1062 



BIOLOGICAL EFFECTS OF RADIATION 



Ultra-violet Rays. — Of the relationship between respiration and ultra- 

 violet radiation we have almost no knowledge because the necessary 

 experiments have not been performed. There has been but one report 

 of measurements in this field, and even before it has been repeated by 

 others, there has been adverse criticism of its conditions and technique 

 by Popp and Brown (14, pages 169-171) in their critical analysis of 

 recent work with ultra-violet. 



The report in question was made by Masure (11) who used germi- 

 nating pea seeds and screened radiation from a mercury-vapor lamp. 

 The Corning G586AW screen was said to transmit chiefly rays in the 

 region 3650 A, which is not far below the visible rays at 4000. However, 



Irraclici+ion 

 period 



Irradiation 

 period 



^^ 60 

 " 50 



10 20 50 40 50 60 70 80 90 100 110 120 150 140 150 160 110180 190 200210220 250240250260270 



Time in MInu+es 



rradiation 



Fig. 1.- 



10 20 30 40 50 60 70 80 90 100 110 120 150 140 150 160 110 180 190 200 

 Time in Minu+es 

 -Effect of raying on the rate of respiration of etiolated pea seedlings. 



Masure, 11.) 



(After 



Popp and Brown claim that this filter also transmits infra-red even 

 better than ultra-violet and thus challenge any evidence derived from its 

 use as a test of the influence of ultra-violet on either growth or respiration. 



The results obtained by Masure for the effect on respiration are 

 shown in the above graph taken from his paper. It shows clearly that 

 the rate of respiration is temporarily increased by the rays which pass 

 the filter and ultra-violet is at least a part of this effective radiation. 

 Its effects disappear soon after it is discontinued. The preliminary 

 drop in respiration soon after the radiation is applied is said by Masure 

 to represent an expansion of the seeds as they are heated by the rays 

 which they absorb. This is possible because the respiration is measured 

 as O2 consumption read from the movement of a column of liquid in 

 equilibrium with the gas pressure within the experimental chamber. 

 However, this heat effect must also influence the production of CO2 

 and the consumption of O2 throughout the period of irradiation. 



Only two of these experiments have been reported. In view of the 

 small amount of evidence here and the lack of confirmation of it else- 

 where it must be said that we do not know yet just how ultra-violet 



