 the bactericidal action to be between 3,130 and 2,250 A., although the 

 lower limit could not be positively ascertained. 



EXPERIMENTAL PROCEDURE 



Chlorella vulgaris, the alga which was used in this experiment, is a 

 unicellular green alga, the spherical cell containing a parietal chromato- 

 phore and one easily visible pyrenoid. The diameter of the cell is 

 usually 3-5/x, although some giant cells exceed iO;ti,. It multiplies by 

 oval or elliptical spores, usually two to four in number. This alga has 

 been maintained in pure culture in my collection for two years. 



The nutritive solution in which the algae were grown is Detmer 1/3, 

 a modified Knop solution, made up in the following proportions and 

 then diluted to one-third : 



Calcium nitrate . . . : i- gram 



Potassium chloride 0-25 



Magnesium sulfate 0.25 



Potassium acid phosphate 0.25 



Distilled water i- liter 



Ferric chloride ^ trace 



Petri dishes 9.5 mm in diameter containing the above solution plus 

 2 per cent agar were sterilized in the autoclave at 15 pounds pressure 

 for 20 minutes. When the media, which was about 4 mm thick, had 

 solidified, a suspension of green cells of Chlorella vulgaris that had 

 been growing in Detmer 1/3 solution in diffuse light was poured over 

 the agar in the petri dish. This suspension of green cells was allowed 

 to remain on the media for 24 hours, then the excess was poured off. 

 The covered culture was placed under a bell jar and grown in diffuse 

 light from a north window during the month of July. After a 



