870 BIOUX}ICAL EFFECTS OF RADIATION 



being constant. Yet the majority of investigators who have used these 

 new glasses have placed the emphasis almost exclusively on their rela- 

 tively greater ultra-violet transmission. 



Many of the experiments conducted with these new glasses have not 

 been carefully controlled aside from radiation conditions, so that results 

 are correspondingly inconclusive. The fact that a small number of 

 plants was used in many cases is also unfortunate, and failure to repeat 

 experiments still further reduces the value of results obtained, since 

 very often those who have repeated their experiments were unable 

 to duplicate their original results. Most of the experiments of this type 

 have been carried out from a practical viewpoint by greenhouse keepers, 

 horticulturists, and floriculturists with practical results rather than 

 scientific data as the aim and purpose. 



In this country one of the carefully performed experiments of this 

 nature was carried out at the Boyce Thompson Institute (Arthur, 2). 

 Several species of flowering plants were grown under Uviol glass which 

 transmits 80 per cent at the extreme ultra-violet of sunlight, and no 

 differences were observed in growth habit, time and amount of flowering, 

 or amount of green tissue produced as compared with plants grown under 

 ordinary greenhouse glass. "We have yet to find any distinct advantage 

 to the plant in growing it under a glass which transmits the extreme 

 ultra-violet region of sunlight." 



Osmun (63, 64) obtained favorable results under vita glass for lettuce 

 and radish one year, but during the next year continued experiments gave 

 contradictory results. The first year, radishes under vita glass showed a 

 gain of 71 per cent in weight of the entire plant and 124 per cent in 

 weight of roots as compared with an equal number of plants under 

 ordinary glass. Similarly lettuce gained 76 per cent in weight and 

 formed more compact heads under vita glass. The next year radishes 

 averaged 10 per cent less in weight under vita glass than those under 

 ordinary glass in one test and 14 per cent more in another. Lettuce 

 under ordinary glass this second year weighed 3 per cent more than that 

 under vita glass. Obviously nothing concerning ultra-violet radiation 

 can be concluded from these results. 



Tottingham and Moore (115, 116), and Tottingham (114) have 

 reported on some horticultural investigations at the Wisconsin Agri- 

 cultural Experiment Station. In the principal paper (116) a small 

 number of plants of 12 different species which had been under vita glass 

 for a number of weeks was compared with plants similarly treated but 

 grown under window glass. The comparisons involved the nature and 

 amount of growth, dry weights, and partial chemical analyses. As stated 

 by the authors, "The present investigation is concerned with the elimina- 

 tion of a small portion of ultra-violet (about 3100 to 2900 A) in sunlight 

 by the screening effect of common glass," but there is no mention in the 



