13 



Thus Haberlandt published in 1902 and in 1903 

 experiments in support of the statolith-theory ; he used 

 plants which were grown out of doors duiing winter and 

 afterwards transferred to a température of about 20° C, 

 Thèse experiments led Haberlandt to the conclusion 

 that négative! y geotropic stems, freed from starch by a 

 prolonged sojourn at a température of a few degrees above 

 0° C, are net able to curve geotropically before the starch 

 is regenerated. 



Similar experiments were made in the same year by 

 Francis Darwin, with much the same results. Darwin 

 kept his objects of experiment from 6 to 26 hours at 

 33° C. — 88° C. and by means of thèse high températures 

 he too was able to eliminate starch more or less completely. 

 Hère also this élimination was accompanied by a more or 

 less complète disappearance of the faculty for geotropic 

 reaction. 



Control-experiments, in which the phototropic reaction 

 of plants thus treated was investigated, showed that the 

 faculty for phototropic reaction decreased at nearly the 

 same rate, so that Darwin did not regard thèse experiments 

 as proving the validity of the statolith-theory. 



Evidently of quite a différent nature are the cases, 

 principally investigated by Vôc h tin g (1898) and Lidforss 

 (1903), for which Vôchting h as proposed the name 

 psychroclinic reactions. Both investigators found that a 

 change of température causes a change of disposition 

 with regard to geotropism, especially in spring-plants. 



Several plants, diageotropic at low température, become 

 negatively geotropic when the température rises, while 

 conversely they change again from négative geotropism 

 to dia-geotropism when the température falls. 



As thèse phenomena are insufficiently known and do 

 not bear directly on the présent investigation, 1 hâve not 



