RADIUM RAYS 



229 



Fig. 8. 



tarded by the rays from the mantle, and Fig. 9 shows the appearance 

 of the culture seven days after the experiment was started. 



The influence of radium rays on photosynthesis was tested in sev- 

 eral ways. For example: A nasturtium {Tropceolum) plant was 

 placed in sunlight after having been in darkness for 18 hours. Under 

 one of the leaves, and lightly in contact with it, was placed a Lieber's 

 coated rod of undetermined (probably 25,000) activity. After twenty- 

 four hours the leaf was dechlorophyllized and stained with iodine to 

 test the presence of starch. Starch was almost entirely wanting in the 

 part of the leaf that was directly over the radium-coated rod, but was 



Pig. 9. 



