858 BIOLOGICAL EFFECTS OF RADIATION 



That variations between test plants and controls other than the 

 presence or absence of ultra-violet radiation did occur in Masure's 

 experiments is very probable. Certain measurements of the radiation 

 used by Masure, made in our laboratories with a Kimball and Hobbs 

 pyrheliometer, indicate this. A sample of G586AW glass of the type used 

 by Masure gave a total transmission of 10.71 per cent of the radiation 

 from a Cooper Hewitt mercury-vapor arc. When a sample of Noviol 

 "0" glass was interposed between the mercury arc and the G586AW 

 screen, the transmission was 7.14 per cent of the energy incident on the 

 Noviol "0" screen. Since the Noviol "0" glass transmits practically 

 no ultra-violet, the 7.14 per cent transmission of these two glasses together 

 must represent energy in the visible and infra-red, though chiefly in the 

 infra-red, since the G586AW glass transmits only very feebly in a small 

 part of the extreme visible red. Since the transmission of G586AW alone 

 was only 10.71 per cent of the total energy of the mercury lamp and since 

 when all ultra-violet was removed the transmission was still 7.14 per cent, 

 it is obvious that the ultra-violet transmission of G586AW could not 

 exceed 3.5 per cent. If the absorption of infra-red by the Noviol "0" 

 glass were taken into account, this figure would be reduced still further. 

 When we consider that a large part of the energy from a mercury arc is 

 in the ultra-violet, and that when all this is eliminated the G586AW 

 filter still transmits 66 per cent as much energy as it does when the ultra- 

 violet is present, we must conclude that the G586AW screen transmits 

 infra-red better than it transmits ultra-violet. If then we get differences 

 in germination under this screen, it is hardly justifiable to attribute them 

 to ultra-violet unless we have supplied our controls with an equal amount 

 of infra-red. In any case we can hardly agree with the author that his 

 experiments were conducted in the absence of all other radiations than 

 ultra-violet. While it is possible that very small differences in the ultra- 

 violet might be more effective than large differences in the infra-red, we 

 cannot be certain of this until it has been demonstrated experimentally. 

 If, as in the case of Masure's experiments, the differences are so slight 

 as to require statistical manipulation to bring them out, we can reasonably 

 doubt that the ultra-violet was very effective. 



It might further be mentioned that some of the significant figures are 

 based on averages of seedlings which received exposures ranging from 

 15 min. to 72 hr. This is not a very satisfactory grouping of data. In 

 other cases individual series were analyzed. One would expect that if 

 the ultra-violet is the effective agent in producing beneficial results, there 

 would be some relation between time or intensity of exposure and the 

 effect produced. Yet no relation is apparent. 



Masure's experiments were conducted with seeds in closed dishes 

 placed at distances of 8.5, 17.5, and 18 cm. from the mercury arc lamp. 

 It is difficult to understand how a fan alone would prevent heating effects 



