250 Pennington — A Chemico -Physiological 



the blue still more unfavorable to sugar production, while 

 the violet rays are only one-half as rapid as the red. 



In diffuse daylight the action of these rays is much less 

 marked, the ratio between yellow and white being as 1 : 0.92. 

 As diffuse yellow light exercises less influences for good 

 than does bright yellow light, so is the destructiveness of 

 the blue and violet lessened by diffuse light. 



In the experiments made by Green, the enzyme was ex- 

 posed first to the influence of light, then mixed with starch 

 paste and its activity noted. As the conditions in these 

 experiments were slightly different, starch and diastase 

 being mixed first, then exposed to light, it was deemed ad- 

 visable to expose diastase in solution to light, as did Green 

 then test its activity under the colored screens. Such tests 

 showed that the solution became rapidly weaker in light, 

 but in colored light maintained its relative strength. 



This behavior indicates a protective influence of starch 

 on diastase when exposed to light. It is even more than 

 that, since in the one case light accelerates, and in the 

 other retards its hydrolytic activity. 



Interpretation. 



The relation of light to plant growth being one of the 

 most interesting and wide-spread of all the many questions 

 with which the plant physiologist has to deal, it has nat- 

 urally received much attention. And while each portion 

 of the spectrum has been considered by the various workers, 

 the greatest amount of interest centres in the red-orange 

 and yellow, because of the theories which have been built 

 upon the study of the behavior of these rays in regard to 

 plant assimilation. It is the portion of the spectrum con- 

 taining the less refrangible rays which, from Sach's time 

 onward, has been recognized as best promoting plant growth. 

 According to Lommel, Miiller and Timiriazeff this is be- 

 cause the rays, absorbed by chlorophyll, have their energy 

 converted into some Other form of energy, which is then 

 capable of bringing about the decomposition of carbon 



