856 BIOLOGICAL EFFECTS OF RADIATION 



From brief reports in Gardeners' Chronicle for 1927 and 1928 by 

 Maddock (49), Russell (83), and the Kew Gardens (42) it appears, in 

 general, that better results were obtained in houses covered with the 

 English vita glass, which also transmits all wave-lengths of daylight 

 ultra-violet, than in houses covered with ordinary window glass, which 

 transmits only down to about 3130 A. The source of radiation in these 

 experiments was daylight only. Russell states that seeds and seedlings 

 when screened with vita glass germinated earlier and showed taller and 

 sturdier growth than did those under ordinary glass, but no definite 

 data are given in his report. In the Kew Gardens report it is stated, 

 regarding germination that "the first lap of the race between two sets of 

 seeds and plants . . . has ended in victory by 24 hours for those grown 

 under the new glass which admits the ultra-violet rays of the sun." The 

 mistake made in all these papers is that of attributing the results to one 

 variable, ultra-violet, when many other variables such as temperature, 

 total-radiation intensity, visible radiation, and infra-red radiation, also 

 existed. 



Jacobi (40), after giving an extensive review of literature dealing 

 with general effects of ultra-violet radiation, presents the results of his 

 own experiments, somd of which were concerned with seed germination. 

 Radish, mustard, and lettuce seeds were selected for this work because 

 they were thought to give better germination in the dark than in the 

 light. A mercury-vapor lamp was used as the source of radiation. By 

 the use of glass and solution screens all other regions of the spectrum 

 were eliminated except the region between 3000 and 4000 A. When dry 

 seeds were exposed to this region for periods of 8, 16, 24, and 32 hr., no 

 marked effect was produced on germination except that the mustard 

 irradiated 24 hr. and the lettuce irradiated 32 hr. seemed to be furthered 

 in growth after two days. Soaked seeds, on the other hand, irradiated 

 for 2, 4, 6, and 8 hr. were reported to give a somewhat higher rate of 

 germination. Exposures of soaked seeds for 10 hr. reduced the rate of 

 germination. Seeds irradiated after the emergence of the radicle were 

 unaffected by irradiations of 2, 4, 6, 8, or 10 hr. 



An examination of the data in which favorable effects of the radiation 

 seem to have occurred shows wide variations and fluctuations in the rate 

 of germination of irradiated plants as compared with controls. For 

 example, after 66 hr. the average percentage germination of lettuce 

 irradiated for 2 hr, was 65.5 while that of the control was 63.75 per cent, 

 but this same seed irradiated for 4 hr. gave 63.5 per cent germination 

 in the same time, while the control gave 68.5 per cent. Furthermore, 

 there is no consistent correlation between time of irradiation and effect. 

 In one instance the 2-hr. exposure gave the highest rate; in another the 

 6-hr. one; in still another, the 8-hr. one. While in many cases the 

 controls were somewhat behind the irradiated plants in rate of germina- 



