GENETIC AND CYTOLOGICAL EFFECTS 279 



in a wide range of doses (1.8 X lOMJo.O X lO'' ergs/mm^), gave signifi- 

 cant increases over the control, but no significant differences between 

 doses. A dose of 65 X 10^ ergs/mm- at wave length 302 m/x and one of 

 120 X 10^ ergs/mm- at wave length 313 m/x quadrupled the spontaneous 

 frequency. From these results the conclusion was drawn that the peak 

 of genetic effectiveness was in the neighborhood of 300 mfx. Supporting 

 this hypothesis was the demonstration that a suspension of Antirrhinum 

 pollen in 30 per cent alcohol had a maximum of absorption around 300 vay.. 



Comparable data by Stadler and Uber (1938) for the frequency of 

 endosperm deficiencies induced by monochromatic radiations also showed 

 effects in large numbers for all wave lengths tested in the range 235-302 

 mM- Longer wave lengths had no appreciable effect. The frequency of 

 germless seeds was increased markedly by radiation of wave lengths 280 

 van and shorter, but not by longer wave lengths, even at much higher 

 doses. The tabular data on which these conclusions were based were 

 later published (Stadler and Uber, 1942, Table I), together with the 

 results of additional experiments on relative wave-length effectiveness. 



The frequency of induced effects was higher for wave length 297 m/x 

 than for 2G5 m^i, as in the experiments of Noethling and Stubbe. But, 

 though wave length 297 m/x significantly excelled 265 van at the higher 

 doses, the relation was clearly reversed at the lower doses. Both wave 

 lengths were tested at doses of approximately 1, 2, 3, 6, and 12 X 10' 

 ergs/mm^ While the longer wave length was about twice as effective as 

 the shorter in comparisons made at the heaviest dose, it showed no effect 

 at the lowest dose, and only about one-fourth of the wave length 265 m^u 

 effect at the second dose. The results as a whole showed that there were 

 wide differences in the dosage relations at the different wave lengths 

 tested, and that a study of the dosage relation and of internal filtration 

 was needed before the relative effectiveness of the wave lengths could be 

 estimated. The results of these studies were summarized in the preceding 

 section. 



The most reliable indications of relative effectiveness come from com- 

 parisons made at low doses. However, at the lowest doses filtration 

 losses are still effective and require correction. The frequency of endo- 

 sperm deficiencies produced in an experimental comparison of seven wave 

 lengths, all at a dose of 2 X 10-^ ergs/mm^, seriated for the control of 

 daily fluctuations, is shown in Table 7-7. 



At this dose, the endosperm deficiencies induced by wave lengths 265 

 and 254 m^ix are about 3 times as frec^uent as those induced by wave 

 length 297 m^i and about 15 times as frequent as those induced by wave 

 length 302 m^u. When the dose is increased to about 8 X 10' ergs/mm', 

 the differences are much less pronounced and in some cases hardly signifi- 

 cant. The evidence on internal filtration, subject to the approximations 

 which have been mentioned, indicates that wave lengths 265 and 254 in/u 



