— 135 — 



strictly central; P is a metal plate, the plane of which is at night 

 angles to that of D; P is moveable and can be fixed so that its 

 inner edge is in line with the axis oiB^). A Sorghum seedh'ng (S) 

 is fixed by its cotyledon to F by means of gypsum. When the 

 machine is set in motion it is evident that the hypocotyl and the 

 cotyledon being on different sides of the axis of rotation the 

 direction of the resulting curvature will depend on where the 

 gravitational Stimulus arises. If geo-perception resides exclusively 

 in the hypocotyl it is clear that the curvature will be in direction H— 



Fig. 7. 



towards the axis. But if geo-perception is confined to the cotyledon 

 the reverse will happen by the transmission of a Stimulus from 

 the cotyledon. 



This is the result we have obtained, namely the curvature of 

 the hypocotyl away from the centre. Our experiments do not prove 

 that no geo-perception exists in the hypocotyl, but they do prove 

 that if such sensitiveness exists, it is overcome by the Stimulus 

 originating in the cotyledon. 



') In practice the plate P is placed so that the cotyledon and not the 

 plate is over the point B. The arrangement by which P is fixed in the desired 

 Position is not shown. 



