165 



Arrangement of expérimental objects. 



The boxes containing the seedlings of Avena were, 

 immediately after planting, packed in absorbent gauze in 

 order to prevent the soil from faUing out when rotating 

 on the dinostat. The boxes were fastened into the clamp 

 arranged for this purpose, in such a way that the seed^ 

 Hngs were perpendicular to the horizontal axte of the 

 dinostat, by which arrangement the geotropic and pho- 

 totropic stimuU were so appHed that ail curvatures occurred 

 in one and the same plane, namely in that of rotation. 

 In short experiments — such in which the seedlings had 

 only a short fore-period in nitrogen — the seedlings were 

 rotated on the dinostat before stimulation, This could be 

 done with two boxes at a time, fastened into the clamp 

 with their bottom-walls against each other. 



Since on account of the cotyles dicotyledonous seed- 

 lings cannot grow through absorbent gauze, the boxes of 

 Sinapis were not rotated on the dinostat, but were simply 

 placed in a vertical position after being stimulated. Of 

 course thèse experiments could never be carried out with 

 two boxes at a time. 



The Nitrogen. 



As I needed large quantities of nitrogen, I obtained it 

 from the métal cylinders of commerce. Thèse were found, 

 however, to contain a fairly considérable proportion of 

 oxygen, which I estimated with a phosphorus pipette ^). 

 As an average of several déterminations I found 3.3, 4.3 

 and 4.7 % oxygen in the three cylinders which I successively 

 used. In order to absorb the oxygen, the nitrogen was 



M Prof, van Romburgh was kind enough to allow me the loan of 

 this apparatus. 



