15 



time also give the figures referring to the reaction time. 

 The time factor as Blackman called it was introduced 

 by vvarming the objects of experiment (coleoptiles of 

 Avena) one or more hours before the induction. 



Besides investigating generally the influence of tempe- 

 ratures between 0° C. and 40° C. on the geotropic process, 

 as judged by the changes in the presentation-time, I hâve 

 especially sought an answer to the three folio wing ques- 

 tions: 1) the validity of van 't Hoff's law; 2) the varia- 

 bility of the optimum in relation to the time factor; 

 3) the occurrence of limiting factors. 



For a further statement of the reasons which led to* 

 the adoption of this method the reader is referred to 

 § 4 — § 1, where everything is discussed in détail. 



CHAPTER I. 



METHOD. 



§ 4. Detailed description of the method. 



At the beginning of the experiment the expérimental 

 plants were placed in the thermostat (of § 6) at the tem- 

 pérature, the influence of which was to be traced, and 

 they were stimulated after they had been in the thermo- 

 stat for oue or more hours. After the stimulation they 

 were brought back to ordinary température (18° C. — 21° C), 

 when the reaction was awaited and was examined by 

 red light at intervais, of 5 minutes. 



The plants were not put on the clinostat during the 

 latent period (between the stimulation and the moment 

 when the reaction becomes visible), since Mrs. R u 1 1 e n — 

 Pekelharing') has shown — and I hâve found this to 



1) R u 1 1 e n— P e k e 1 h a r i n g, 1910, p. 258 and 259. 



