153 



Kraus ^) in an appendix to his paper on the distribution 

 of water in plants, deals with the behaviour of geotropi- 

 cally irritable organs in a COo- or H-atmosphere. 



He used for his experiments flowering shoots of 

 Taraxacum, Ranunculus, Anthriscus silvestris etc., which 

 he placed horizontally in a vessel, through which a con- 

 stant current of COo or H was passed. Six hours later 

 no trace of érection was visible, but, if the stems were 

 afterwards brought into the air, they were, after 5 hours, 

 curved upwards. Irritability is therefore lost in an oxygen- 

 free atmosphère, but returns in ordinary air, a proof 

 therefore, that the plants merely pass into a condition of 

 rigor (..asphyxie", ..starre"). 



An entirely new method of studying the influence of 

 oxygen on geotropic processes was adopted by Wort- 

 m a n n "). He used seediings of Phaseolus multiflorus, 

 Helianthus annuus and Lepidium sativum and placed them 

 under the bell-jar of an airpump. In a partial vacuum, a 

 slight curvature, which had previously been induced in 

 ordinary air, was continued, but only for a short time 

 and no further continuation of the curvature could be 

 obtained even after admitting atmospheric air. But if air 

 was admitted while a slight curvature was still taking 

 place, the movement again became more vigorous and 

 could even proceed as far as in ordinary air. He remarks, 

 that the same phenomenon had already been observed by 

 Wieler^) for growth; since geotropism is a growth 



^) G. Kraus. Ueber die Wasservertheilung in der Pflanze IV. Die 

 Aciditât des Zellsaftcs. Abhandlungen der Naturforschenden Ges. zu 

 Halle, Bd. XVI, 1884, p. 199. 



^) J. Wortmann. Studien ûber geotropische Nachwirkungserschei- 

 nungen. Bot. Zeitg. 1884, p. 705. 



■^i A. Wieler. Die Beeinflussung des Wachsens durch verminderte 

 Partiârpressung des Sauerstoffs. Unters. aus dem Bot. Inst. zu Tùbingen 

 I. 1883, p. 189. 



