Physiological Studies on Schistostega osmundacea. 19 



heliotropism of the filaments of the protonema was clearly observ- 

 able in the dish put in the former bottle (Fig. 5), while in the 

 latter no such phenomenon conld be seen. This result coincides 

 with the well-known fact that the heliotropic cm'vatnre occurs 

 more strongly in blue light than in any other coloured light.' ^ 



IV. Influence of Temperature. 



Camille Seevettaz (8) found that a temperature between 16^ 

 and 25^0. is most suitable for the species of moss he studied ; 

 that those species cease to grow when the temperature is above 

 45°C. ; and that a temperature between 15^ and 16^0. is required 

 for the formation of buds and leafy shoots ; more heat being re- 

 quired for this than for the development of the protonema. In 

 my observations of Schistostega in its natural state, a temperature 

 between 19° and 2 PC. seems to suit it best. The temperature in 

 September and October, 1914, was between 15° and 25°C. in the 

 laboratory, and the moss was observed to produce leafy shoots 

 abundantly. The moss placed in my hot house, the temperature 

 of which was carefully kept between 16°- and 25°C., continued 

 to produce shoots. I have observed the development to stop 

 at 2°-6°C. 



Eesistance to lower temperature. — To ascertain the lowest 

 temperature the moss can stand, I took a wide -mouthed cylindrical 

 Dewae flask and put a test tube into it containing the moss 

 with a thermometer inserted. Filling the flask with a mixture of 

 snow and salt, and covering it with a close-fitting lid so as to 

 allow the upper half of the thermometer to protrude from the lid, 

 the temperature of the test-tube began to fall. When it reached 



1) Pfeffee, W. : Pflanzenphysiologie, II. Aufl. BJ. Il , p. 577. 1904. 



