414 



olt air-tight and leakage is impossible, because lliere never arise 

 great ditfereiices (if pressure in the vessel. In the middle of the 

 loose part h there is a cavit^y, in which k., can rotate freelj. When 

 .VI is slowij rotated by a motor, <(, will transmit this movement 

 by means of the teeth /a, and ta to «,, which causes the circulaling 

 air to be equably distributed over the whole vessel, in consequence 

 of which the germplants are constantly surrounded by fresh air. 

 The necessity of ventilalion lu n cylindrical respiratory vessel (dia- 

 meter J5 cms., height 20 cms.) was immediately apparent from one 

 of the many test experimenis. At a constant temperature of 20° C. 

 the O^-absorptioii caused in 50 mins. a height of 4 cms. on the 

 manometer lll^. Ne.xt a quicker circulation of JO mins. duration 

 followed, causing an equal rise of the manometer as before in 

 50 mins. No oilier explanation of this could be found, Imt the 

 oi'cni'rence of a CO, iiccnmiilaiion in the vessel. This was supposed 

 to lie due to the fact, thai ilie air entering at vi passed by the 

 easiest loiile through the vessel to the exit vUy taking with it only 

 part of the CO,. When in consecpience of a more rapid circulation 

 part of the accumulated CO, disappeaied, this explained a sudden 

 greater rise of the manomeler-. As soon as the rotaiy movement of 

 the respiring objects, pieveiiled all CO,-accumulalion in the vessel, 

 there was inileed no abnormal rise of the manometer to be noticed. 

 It needs no argument, that not only with a view to oxygen-supply 

 and measuremeni, but also for other leasons, the CO, due to re- 

 spiration, should be directly removed. With a COj-accumulation in 

 the vessel, a volumetric determination of the vanished quantity of 

 Oj is no more i)Ossible. Besides in this case part of the plants gets 

 into an atmosphere full of CO, and deficiency of 0, will soon cause 

 intramolecular respiration. 



It seems to me, that in the respiratoiy apparatus after the model 

 given by Pfeffeh and Detmer and used e.g. by Kuyper, little or no 

 attention has been paid to the error which may be committed, 

 when in a respirator}' vessel as described in this paper, no perfect 

 ventilalion is provided for. 



The loose bottom h is provided with a marginal groove, containing 

 a rubber-ring. The handle be bears in its middle a screw .?, which, 

 when turned up, presses on re and by doing so presses the lower 

 edge of the vessel tightly in the groove with rubber-ring. 



In the cover of the vessel is, besides the aperture o to admit 

 oxygen, also a pierced rubber-cork through which a thermometer 

 th passes. 



6'. Fig. 4 gives a ie|)iesentation of the drying-tubes and the 



