1112 BIOLOGICAL EFFECTS OF RADIATION 



autumnal reddening of leaves. From the foregoing literature the only- 

 change in the carbohydrate and nitrogen fractions of leaves which redden 

 during autumn which has been consistently observed by the various 

 workers is loss of nitrogen. It might be concluded, therefore, that loss 

 of nitrogen from lea^^es is a cause of pigment formation, but when the 

 variations in the different fractions with species just mentioned are 

 considered, it seems as logical to conclude that further careful analytical 

 work may reveal some exceptions even in the case of loss of nitrogen. 



RELATION OF ANTHOCYANIN PRODUCTION TO ENVIRONMENT 



In a multiconditioned natural environment it is always diflficult to 

 determine which factor or factors affect a given process in plants. This is 

 true of pigment formation. In order to determine more accurately the 

 part which each factor plays in the development of pigment much progress 

 might be made by growing many species of plants which form pigment 

 in an artificial climate where various climatic factors were carefully 

 controlled. So far this has not been done. In the absence of such a 

 study some information may be gained by a consideration of work with 

 various separate plant organs such as leaves, fruits, stems, and bulb 

 scales held under more accurately controlled conditions. 



Mirande (21) observed that the bulb scales of lilies produced a red 

 pigment when removed and exposed to diffuse daylight or to artificial 

 light. The scales were exposed under one to six layers of white silk 

 transmitting from 0.53 to 0.07 of the intensity of sunlight as measured 

 by a photometer. At an altitude of 300 meters the reddening did not 

 take place in open sunlight or under one layer of cloth, but started under 

 two layers and reached a maximum under three layers. At 600 meters 

 the reddening began under three layers and reached a maximum under 

 four layers. At 2000 meters the reddening started under three and 

 four layers and reached a maximum under six layers. In diffuse light 

 pigment is developed under glass-water filters and also under a solution 

 of alum in glass used as a filter, showing that the extreme ultra-violet 

 and infra-red regions are not required. Pigment is not developed under 

 these filters in open sunlight. The author concludes, therefore, that the 

 active rays are in the visible region. By means of various filters (liquid, 

 colored glass, and Wratten) Mirande found that the blue-violet region 

 was most effective in producing color and the red was second in impor- 

 tance, while the green produced no color. It is evident from the fore- 

 going that even a reduced intensity of light in the blue-violet region is 

 effective in producing red pigment on the bulb scales of lily. Since 

 temperatures were not controlled in these tests, there is the possibility 

 that higher temperatures inhibited pigment formation in the open sun- 

 light as well as high light intensity, while both lower temperatures and 

 higher light intensities which usually obtain in the higher altitudes might 



