M 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 98 



STIMULATED GROWTH FROM OLD STIMULATED CULTURES 



In 1939 it was observed that the old cultures that had been growing 

 undisturbed since their growth count 2 weeks after irradiation in 

 1937 presented a sufficient growth of algae for weighing. Several 

 cultures were filtered, and when the dry weights were obtained the 

 weights of the stimulated cultures proved to be much greater than 

 those of the controls (see table 5). The 2652 A. cultures were filtered 

 through previously weighed filter paper, and then the precipitate 

 and the filter paper were dried in the electric oven before weighing. 

 The 2967 A. cultures were filtered through filter papers that had been 

 previously dried and each weighed with its small covered aluminum 

 pan. The filter papers of algae were then placed each in its pan in the 



Wave 

 length 



.4. 

 2652 



2967 



Table 5. — Dry Weight of Algae 2 Years after Inoculation 



Date 



1937 

 Mar. 30 



July 19 



Exposure 



Tare 



Tare + 

 Algae 



o sec. (control) 

 40 sec 



gm. 

 .624 

 •570 



o sec. (control) (A) . 17-993 



200 sec. (A) j 18.187 



o sec. (control) (B) . 17.674 



200 sec. (B) 17 .663 



gm. 



.647 

 .621 



17.998 

 18.208 

 17.681 

 17.681 



Algae 



gm. 



.023 I 



.051 2.2 



.005 I 



.021 4.2 



.007 I 



.018 2.6 



oven and dried for a much longer period than the 2652 A. cultures. 

 These data are of value in that they indicate continued increase in 

 multiplication of the cells for a period of 2 years. 



To check this finding, a series of experiments was performed with 

 cultures that had been irradiated and allowed to stand undisturbed 

 over a period of time. Flasks of fresh culture solution were inoculated 

 with inoculum from the stimulated cultures and from the control 

 culture of each series. Cell counts were made as described above 

 directly after inoculation, and 2 weeks after the new series of cultures 

 had been placed in the growth chamber. In each case, as shown in 

 tables 6-9, the growth rate was higher in the stimulated cultures than 

 in the control, proving that the accelerated rate of multiplication of 

 the algal cells, increased by irradiation with the ultraviolet, had per- 

 sisted for a period of 2 vears. 



