252 Pennington — A Chemico-Physiological 



he finds to extend from 459 //// to 445 /*/*., with the centre 

 at 450 fifi. The violet screen, from 449 jifi to 417 /*/*, in- 

 cludes part of this band, which Mann says is not a well- 

 defined one, and also includes the absorption band which 

 we invariably find at the extreme end of the spectrum. 



Under the orange screen we have no absorption band ; 

 the yellow, likewise, is not absorbed, and under the green 

 screen a few, only, of the rays coincide with those which 

 are absorbed. But plants grown under these screens show 

 striking variations from one another and from the normal, 

 and the orange, where, according to the absorption theory, 

 growth should not occur, gave, next to red, a growth more 

 nearly approximating the normal than did any other. 



Such facts cannot be reconciled with either of the theories 

 above given, since it is apparently not so much the absorp- 

 tion of the rays, as the amount of energy which they pos- 

 sess which influences assimilation for either good or evil. 



According to Langley the greatest amount of energy, as 

 measured by the bolometer, is furnished by the orange rays. 

 Following this statement, growth should here be at its 

 maximum, but the foregoing experiments with Spirogyra 

 gave a more normal growth under red, in which the energy 

 is somewhat lower. 



The very peculiar behavior under the yellow screen I am 

 inclined to attribute to the action of these rays on the 

 hydrolysis of starch. This is converted into soluble carbo- 

 hydrate so rapidly that the nitrogenous products, which 

 normally are in sufficient quantity to combine with it to 

 form higher compounds, are in this case unable to do so. 

 The sugar, therefore, accumulates in the cell, upsetting the 

 perfect balance of power which should prevail. The in- 

 roads of the fungus cannot then be withstood, and the 

 plant dies. 



If we accept the red, as the region of greatest growth, or 

 the junction of red and orange, we must conclude that the 

 maximum hydrolytic activity is not conducive to the wel- 

 fare of the plant ; and we must also, from the experiments 



