812 BIOLOGICAL EFFECTS OF RADIATION 



Remer (88) and Kinzel (48, 50) found green the most favorable portion 

 of the spectrum for germination. Kinzel reported 10 per cent germina- 

 tion in white light, 55 per cent in darkness, and 93 per cent in green light. 

 Heinricher (35) suggested without any experimental evidence that the 

 inhibiting effect of light on the germination of Phacelia seeds might be 

 due to the fact that white light or the first half of the spectrum reduced 

 the acidity, as in succulents, giving a less favorable medium for lipase 

 activity. He also suggested that light might even destroy the lipase. 



After-ripening Phacelia seeds in dry storage modified their germina- 

 tion in both light and darkness. According to Heinricher (35) freshly 

 harvested seeds did not germinate in hght and only moderately in dark- 

 ness. After 2 months of dry storage there was 4 per cent germination in 

 light, and good germination in darkness. Dry storage in direct sunlight 

 or in darkness was equally beneficial. Kuhn (56) found that seeds 

 stored 6 years in darkness gave 100 per cent germination in darkness 

 against 61 to 92 per cent for new seeds. Seeds stored for 4 years in light 

 followed by 2 years in darkness gave only 64 to 80 per cent germination. 

 Age also modified the behavior toward various portions of the spectrum. 



Remer (88) found 5°C. the minimum temperature for the germination 

 of Phacelia seeds in darkness. Good germination was obtained at 6° to 

 7°C. For germination in light the minimum temperature was 10°C., 

 and the optimum 15°C. A temperature of 20°C. or above was unfavora- 

 ble. Rijof (89) got 90 per cent germination in darkness in 10 days at 

 14° to 16°C. and 64 per cent at 20°C. 



Increased partial oxygen pressure favored germination in light. In 

 75 per cent O2 Axentieff (3) obtained 73 per cent germination in Ught and 

 86 per cent in darkness. In high oxygen pressure many of the seeds 

 germinated backward; that is, the cotyledons grew first. This backward 

 germination was similar to that obtained by Crocker (13, page 272) for 

 the upper achenes of Xanthium, the coats of which restrict the oxygen 

 supply to the embryos. Bohmer (8) claimed that the light-inhibited 

 seeds of Nigella saliva and Phacelia tanacetifolia germinated much better 

 in light in 80 to 100 per cent oxygen than in air, that the light-favored 

 seeds of Epilohium hirsutum, Nicotiana tahacum, Lythrum salicaria, and 

 Elsholtzia germinated better in normal than in increased oxygen pressures ; 

 and that light-indifferent seeds were not affected by increased partial 

 oxygen pressures. Bohmer was certainly incorrect about light-indifferent 

 seeds, for Crocker (13) found the germination of the intact upper achenes 

 of Xanthium was increased by high partial oxygen pressures. Axentieff 

 (3) and Gassner (23) have found also that high oxygen pressures increased 

 the germination of various light-favored seed. 



Kuhn (57) investigated the effect of acid on germination of Phacelia, 

 using filter paper moistened with solutions of various concentrations. 

 Seeds in fight gave 69 per cent germination in 0.1 M HCl and 18 per cent 



