ULTRA-VIOLET RADIATION 37 



assimilation in a high light intensity than do plants grown in 

 a weak light and vice versa. 



The balance of evidence favours the view that comple- 

 mentary chromatic adaptation is a natural phenomenon 

 although not so widely spread as has been supposed, and that 

 it is of little value to study the effect of light quality without 

 considering light intensity. 



To return to the main thesis : in all these observations the 

 significant fact is that the longer rays bring about a profound 

 chemical change, whereas in inorganic photochemistry the 

 short rays are by far the most efficient, the longer having little 

 or no action. For this reason not a little work has been done 

 on the action of the short rays, the ultra-violet, in bringing 

 about the formation of organic compounds from carbon 

 dioxide and water. All such work, interesting though it 

 be, throws no light on the fundamental problem of carbon 

 assimilation, since the green plant can effect the transformation 

 in conditions which preclude the presence of ultra-violet 

 illumination. With this caution a brief resume of such 

 investigations may be given. 



Stoklasa and Zdobnicky * brought about the synthesis 

 of carbohydrate in the absence of chlorophyll by passing light 

 from a quartz mercury lamp through a mica window into a 

 vessel containing a mixture of carbon dioxide and nascent 

 hydrogen. Formaldehyde was slowly produced, and this, in 

 the presence of caustic potash, was polymerized with the 

 formation of a sugar or a mixture of sugars which was optically 

 inactive and not fermentable by yeast. The authors suggested 

 that the chlorophyll in plants acts as a means of absorbing 

 ultra-violet rays, a suggestion which has since been found to 

 be true. Bertholet and Gaudechon f found that formalde- 

 hyde is produced by the action of ultra-violet rays on carbon 

 dioxide in the presence of a reducing agent, and, reversely, that 

 carbohydrates are decomposed by sunlight and by ultra-violet 



* Stoklasa and Zdobnicky : " Chem. Zeit.," 1910, 945. 

 f Bertholet and Gaudechon : " Compt. rend.," 1910, 150, 1690, 151, 

 395 ; 1912, 155, 401, 831. 



