-- 131 — 



5 bent in direction //and only one in direction C. Eight experimenis 

 in Position 1 gave C curvatures which in this case is in direction 

 of the traumatic effect. 



Seven experiments were made vvith glass tubes in position 3 

 (Fig. 6). 



Tiiis Position is of no special importance since tiie Stimulus 

 arising in the hypocotyl produces the same curvature (H) as that 

 originating in the cotyledon (C;. The experiments were undertaken 

 to make sure that the w eight of the hypocotyl and seed do no- 

 determine the direction of curvature with plants in position 1. 

 Out of the 7 plants, (j curved up (in direction C and 77), the seventh 

 downwards. 



The experiments are also worth giving for another reason; 

 if the average curvature had not been markedly in direction C, H, 

 the result would have been only explicable as the result of a 

 traumatic effect acting in the opposite direction to the bend in the 

 cotyledon and strong enough to overcome the geotropic effect. 



To test the theory that forcible curvature of the cotyledon 

 produces a traumatic curve in the hypocotyl a few experiments 

 were made in which the cotyledons were forced into bent tubes, 

 and then kept on a klinostat in the dark for 5 to 6 hours, Eighteen 

 seedlings were so treated, in all of which the hypocotyl curved in 

 the direction of the bend in the cotyledon. The amount of curvature 

 varied from 15" to 70" and gave an average of 3Q". 



In conclusion of this part of the inquiry it must be especially 

 noted that though the occurrence of a traumatic effect renders the 

 experiments unsatisfactory, yet the results seem only explicable on 

 the assumption that geo-perception resides in the cotyledon — or 

 at least that the cotyledonary Stimulus is stronger than that arising 

 in the hypocotyl. For if the reverse were the case, if the master- 

 stimulus had resided in the hypocotyl, Position 2 should have given a 

 uniform curvature in direction H, since the geotropic and traumatic 

 results would have been superposed. Whereas Position 1 should 

 have given irregulär results because geotropism would have been 

 opposed by the traumatic effect. 



III. Beut cotyledons heliotropioally stinmlated. 



In Order to test the geotropic results a similar set of ex- 

 periments were made with light as the Stimulus. 



9* 



