NO. 23 STIMULATION OF ALGAE BY ULTRAVIOLET— MEIER 5 



The unicellular green alga Stichococcus bacillaris Naegeli lends 

 itself more satisfactorily to precise and accurate counting and measure- 

 ment because of its size and method of multiplication. This alga has 

 an elongated cell usually varying from 2 to 2.5 11 in width and 4 

 to 8 fx in length. Multiplication takes place by transverse division of 

 the protoplast that partially fills the cell and by the formation of cross 

 walls, thus developing two cells in place of the one parent cell. The 

 nucleus usually lies near the center of the cell. (See pi. 3.) Filaments 

 of more than two cells were rarely observed in my cultures. The alga 

 develops rapidly, forming a green deposit in Detmer 1/3 solution. 



The nutritive solution Detmer 1/3, which was used entirely for this 

 series of experiments, was made up in the following proportions and 

 then diluted 1/3 : 



Calcium nitrate 1 .0 gram 



Potassium chloride 0.25 



Magnesium sulphate 0.25 



Potassium acid phosphate 0.25 



Ferric chloride 0.002 



Distilled water 1.0 liter 



Before irradiation, algae were pipetted from actively growing cul- 

 tures into small quartz tubes, which were designed and constructed by 

 L. B. Clark, of the Division of Radiation and Organisms. One side 

 of each tube was flattened so as to insure equal and complete irradia- 

 tion of the contents. Each quartz tube was equipped with a slender 

 wire stirrer inserted through the cork so that the culture could be 

 stirred during irradiation. (See fig. I.) After the stemlike base of 

 the tube had been securely inserted in a rubber stopper so placed as 

 to hold the tube directly in the monochromatic ray of ultraviolet, the 

 tube was examined with a piece of uranium glass to insure that the 

 contents were covered by the ultraviolet ray. The quartz tube trans- 

 mitted approximately 90 percent of the ultraviolet ray. A separate 

 quartz tube was used for each exposure. Thermocouple measurements 

 of the intensity were made before and after each experiment. The 

 ultraviolet lamp was turned on half an hour before each experiment 

 so that the intensity of the radiation was constant when the thermo- 

 couple measurements were made. The control cultures were treated 

 exactly in the same manner as the irradiated cultures except that they 

 were not exposed to the ultraviolet. 



After irradiation, the contents of each tube were pipetted into a 

 300-cc. Erlenmeyer flask containing 200 cc. of Detmer 1/3, which 

 had been sterilized in the autoclave at 20 pounds pressure for 15 



