ULTRA-VIOLET AND SEED PLANTS 879 



daylight often gave a higher concentration of chlorophyll than any other 

 light qualities used under the same intensity. At the same time the 

 chlorophyll concentration was usually lower under G34 glass, ^hicli 

 transmits no radiations shorter than 5290 A. He found that "in all 

 light qualities used the plants increased their chlorophyll concentration 

 with decreasing intensity to a certain point." When plants, from which 

 only the ultra-violet was removed under 65 per cent of the total intensity, 

 were compared with those receiving the full spectrum of daylight under 

 68 per cent intensity, no significant difference in chlorophyll content was 

 found in Geum, sunflower, or Galinosoga. This is the only investigation 

 in which quantitative determinations of chlorophyll were made under 

 various light qualities. 



A relationship between ultra-violet radiation and the development 

 or presence of anthocyanin and related compounds in plant cells has been 

 suggested in a number of cases. Shibata, Kishida, and Nagai (98 to 101) 

 found that the cell sap of epidermal and peripheral parenchymatous cells 

 of the aerial parts of plants in general, commonly contained flavone 

 derivatives. Furthermore, according to them, these compounds were 

 limited almost exclusively to these parts of plants. They also noted 

 that plants in sunny habitats contained greater amounts of flavones than 

 those in shady places, and that alpine plants were richer in flavones than 

 those in lower regions where the intensity of solar radiation was not so 

 great as in alpine regions. In general, plants exposed to intense sunlight 

 showed a greater development of flavones than those under lower 

 intensities unless the plants were protected by some morphological 

 feature such as a thick cuticle. Thus Ficus elastica, a tropical plant grown 

 under strong light intensity, had leaves with a low amount of flavones, 

 but these leaves had a thick cuticle. Rosenheim (81) thought that if 

 the findings of Shibata, Kishida, and Nagai were true, then alpine plants 

 grown at lower altitudes should not contain so much flavone as those 

 grown in alpine regions. Using Edelweiss as an example he found that 

 this plant actually did not develop so much flavone when grown at lower 

 altitudes as when grown in the Alps. 



Schanz (89) noted that much of the red color of red-leaved lettuce 

 grown outdoors disappeared when the plants were placed under ordinary 



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window glass which cut off most of the radiation below 3200 A, while 



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all of it disappeared if wave-lengths shorter than 3880 A were eliminated. 

 When young plants of Celosia Thompsoni with dark red leaves were 

 placed in daylight under various screens the new leaves which formed were 

 less red and more green the more the short wave-lengths were eliminated, 



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and were completely green when wave-lengths shorter than 4200 A were 

 removed. Red-beet leaves lost the red color in the absence of ultra- 

 violet radiation, but the stems and petioles remained red. 



