1100 BIOLOGICAL EFFECTS OF RADIATION 



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X2800 A on Spirogyra, Cladophora, Nitella, and Tradescaniia. Kluyver 

 (32) found decomposition only after 55 to 60 hr. of irradiation with a 

 mercury arc, and he beUeves that Schulze's experiments are very con- 

 clusive, since the ultra-violet radiation actually reached the chlorophyll 

 without decomposing it. Kluyver also reports no change if extracted, 

 dried, irradiated, and redissolved chlorophyll is used. Stoklasa and 

 coworkers (75) report the stability of chlorophyll solutions in ultra- 

 violet light. Ursprung and Blum (79) found that the cells of green 

 leaves from Vicia Faba are more resistant to ultra-violet light than 

 those of etiolated leaves. Hertel (25) observed less damage done to 

 chlorophyll-containing cells of Elodea and Vallisneria if visible and ultra- 

 violet radiation are used simultaneously. While these authors emphasize 

 the stability of chlorophyll in the living chloroplasts as well as in the 

 form of solid precipitated material, or in concentrated or dilute alcoholic 

 solutions, other authors come to the opposite conclusion. Bierry and 

 Larguier des Bancels (4) reported decolorization of alcoholic chlorophyll 

 solutions under prolonged irradiation with two mercury arcs. A recent 

 publication by Richter (57) deals in part with chlorophyll decomposi- 

 tion under the influence of the quartz mercury arc. Richter uses the 

 "Kiinstliche Hohensonne, Original Hanau" and finds that by f^-hr. irradi- 

 ation of leaves or parts thereof (from Tropaeolum, Robinia Pseudacacia, 

 and 7m florentina) destruction of the chlorophyll has taken place, as 

 indicated by the distinct yellow coloration characteristic of xanthophyll. 

 Richter also finds that the chlorophyll destruction in irradiated autumnal 

 leaves of Tropaeolum majus is smaller than in summer leaves and he 

 explains this by the increased thickness of the epidermis and its resistance 

 to radiation. In fall leaves the beginning decomposition of chlorophyll 

 was studied by means of the fluorescence color analysis (analysis attach- 

 ment to Bach's mercury lamp). This method allows differentiation 

 of the degree of decomposition: it was found that the decomposition 

 is more distinct in irradiation through the lower than through the upper 

 epidermis. Richter observed that parts of yellow fall leaves exposed 

 to light X < 3000 A show deep green color owing to chlorophyll, while 

 the unexposed parts remained yellow. For this preservation of chloro- 

 phyll in the autumnal leaves Richter gives two explanations: (I) Inter- 

 ruption of the communication of the sieve tubes, e.g., due to precipitation 

 reactions under the influence of ultra-violet light. Such a process 

 would prevent the transportation of chlorophyll decomposition products 

 and would fit well into Stahl's work (71) on interruption of sieve tubes 

 and into Molisch's ideas (43). (II) If the autumnal decomposition 

 of chlorophyll is caused by an enzyme, the complete destruction of this 

 enzyme by ultra-violet light would account for the preservation of 

 chlorophyll. The well-known red fluorescence of the chloroplasts 

 (Gicklhorn, 22) is only visible in parts of the leaves or in solutions which 

 have been protected from ultra-violet irradiation. 



