1110 BIOLOGICAL EFFECTS OF RADIATION 



impressed by the curious fact that chlorophyll and the red pigments 

 formed by light were also decomposed again by the same agency. On 

 account of the immediate appearance of red and yellow pigments upon the 

 disappearance of chlorophyll in the fall he was led to believe that these 

 pigments were formed by the decomposition products of chlorophyll. 

 This confusion of ideas persisted until recently when the chemical identity 

 of chlorophyll and of the red and yellow pigments was established by 

 Willstatter (34) and others. More recently the chemical synthesis of 

 many of the anthocyanins has been accomplished. This work has been 

 critically discussed and summarized by Karrer and Helfenstein (16). 

 The apparent production of yellow pigments in autumn leaves, citrus 

 fruit, and elsewhere as chlorophyll disappears should not be confused 

 with the production of pigment by the direct action of light. Often the 

 yellow pigments, carotene and xanthophyll, already exist in such leaves 

 and fruit but are masked by the presence of chlorophyll. When the 

 chlorophyll is decomposed by light or other agency the yellow pigment 

 remains, and this results in a rapid change of color from green to orange 

 or yellow. In some roots, flowers, and fruits the carotinoid pigments 

 are developed in the complete absence of chlorophyll. The effect 

 of radiation on the development of the carotinoid pigments, as well as 

 its effect on chlorophyll development, is considered elsewhere in this 

 monograph. The present discussion is limited to the anthocyanins. 



LIGHT AND ANTHOCYANIN PIGMENTS 



Askenasy (3), Beulaygue (5), and Gertz (14) studied the development 

 of red pigments in several flowers and leaves kept in darkness and found 

 that these pigments were often greatly reduced or failed to develop 

 entirely in some species in darkness. Onslow (25) has listed various 

 organs of a number of plants which form anthocyanin in darkness and 

 has also given a similar list in which light appears necessary for the 

 formation of pigment. Gertz found that autumn-colored leaves of 

 various species of Viburnum, Cornus, and Prunus often showed natural 

 photographs of the leaves covering them. Anthocyanin pigments 

 developed only on those cells which were exposed to light. Linsbauer (19) 

 working with etiolated buckwheat seedlings {Fagopyrum esculentum) 

 found that the amount of pigment developed when exposed to a lamp 

 depended upon both the intensity and the time of exposure. 



CARBOHYDRATE ACCUMULATION AND ANTHOCYANIN DEVELOPMENT 



Onslow (25, page 90) pointed out that it is difficult to determine in the 

 experiments of Linsbauer whether the appearance of anthocyanin is 

 due to the direct action of light or to the products of photosynthesis 

 induced by light. This confusion of the factors producing anthocyanin 

 exists in both the older and later literature on the subject. Onslow 



