EFFECTS UPON GERMINATION .811 



there is no doubt he has classified many seeds as requiring or being favored 

 by hght that under other conditions would germinate perfectly without 

 light. Of the 964 sorts tested, 343 required light or were favored by light, 

 128 were favored by darkness, 271 responded to light and severe frost 

 ( — 20°C.), 95 to darkness and severe frost, 58 required light and mild 

 frost (—2° to 2°C.), 34 darkness and mild frost, and 35 were indifferent. 

 Of the 964 sorts used, 69.7 per cent were light-favored, 26.6 per cent dark- 

 favored, and 3.5 per cent indifferent. 



SEEDS THAT ARE INHIBITED BY LIGHT 



Phacelia tanacetifolia. — As previously mentioned, Phacelia tanaceti- 

 folia seeds were amongst the first investigated (88) in which germination 

 was hindered by light. These seeds have been more studied than any 

 other light-inhibited seeds as to their light sensitiveness and the effect 

 of other factors upon their light sensitiveness and germination. All the 

 authors cited in this section agree that light reduced the speed and total 

 germination of the intact seeds, and that the inhibiting effect increased 

 with rise in light intensity. 



The investigators usually w^orked with daylight, which meant large 

 variation of light intensity and exposure of the seeds to darkness every 

 night. The darkness, of course, favored germination. Remer (88), 

 who first studied the effect of light on Phacelia tanacetifolia seeds, found 

 that direct sunlight greatly hindered germination and that the inhibition 

 lessened as the light intensity decreased. Magnus (70), using 1-year-old 

 seeds, obtained 90 per cent germination in darkness, 4 per cent at a north 

 window, and 40 per cent 1 meter from a north window. 



Kuhn (56) and NikoH(5 (78) employed constant and continuous 

 artificial light sources. In Kuhn's experiment hght with intensities of 

 380, 133, 84, and 64 N. K. produced "lichthart" seeds in a few days; 

 that is, so changed the seeds that they would not germinate later in dark- 

 ness. With an intensity of 40 N. K., 28 per cent germinated in 4 days 

 and the rest became "Hchthart," while 68 per cent germinated in the same 

 time in darkness. Nikoli6 showed that the inhibition increased with 

 light intensity following a hyperbolic curve. A constant light of 0.8 

 H. K. intensity decreased germination 30 per cent. Previous exposure 

 of the seeds to light inhibited germination in darkness, the degree of 

 inhibition increasing with the duration of exposure and intensity of the 

 light ; likewise, a period in a dark germinator before illumination reduced 

 the inhibiting action of light, the effect increasing with length of the 

 dark period. 



The region of the visible spectrum that hinders germination of Phacelia 

 tanacetifolia seeds has had some attention. According to Heinricher (35) 

 germination was hindered by w^hite light and the less refrangible half 

 of the spectrum, and favored by darkness and the more refrangible half. 



