2 SMITHSONIAN MISCELLANEOUS COLLECTIONS \ OL. 92 



The micro-moving-picturcs and niicrophotographs made by Franklin, 

 Allen, and McDonald (1933) show how ultraviolet irradiation below 

 2900 A causes immediate cessation of all motion of the unicellular 

 organisms followed by marked internal changes and in some cases a 

 complete breakdown of the cellular structure. Swann and del Rosario 

 (1932) noted that the death rate of the cells was not related to the 

 intensity of the light nor to the number of the cells present, but to 

 the length of exposure. Furthermore, cells continued to die even after 

 the light was removed. In the work here reported it was similarly 

 observed with algae that certain ultraviolet rays injured the cells but 

 that death followed some time later. Swann and del Rosario found 

 that the total number of Eugleiia cells that died subsequently as the 

 result of irradiation was proportional to the total quantity of radiant 

 energy in question, within the limits of intensity and concentration 

 investigated. 



The algal cells did not begin to die as soon after irradiation as 

 did the Englcua cells. This may be due to a difference in the irradia- 

 tion intensity. Tanner and Ryder (1923) found in their irradiation 

 experiments that pigmented yeasts are more resistant than white 

 yeasts and also that yeasts live a little longer than bacteria, a fact 

 that they explain as due to the difference in size. 



The work of Beauverie and Cornet (1929) on the leaf and bud 

 of lilodca canadensis shows that the chloroplastids in the cell with- 

 stood continued irradiation much better than did the cytoplasm, 

 mitochondries, and chondriocontes. 



Noethling and Rochlin (1931) also irradiated Elodca with ultra- 

 violet rays less than 3000 A in wave length and found a cessation 

 of plasma streaming, also the appearance of oxalate crystals, and 

 necrosis. 



Gibbs (1926) noted that a latent period occurred before death in 

 irradiated filaments of Spirogyra iiitida aifiuis. The limits of the toxic 

 action were the wave lengths 3126 and 2378 A. The chloroplasts were 

 observed to clump characteristically, owing to the great difference in 

 intensity of radiation reaching the " near '' and " far " sides of the 

 filament. The behavior of the filaments was variable. Some died 

 while apparently perfectly normal in appearance. Coagulation of the 

 protoplasm was noted, also a brown precipitate that exhibited Brown- 

 ian movement. 



Martin and Westbrook ( 1930) .reported browning of the cells of 

 the leaves of Voandacia, Pelargoniitiii, and other plants by ultra- 

 violet irradiation. The browning was compared to the reddening or 



