RADIATION AND ANTHOCYANIN PIGMENTS 1115 



upon water exposed to the lamp, colored at about the same rate as when 

 left intact. When the peel was heated or placed in alcohol or otherwise 

 treated so as to kill or injure the cells, no color developed. It was 

 believed that fruit did not color after a period in storage because of the 

 death of the cells in the epidermal layers, since most of these cells which 

 normally produce pigment were found dead when examined on November 

 8, after a period in cold storage. Both plasmolysis and reaction to vital 

 stains were used to determine vitality. The extreme ultra-violet region 

 beyond the limit for sunlight has been shown to be lethal to the cells of 

 plant leaves by Arthur and Newell (2) and by many other workers. 

 The intensity of this action increases rapidly with decreasing wave-length. 

 The failure of this extreme region to induce pigment formation is no 

 doubt due to the injurious effect upon the cells. 



It should be noted that the pigment formed in the apple is extremely 

 localized and restricted to only those cells which are exposed to light. 

 When a piece of clear cellophane is shellacked at the edges and stuck to a 

 green apple placed under the lamp, any mark drawn upon the cellophane 

 with India ink will protect those cells under the mark from pigment 

 formation. These cells so protected will remain green while the red 

 color develops over the remaining unprotected surface exposed to the 

 lamp. This principle has been used as a method of trade-marking or 

 labeling apples, Aubin (4) has also employed it in printing photographic 

 negatives on apples, using sunlight as a source. A preliminary study by 

 Arthur seems to indicate that not all red pigments produced in fruits 

 remain localized in the cells which produce them. Green cranberry and 

 Abundance plum fruits were found to produce pigment under the same 

 conditions as the apple when exposed to the mercury- vapor arc. When 

 narrow strips of gummed paper labels are pasted on such fruit during 

 the exposure, the cells mider the paper slowly take on a faint pink color 

 as the cells around the label, which are not protected, redden to the 

 normal color. It may be considered in this case that there was a diffusion 

 of pigment from the cells in which it was formed into neighboring (non- 

 illuminated) cells where no pigment would otherwise form. This 

 apparent migration, as has been pointed out, did not occur in the apple. 

 Red pigment also formed in darkness in both the cranberry and Abun- 

 dance plum but at a much slower rate than under the lamp. This was 

 not true of the apple. There is also the possibility that the pigment 

 itself does not migrate but rather that a reaction, which normally pro- 

 ceeds at a slow rate in darkness, is accelerated indirectly by the action 

 of light on the neighboring cells. Blinks (6) has shown that a migration 

 of pigment takes place within the cell during the flow of an electric current 

 through plant tissue. In one group of plants the pigment migrated 

 toward the positive or anode pole of the cell. The direction he found 

 could be reversed by immersing the tissue in acid solutions. In another 



