DIFFERENCE IN THE ACTION OF RADIUM ON GREEN 

 PLANTS IN THE PRESENCE AND ABSENCE OF LIGHT. 



By CHARLES PACKARD. 



{From the Marine Biological Laboratory, Woods Hole) 

 (Received for publication, July 18, 1918.) 



Experiments by Willcock^ on the effect of radium radiations on 

 Hydra viridis and Hydra fusca show that the green form is far more 

 resistant to rays than the brown. The green hydras are not killed 

 by an exposure of 4| hours to 50 mg. of radium bromide; the brown 

 hydras, on the other hand, die after "comparatively short exposures." 

 I have repeated this experiment several times and have obtained the 

 same results. Willcock also found that protozoa containing chloro- 

 phyll are uniformly more resistant than those which have none. 

 Since these experiments were carried on in daylight, it seemed pos- 

 sible that the difference in the reaction between the two classes 

 of animals experimented upon might be due to the activity of the 

 chlorophyll. 



If this assumption is correct, we should expect that plant cells 

 radiated in complete darkness, when the chlorophyll is not active, 

 would be more sensitive to the rays than in the light. To test this 

 point I have made a number of experiments on Spirogyra and Volvox. 



The radium (20.4 mg. of element, enclosed in a thin-walled silver 

 tube) was placed in a watch-glass filled with water, and the Spirogyra 

 filaments were laid across it. In the light, the cells nearest the tube 

 began to show a typical phenomenon of disintegration in 2 to 3 

 hours. This disintegration consists in the following. 



The chlorophyll bands first contract somewhat, losing their spiral 

 arrangement. A few minutes later they resolve into an irregular heap 

 of chlorophyll in one end of the cell. In the light, this phenomenon 

 began to be noticed after an exposure of from 2\ to 3 hours. The 



1 Willcock, E. G., /. Physiol., 1904, xxx, 449. 



37 



