481 



It may be noticed how great the difference is between the two 

 halves of the revolntion, while this difference disappears beyond tiie 

 arrow, indicating the moment at which (lie excentric load is removed. 



II refers to the clinostat of van Hakrevkld; here the excentric 

 load was larger, 1.6 KG., calculated on the axis and there too 

 irregularities appear, which are soinelinies very considerable. The 

 ar)-ow indicates the moment at which the excentric load was 

 increased to 2 KG. The clinostat had come to a stop ; this happened 

 with a clock-weight of 13 KG. If a heavier weight had been 

 chosen, the njovement would of course have continued. Aftei- 

 removing every excentric load, the running was perfectly regular, 

 as appears from the rest of the figure. 



III shows the working of the clinostat dk Boutkr with an excentric 

 load of 26 KG. calculated on the axis. We see that notwithstanding 

 this, it runs quite regularly, so that the superiority of this clinostat 

 is perfectly clear from the figure. 



A contemplation of the time-signals T in the three parts of the 

 figure will necessarily lead to the same conclusion; these time- 

 signals gave a sign after every six minutes. 



Summai'izing I arrive at the conclusion, that this clinostat is a 

 great improvement on those hitherto used. Now that plant-physiology 

 is developing more and more into an exact science, the old "a pen 

 pres" methods will have to be left and therefoi-e care should be 

 taken that the instruments used come up to high requirements of 

 precision. 



Utrecht, Botanical Laboratory, December 1922. 



