806 BIOLOGICAL EFFECTS OF RADIATION 



and 19°C. (20 hr. daily) gave only 60.5 per cent germination in 

 light. 



The latent light effect was easily demonstrated with these seeds, since 

 they could be exposed to light at 28°C. without germination. The 

 imbibed seeds were exposed to light for various periods, then dried for 



3 to 7 days in darkness, and finally placed in dark germinators at favorable 

 intermittent temperatures. Those that had been in a dark germinator 

 before drying gave 14 per cent germination, those previously exposed to 

 diffuse daylight, 61 per cent, and those previously exposed to continuous 

 artificial light of 600 N. K.^ intensity 70 per cent germination. The 

 effect was shown even after a week's drying. Gassner concluded that 

 light did not act as a releasing stimulus on this seed, but that it caused 

 biochemical changes which remained effective even after considerable 

 periods of drying. 



Lehmann (60), Ottenwalder (81), and Gassner (26) found that dilute 

 HCl and H2SO4 did not force Ranunculus sceleratus seeds, and Lehmann 

 observed that solutions of H2O2 and Fe2Cl6 had no action. On the other 

 hand, Lehmann found 1 per cent Knop's solution very favorable to the 

 germination of these achenes in darkness at 20°C. ; he got 80 to 92 per cent 

 germination in darkness with Knop's solution, per cent in darkness 

 with water, and 78 per cent in light with water. Knop's solution was not 

 effective at 15°C. Gassner (26) later found Knop's solution very effec- 

 tive in darkness both above and below 20°C., especially when favorable 

 intermittent temperatures were used. Gassner showed that the favorable 

 action of Knop's solution was due to its nitrate content and that other 

 salts of the solution were without influence. Various other nitrogen 

 compounds (nitrates, nitrites, ammonium salts, nitric acid, and urea) 

 were effective also. Lehmann (60) concluded that the action of soils in 

 forcing germination in darkness was due to the soluble nitrogen com- 

 pounds present. 



Onagraceae. — Kinzel (51, page 46) stated that seeds of the family 

 Onagraceae were light-favored. Considerable work has been done on 

 several species of Epilohium and some work on Oenothera. Kinzel 

 found that alpine species of Epilohium were slow to germinate. One 

 lot of E. trigonum seeds (50) gave 100 per cent germination in light in 



4 months and 53 per cent in darkness in 11 months. In another lot (51, 

 page 46) germination was completed in light after 6 months and in 

 darkness after 18 months. Niethammer (75) found seeds of E. parvi- 

 florum light-obligates, even after 6 months of dry storage. Fresh seeds 



* The German authors cited in this paper have used three different Ught units: 

 Normal German candle, N. K.; Hefner candle, H. K.; and Meter candle, M. K. The 

 values of these in international foot-candles are: N. K. = 1.11 international foot- 

 candles; H. K. = 0.9 international foot-candle; and M. K. = 0.0926 international 

 foot-candle. 



