220 ASCORBIC ACID 



in the cell with the reduction of nitrate is not new. It has recently been 

 shown that seedlings given nitrate may be unable to grow after removal of 

 cotyledons or endosperm unless ascorbic acid, glutathione, or other reduc- 

 ing substances are added, whereas excised seedlings given nitrogen in the 

 form of ammonium salts continue normal development in the absence of 

 any supplements.^^ 



d. Light 



Light has a beneficial effect upon the production of ascorbic acid in 

 plants. ^^ The concentration of ascorbic acid in plant leaves fluctuates con- 

 siderably during the day, the maximum being reached in the forenoon.^* A 

 fall in the ascorbic acid content of plants has been observed when they 

 were transferred from light to dark, and also when parts of the plant were 

 shaded. ^^ With fruits the concentration of ascorbic acid varies with the 

 degree to which the fruit is exposed to svmlight.^® A direct relationship be- 

 tween the ascorbic acid formed and the light intensity has also been ob- 

 served with turnip leaves." The effect of light varies with the wavelength; 

 red light is the most effective both for the production of ascorbic acid and 

 for photosynthesis,'^^ whereas the rays of the blue-violet end of the spec- 

 trum have no influence. ^^ Certain experimental results support the view 

 that the synthesis of ascorbic acid is linked with photosynthesis. Seedlings 

 deprived of their reserves and grown in light without carbon dioxide (no 

 photosynthesis) show a fall in the concentration of ascorbic acid in their 

 tissues. ^'^ Rhizomes of Stachys which had developed chlorophyll under the 

 influence of light contained more ascorbic acid than controls kept in the 

 dark.^i With cut discs of turnip leaves the ascorbic acid increased in the 



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66 N. V. Veselkine, V. N. Lubimenko, Z. P. Boulgakova, V. V. Tikalsskaia, and P. S. 

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