EFFECTS UPON GERMINATION 813 



in distilled water; in darkness they gave 80 per cent germination in 

 distilled water. Acids lowered germination in darkness and stimulated 

 it in light. HCl, HNO3, and H2SO4 had similar effects in like concentra- 

 tions. According to Magnus (70) acid treatment caused "false germina- 

 tion"; that is, the embryos broke through the coats without growth. 



Magnus rinsed from intact seeds of Phacelia tanacetifolia a substance 

 which when applied to the same sort of seeds inhibited their growth in 

 weak light, but not in darkness. This substance was fluorescent, heat- 

 stable, water-soluble, and alcohol-insoluble. He pointed out the fact 

 that low concentrations of fluorescent substances are toxic to organisms 

 in light, owing to their photochemical effects. Since darkening the 

 chalazal end of intact seeds or removing the coats from that region per- 

 mitted germination, Magnus concluded that the fluorescent inhibiting 

 substance was largely located in the chalazal end of the coat. He also 

 obtained from the radicle of Phacelia and the leaves of Pelargonium a 

 water extract that inhibited germination of Phacelia seeds in light but 

 not in darkness. A water extract from Epilobium seeds showed no 

 inhibiting effect. 



Peters (83) largely confirmed Magnus' results except in two respects. 

 Peters found that the substance inhibited the germination of Phacelia 

 seeds slightly, even in darkness, if the washings were first exposed to light, 

 and that the effective agent was not identical with the dark-brown water 

 extract obtained from the coats but was a whitish opalescent material. 

 He considered the joint effect of Hght and the fluorescent pigment on the 

 germination of Phacelia seeds as photocatalytic, while Magnus was 

 uncertain about how they acted. Axentieff (2, 3, 4) studied the effect 

 of the rinsings from several sorts of light-favored and light-inhibited seeds 

 on the germination of the same or other species. His results were quite 

 varied. Some extracts inhibited germination in both light and darkness; 

 others stimulated germination in some seeds and inhibited it in others; 

 and in one case the extract causing inhibition was not fluorescent. Axen- 

 tieff also found that proper abrasion of the coats would induce perfect 

 germination of Phacelia seeds in light and darkness. Abraded seeds gave 

 98.8 per cent germination in light and 98 per cent in darkness, and intact 

 seeds gave 31.8 per cent in light and 92 per cent in darkness. Bohmer (8) 

 showed that on removal of the coat over the radicle the seeds grew nor- 

 mally, with the root emerging first, in both light and darkness. On 

 removal of the coat at the other end, the epicotyl grew first, and the 

 seed germinated equally well in light and darkness. Removal of a por- 

 tion of the coat on the sides of the seed did not induce germination in 

 light. The naked embryos germinated equally well in light and darkness. 



The work of Axentieff and Bohmer threw some doubt upon the con- 

 clusions of Magnus and of Peters that light inhibition of Phacelia was a 

 photocatalytic action. They showed that the seed coats of Phacelia 



