EFFECTS UPON GERMINATION 



801 



20*C., optimum between 30* and 37''C., and maximum 40°C. Unlike 

 the other pampas grasses mentioned, the germination of achenes of 

 Paspalum dilatatum was not favored by Hght, but was improved by a 

 period in a low-temperature germinator followed by a constant high 

 temperature. They were after-ripened in dry storage, and the speed of 

 after-ripening was increased by drying for several days at 55°C. 



The diverse germination behavior of achenes of these four species of 

 pampas grasses growing in identical habitats indicates that no strict rela- 

 tion exists between the habitat of a plant and its need of light for 

 germination. 



Poa. — In 1878 Wagner (55) found that light had a marked stimulating 

 effect on germination of Poa achenes. Stebler (92) confirmed and 

 extended his results. Nobbe (80) obtained slightly lower germination of 

 Poa achenes in light than in darkness. Because of the importance of the 

 blue grasses in pastures and lawns the effect of light upon germination of 

 these achenes has received the attention of many later investigators. 

 Results are not in agreement, largely because other factors modifying 

 light sensitiveness were not fully investigated, but all workers since 

 Nobbe have agreed that under certain conditions light favors the germina- 

 tion of Poa achenes. 



Jonsson (45) w^as the first to show that the need of light for germina- 

 tion fell as the seeds after -ripened in dry storage. In tests at various 

 dates beginning October 1, 1891, dry-stored Poa pratensis achenes in 

 light and dark at 20°C. gave the following percentage germination: 



Table 3 



Jonsson received similar results with Poa trivialis achenes. 



Reiling (87) confirmed Jonsson's results and showed that the degree 

 of maturity of the achenes at time of harvest as well as the duration of 

 dry storage determined their germination capacity at 20°C. in darkness. 

 Pickholz (84) found that the percentage germination was inversely pro- 

 portional to the water content of the achenes during storage. Hite (44) 

 and Maier (71) also confirmed Jonsson's results on the effect of after- 



