45 



in tlie Physical Laboratory. In the flrst place the time 

 needed to bring the air inside the thermostat to a certain 

 température was determined, and second! y what time the 

 mould inside the vessels needed for this purpose. The 

 coleoptiles of Avena were too small to use thèse for the 

 experiment. 



When the différence of température between the water 

 of the thermostat and the mould in the vessel was 15° C. 

 at the beginning, the air inside was at quite the same 

 température as the water after 45 minutes, and the mould 

 was still 0.4° C. behind aftêr 45 minutes, and 0.1 C. after 

 60 minutes. As the coleoptiles are heated more slowly 

 than the air, but faster than the mould, they were less 

 than 0.1° C. behind the température of the water after 

 one hour. In comparison with the sources of error from 

 other expérimental conditions this time of preliminary 

 warming was quite sufôcient. No experiments were made 

 in which a shorter. preliminary time was allowed. 



HUMIDITY. 



Nowhere has an influence of humidity upon the pre- 

 sentation-time been noticed; but I must add, that this 

 influence has not been investigated. On the contrary, I 

 tried to keep the humidity as constant as possible and 

 within the thermostat the air was always saturated with 

 vapour, as part of the bottom was covered with water. 



LiGHT USED. 



Ail observations were made at the same place in the 

 dark room and with the same red light. To this end an 

 ordinary electric lamp was used, placed under a glass-bell 

 after Sachs, filled with a saflFranin solution of 2 7oo. ') 



The constancy of the red light was no superfluous 

 précaution as is shown by the following experiment. A set 



1) cf. A. H. B 1 a a u w, 1909, p. 78. 



