25 



theless the growth of the hypocotyls caused me much 

 trouble even hère. Therefore as soon as the atmospheric 

 température permitted it, I put the growing-boxes out of 

 doors and then I ahvays had qui te straight seedlings. This 

 last point is the strongest argument in favour of my idea, 

 that want of fresh air was the cause of ail my trouble. 

 During the growth in the hothouse or in the dark room 

 the température was registered by meansof athermograph. 

 Nearly always the température varied between 18° C. and 

 22° C, a few times only it was higher and then for a 

 short tlme only. 



§ 6. Apparatus and dark room. 



The thermostat. 



The spécial requirements to be fulfllled by a thermostat 

 fit for this investigation, were the cause that not one of 

 the existing types could be used. Therefore a new ther- 

 mostat constructed ') according to my spécification was 

 obtained by the ^Botanical Laboratory of the University 

 of Utrecht. The extraordinary kindness and libcrality of 

 Professor Went, who put a sum at my disposai from the 

 grant of the laboratary made it possible to give the 

 thermostat ail the qualifies I thought necessary for my 

 experiments. 



The manner of heating and the régulation of the tem- 

 pérature were imitated from the apparatus used in the 

 van 't Hoff-laboratory at Utrecht. ") To the mechanician 

 of that laboratory, J. W. de CTroot, I owe much helpful 

 information. The requirements which the thermostat had 

 to fulflU were the following: 



1) The thermostat was constructed by D. B. Kagenaar sr., 

 van Wijckskade, Utrecht. The total cost was about 200 guilders, 

 thermoregulator, stirring apparatus and lamps included. 



2) A description oT this apparatus is to be found in C. Eu won. 

 Piëzochemische onderzoekingen. Diss. Utrecht. 1910. 



