RESPONSIVE CURVATURES— NEGATIVE GEOTROPISM 497 



describe a typical experiment showing the excitatory effect 

 of pressure in inducing responsive curvature. That unilateral 

 pressure or contact does induce curvature is known in the 

 case of tendrils ; but in the present experiment I shall show 

 that this responsive reaction is not peculiar to tendrils alone, 

 but is exhibited by all organs alike. I was also desirous of 

 making the action on my experimental specimens in every 

 way parallel to that of gravitationally excited tissue in which 

 the statolithic particles exert 

 their weight on a particular 

 side of the responsive organ. 



I took a specimen of 

 Crinum Lily and mounted it 

 vertically. I next took a thin 

 strip of india-rubber, the inner 

 surface of which was studded 

 with iron particles, adhering 

 by means of shellac varnish. 

 This was adjusted laterally, 

 on one side of its zone of 

 growth, so as almost, but not 

 quite, to touch the specimen. 

 On the opposite side was 

 placed an electro-magnet, 

 which when excited attracted 

 I the strip to which the iron 

 particles adhered, and thus 



produced a unilateral pressure on the specimen, the magnetic 

 particles functioning as so many statoliths (fig. 205). A 

 recording microscope, which will be fully described in a later 

 chapter, was now focussed on the index, I, attached to the 

 specimen. 



Before the application of pressure, the quiescent condition 

 of the specimen had been ascertained by noting the stationary 

 position of the index in the field of view of the microscope. 

 On now applying unilateral pressure by exciting the magnet, 

 we might expect to obtain two different effects. The first of 



K K 



Fig. 205. - Diagrammatic Repre- 

 sentation of Experiment showing 

 Curvature Induced by Unilateral 

 Pressure Exerted by Particles 



F, flower-bud of Crinum ; s, india- 

 rubber strip studded with iron 

 particles attracted by electro- 

 magnet, M, causing unilateral 

 pressure on growing region ; 1, 

 index attached to flower. 



