GEOTROPISM 427 



is meant, as previously explained, the angle which direc- 

 tion of stimulus makes with the responding surface. 



4. We have finally to investigate, whether the assump- 

 tion of opposite irritabilities of the root and the shoot is 

 at all justifiable. If not, we have to find the true explan- 

 ation of the opposite curvatures exhibited by the two types 

 of organs. 



Of these the first three are inter-related. They will, 

 however, be investigated separately ; and each by more than 

 one method of inquiry. The results will be found to be 

 in complete harmony with each other. 



I propose in this and in the following chapters to 

 carry out the investigations sketched above, employing two 

 independent methods of enquiry, namely, of mechanical 

 and of electrical response. I shall first describe the auto- 

 matic method I have been able to devise, for an accurate 

 and magnified record of geotropic movement and its time 

 relations. 



THE GEOTROPIC RECORDER. 



The recorder shown in figure 157 is very convenient 

 for study of geotropic movement. The apparatus is four- 

 sided and it is thus possible to obtain four simultaneous 

 records with different specimens under identical conditions. 

 The I'ecording levers are free from contact with the record- 

 ing surface. By an appropriate clock-work mechanism, 

 the levers are pressed for a fraction of a second against 

 the recording surfaces. The successive dots in the 

 record may, according to different requirements, be 

 at intervals varying from 5 to 20 seconds. The 

 records therefore not only give the characteristic curves of 

 geotropic movements of different plants, but also their time 



ations. For high magnification, I employ an Oscillating 



