878 BIOLOGICAL EFFECTS OF RADIATION 



renders anatomical differences found of doubtful significance unless they 

 are very marked. 



The effect of ultra-violet radiation alone on anatomical structure is 

 still largely to be determined. Further discussion of anatomical effects 

 will be found in the section of this monograph devoted to this topic 

 (Buchholz, pages 829-840). 



As early as the time of Sachs (85) and DeCandolle (18) ultra-violet 

 has been said to influence favorably flower formation. Eltinge, Ballan, 

 Westfield College reports, Michigan Station reports, and Tottingham and 

 Moore have all suggested earlier or better flowering in certain cases as an 

 ultra-violet effect, but it has already been noted that such effects were 

 not consistently obtained and were usually associated with temperature 

 or other differences when comparisons were made with control plants. 

 Popp found that elimination of practically all ultra-violet had no effect 

 on the time or amount of flowering of many of his plants. In some cases 

 the earlier flowering plants were those from which practically all ultra- 

 violet was screened off. 



ULTRA-VIOLET RADIATION AND THE FORMATION OF CHLOROPHYLL 



AND ANTHOCYANIN 



While Stoklasa (108, 109) noted that exposures not exceeding 2 hr. to 



o 



wave-lengths 3000 to 5000 A of a mercury arc generally caused a rapid 

 development of chlorophyll in etiolated plants, and that etiolated plants 

 exposed to this region of sunlight became green more rapidly than those 

 exposed to full sunlight, Dangeard (15) claimed that blue and violet light 

 from a Nernst lamp seemed to have little influence on chlorophyll synthe- 



o 



sis, and that the energy absorbed below 4900 A was insufficient to bring 

 it about. Sayre (87) has said that with sufficient energy value, chlorophyll 

 develops in that region of the ultra-violet between 3000 and 4000 A. 

 In many reports a deeper green color of plants under one of the special 

 ultra-violet transmitting glasses has been reported, but it should be noted 

 that this is not necessarily an indication of greater chlorophyll develop- 

 ment, as this appearance may be brought about by a more compact 

 tissue, a broken down epidermal layer, lack of hairiness, etc. In addi- 

 tion, as has been indicated before, effects under these special glasses are 

 not necessarily ultra-violet effects. Colla (13) found that chlorophyll 

 developed in plants exposed to radiation of 3300 to 3900 A, the amount 

 being comparable to that produced in ordinary light of low intensity. In 

 none of these cases has there been quantitative determination of 

 chlorophyll. 



Shirley (102) determined quantitatively the amount of chlorophyll 

 developed using the method of WillstJitter and Stoll as modified by 

 Schertz. Plants grown under a blue glass transmitting the region 

 between 3740 and 5850 A under 10 per cent of the total intensity of 



