— 129 — 



The Steps by which the curvature is produced must be small 

 so that the process of bending should take at least 5 minutes. It is 

 best not to attempt a bend through quite QO", for even with smaller 

 amounts of curvature the cotyledon often breaks at the bend. The 

 preparation is then floated on water for 5 minutes or so to allow 

 turgescence to be regained. Any gravitational Stimulus produced in 

 this way is at right angles to the experimental plane of curvature. 



The specimens are then placed, the plane in which the cotyledon 

 is bent being vertical, under a bell jar in the moist atmosphere of 

 a dark incubator kept at 24—25". 



i 



i 



Ficr. 4. Position 1. 



Fis. 5. Position 2. 



The arrow C shows the direction of curvature to be expected if 

 the Stimulus originates in the cotyledon: // shows the direction in which the 

 hypocoty! would bend if it were independeiitly geotropic. 



Two positions were in the first instance employed, as shown 

 in the figures. In both cases it must be understood that the plants 

 are supported by the cotyledons, as in my experiments of 18Q4. 



Assuming for the moment thatgeo-perception resides in the coty- 

 ledon, we may further assume that the curvature will obey the Stimulus 

 arising in the apical three-quarters of the cotyledon rather than the 

 Stimulus originating in the basal quarter. Therefore on this as- 

 sumption we should expect in Position 1 (Fig. 4) that the hypocotyl 

 would curve downwards in direction C. This is what was found 

 to occur almost without exception. Whereas if the hypocotyl were 

 independently geo-perceptive, the curvature would obviously be 

 upwards in the direction //. 



Wiesnei-Festschiift 9 



