162 



appeared to be incapable of germination by the method 

 described, whilst the rest showed great différences in 

 germination so that seeds of equal development had to 

 be selected most carefuUy for each vessel. 



Cultivation took place in the laboratory glass-house, in 

 which the température was not constant (about 20") and 

 generally ranged over a few degrees. After the seeds had 

 been planted in the vessels, the latter were placed in a 

 box, covered with black cloth, so that they were com- 

 pletely in the dark. Thèse boxes were regularly ventilated 

 for otherwise the seedlings did not grow quite perpen- 

 dicularly in conséquence of the impure air. 



This précaution was also adopted for the same reasons 

 by Miss De Vries^). After thèse four days the length 

 of the coleoptiles of Avena reached IV2 to 2 cm., whilst 

 the hypocotyls of Sinapis seedlings attained a length of 

 about 1 '/o to 3 cm. Oblique growths and too long or 

 too short seedlings, were removed before the boxes were 

 used for experiment. 



The Thermostat. 



The thermostat necessary for this investigation was made 

 according to my spécifications by Mr. Roelink, attendant 

 at the Botanical Laboratory. It consisted of an outer and 

 inner box (PI. XV. XVI and XVII). The outer box had 

 a height of 300 m. m., a breadth of 295 m. m., and a 

 depth of 145 m.m. For the inner one thèse dimensions 

 were respectively 240, 220 and 65 m.m. The two bottoms 

 and back walls were of copper, the fronts and the right 

 and left side walls of glass. The lid of the inner box was 

 also of copper, whilst the outer box was open on top. 



^) Marie S. de Vries. Der Einfluss der Temperatur auf den Photo- 

 tropismus. Recueil des Trav. botan. Néerland. 1914, Vol. XI, p. 200. 



