6 SMITHSONIAN' MISCELLANEOUS COLLECTIONS VOL. 98 



minutes. After being thoroughly agitated, ioo cc. of the culture were 

 poured into a second 300-cc. Erlenmeyer flask so that duplicate cul- 

 tures were obtained for each exposure. The flasks were equipped with 

 rubber stoppers, which were found to be more satisfactory than cotton 

 plugs, previous experimentation having shown that the algae grew 

 equally well in the rubber-stoppered flask and the flask with a cotton 





Fig. 1. — Quartz tube with flattened side and stirrer. Natural size. 



plug provided the cultures were inoculated a week or more after the 

 flasks of culture medium had been autoclaved. 



The cells of three drops of the culture from each flask were counted 

 directly after irradiation, and the mean of the three cell counts was 

 taken as the initial cell count. The same pipette used for making the 

 drops for the initial count was marked, cleaned with ether, and put 

 awav for use with the same culture 2 weeks later when the final count 



