LIGHT AND GERMINATION 



427 



ripened seeds show good germination in about four days ; 

 if after two days in the light, when no germination has 

 occurred, the seeds are transferred to the dark, a consider- 

 able percentage germinate subsequently ; the effect of the 

 Hght persists. If after-ripened seeds are kept in suitable 

 conditions for germination (moist at 33" C), but in the 

 dark, for about a week, subsequent germination in light is 

 very much depressed ; a secondary dormancy is induced, 

 very much resembhng that of the Brassica seeds already 

 described. The blue end of the spectrum is effective, the 

 red end acts as darkness. The seeds germinate in the dark 

 in rich soil, on Knop's solution, or in presence of nitrogenous 

 compounds, especially of nitrates and nitric acid. They 

 germinate in the dark if exposed to alternating temperatures, 

 e.g. 22 hours at 20° C. and 2 hours at 34° C. If the seeds 

 are not fully after-ripened there is a beneficial action of 

 light at 34° C, but not at 16° C. 



Lehmann (191 1) found that the "light" seeds of 

 Epilohiiim roseum, and some other plants, would germinate 

 in the dark if exposed to a sudden rise of temperature, while 

 Gassner (1915a) found that they would germinate with 

 alternating high and low temperatures, Lehmann (19 12) 

 found that, within the limits of temperature favourable to 

 germination, certain " light " seeds would germinate in the 

 dark at high temperatures, and certain " dark " seeds 

 in the light at low temperatures. This is illustrated in 

 Table XXXV. 



TABLE XXXV 

 Relation of Light and Temperature to Germination 



