- 137 — 



will be 2-8X0'707 g= 1"Q7 7; the value of the centrifugal force 

 in Table III is calculated in this way. 



Table III. 



Angle 

 to axis 



Curve 



Exposure '^^"7'^"- 

 hrs. gal to^" 



Exp. 7 

 Exp. S 

 Exp. 12 

 Exp. 15 

 Exp 16 

 Exp. 17 

 Exp. 19 

 Exp. 2Q 

 Exp. 21 



Mar. 5, 

 Mar. 8, 

 Mar. 13, 

 Apr. 19, 

 Apr. 20, 

 Apr. 22, 

 Apr. 24, 

 Apr. 26, 

 Apr. 29, 



1907 

 1907 

 1907 

 1907 

 1907 

 1907 

 1907 

 1907 

 1907 



4J0 



45 

 45 

 40 



? 



45 

 43 

 50 

 44 



5 



l^'3 



5 



4 



7 

 6 



1-2 

 M 

 M 

 11 



0-8 

 1-8 

 1-6 

 1-7 



Thus in all the experimenls the curvature was away from the 

 centre, i. e., in the direction to be expected if geo-perception resides 

 in the cotyledon. 



There are two other possible explanations of the fact. (1 ) That 

 the hypocotyl is pros — instead of apogeotropic; this may be dismissed 

 for want of other evidence. (2) That the curvature from the centre 

 is not a growth-curvature but a physical bending, the direct result 

 of the centrifugal force. This theory would be easily disproved if 

 the seedlings had been more actively geotropic when they might 

 have shown the curling up into spirals, or might at any rate have 

 curved well beyond the plane parallel to the disc D. This, however, 

 only occurred in two cases, neither of which were quite satis- 

 factory. 



There is, however, a simple way of showing that the result 

 is not due to ductility, namely, the repetition of the ordinary Knight's 

 experiment with Sorghum. The plants were fixed in tubes or by 

 means of plaster of Paris so that the whole plant (which was 

 oblique to the axis of rotation) was from T5 to 3 cm from the 

 axis. Thus whether the cotyledon or hypocotyl is the seat of geo- 

 perception the hypocotyl ought to curve towards the centre. 



