﻿24 BOTANICAL GAZETTE [januaey 



macrosporoidium). The Schumann rays have not sufficient pene- 

 trating power to pass through the colored cell walls. 



By this method we were comparing the time required to kill 

 spores in air with the time required to kill them in a vacuum, but 

 preliminary experiments in which the hemisphere K was brought 

 very close to the fluorite window D showed that the presence or 

 absence of air makes no difference in the length of exposure required 

 for killing. It should be pointed out that for these experiments 

 organisms were selected which had very thin and transparent cell 

 walls. It was impossible to obtain similar results with organisms 

 with thick, dark-colored spore walls. The length of exposure 

 required to kill dark-colored spores was so great that it is doubtful 

 if the Schumann rays took any part in the killing. 



The light emitted from the fluorite window of the hydrogen dis- 

 charge tube is much less destructive when the light waves of a 

 length shorter than 1700 Angstrom units are filtered out. The 

 results obtained by the three methods are comparable. The light 

 is 15-20 times more destructive when it contains the short waves 

 than when it does not. The significance of these figures lies in the 

 fact that in the Schumann region, as in the regions of longer wave 

 length, the destructive action of the light increases as the wave 

 length decreases. Necessarily, this statement does not hold true 

 for organisms protected by membranes which are opaque to the 

 Schumann rays. 



Summary 



By a number of methods it has been shown that the action of the 

 light is on the organism directly, and not indirectly through the 

 formation of some toxic substance in the medium. 



It is a well-established fact that the Schumann region of the 

 spectrum is a region in which nearly all substances have strong 

 absorption bands. While no studies have been made upon the 

 absorption of protoplasm in this region of the spectrum, un- 

 doubtedly strong absorption does occur. Gelatin, which is a much 

 simpler substance than protoplasm, is so opaque to the rays that 

 the ordinary photographic plate cannot be used in photographing 

 the Schumann spectrum. Special plates, in which the silver salts 



