159 



hydrogen, showed no after-effect, we may not conclude. 

 that no perception is possible in an atmosphère free from 

 oxygen, or that the ..disposition to curve" cannot arise. 

 Czapek also repeated Correns' experiments in hydrogen. 

 but found that a sojourn of more than 6 hours was 

 harmful. Now the method which he adopted, was based 

 on an investigation by Chudiakow ^) who had found that 

 in an oxygen-free atmosphère seedhngs perish the sooner, 

 the higher the température is. Czapek experimented with 

 lupin seedlings which he placed vertically in the receiver 

 of an air-pump. He exhausted to 1 m. m. of mercury and 

 then admitted a current of hydrogen. He repeated thèse 

 two opérations 6 to 8 times. Then the vessel was placed 

 horizontally in powdered ice. In this way the roots remained 

 24 hours at a température of from 0° to 2° C. After 

 this interval the roots looked perfectly normal. They were 

 then placed on the clinostat and after 4 — 6 hours a 

 distinct geotropic after-effect had made its appearance. 

 Although in the vessel longitudinal growth did not take 

 place, geotropic induction is evidently still possible, 

 provided that care is taken to exclude harmful factors. 



In 1912 Arpâd Paâl-) published a paper, which 

 likewise only dealt with geotropism. The method which 

 he adopted for studying the influence of reduced pressure 

 on the geotropic-stimulation process, consisted in the 

 détermination of reaction- and presentation-times. The 

 radicles of Phaeseolas vulgaris, with which he worked, 

 were placed horizontally under the bell-jar of an air-pump, 

 and he observed at différent pressures of air. how long it 

 required before the majority of the roots showed a cur- 

 vature. The resuit of thèse experiments was that the 



') N. V. Chudiakow. Beitrâge zur Kenntniss der intramolekularen 

 Athmung. Landwirtsch. Jahrb. 1894, Bd. 23, p. 333. 



-) Arpâd Paâl. Analyse des geotropischen Reizvorgangs mittels 

 Luftverdùnnung . Jahrb. f. wisschensch. Bot. 1912, Bd. L, p. 1. 



