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GERMINATION AND GAMETOPHYTE OF FERNS. 113 



By the method used by Wiesner, other intensities of light 

 were determined by a comparison of the time required to pro- 

 duce the normal tone with the time taken in bright sunlight. 

 A number of observations were taken of each intensity of 

 light and the intensities given in this paper are the averages 

 of these observations. The intensities are those of sunlight 

 or diffuse daylight, as artificial light was not used; in fact, 

 natural conditions of light were more nearly simulated than 

 <}an be done by artificial light. 



Influence of Light of Different IrjTENsrriES upon Germination. 



Before giving the results of the experiments upon different 

 intensities, the effect of entire absence of light will be given. 



Spores of Dicksonia apiifoUa upon leaf-mold were sowed 

 February 3, 1906, and on February 3, 1907 were examined 

 and found not to have begun germination. This culture was 

 then exposed to light and division took place within about 

 8 days, and in about 20 days the surface was green with the 

 young prothallia. Thus spores were able to germinate after 

 having been in a moist dark chamber for an entire year. 

 Another sowing of D. apiifolia started February 19, was 

 transferred to light September 29, and germinated by October 

 10. A culture of Alsophila pruinata was sowed and trans- 

 ferred to light at the same time as the Dicksonia, and germi- 

 nated by October 8. Sowings of Aneimia phyllitidis and 

 Gymnogramme calomelanos Mertensii were kept in darkness 

 40 days without germination, while the control from the 

 same groups of spores germinated in 10 days. 



Sowings of Asophila pruinata and Aneimia phyllitidis were 

 made upon leaf-mold and exposed to a temperature of 30°- 

 33* C. in darkness during a period of 41 days for the Alsophila 

 and 40 days for the, Aneimia. Neither germinated in the 

 absence of light even at the higher temperature. The 

 Alsophila culture was transferred to light, and germinated in 

 11 days, while the control of the Aneimia germinated in about 

 10 days in light. 



In 0.5% Knop's solution in darkness at 30° -33' C, a sowing 

 of Gymnogramme calomelanos Mertensii germinated in 20 



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