ir»2 SENSITIVENESS OF TUE APEX Chap. HI. 



been longer observed, the tip no doubt would have 

 been foand again curved down, and it would have 

 formed a loop as in the following case. The twelfth 

 radicle after 6 h. was slightly curved downwards ; but 

 when looked at again after 21 h., this curvature had 

 disappeared and the apex pointed upwards ; after 30 h. 

 the radicle formed a hook, as shown at A (Fig. 67) ; 

 which hook after 45 h. was converted into a loop (B). 

 The thirteenth radicle after 6 h. was slightly curved 

 downwards, but within 21 h. had curved considerably 

 up, and then down again at an angle of 45° beneath 

 the horizon, afterwards becoming perpendicular. In 

 these three last cases geotropism and the irritation 

 caused by the attached squares alternately prevailed 

 in a highly remarkable manner ; geotropism being 

 ultimately victorious. 



Similar experiments were not always quite so suc- 

 cessful as in the above cases. Thus 6 radicles, horizon- 

 tally extended with attached squares, were tried on 

 June 8th at a proper temperature, and after 7 h. 30 m. 

 none were in the least curved upwards and none were 

 distinctly geotropic ; whereas of 6 radicles without any 

 attached squares, which served as standards of com- 

 parison or controls, 3 became slightly and 3 almost 

 rectangularly geotropic within the 7 h. 80 m. ; but 

 after 23 h. the two lots were equally geotropic. On 

 July 10th another trial was made with 6 horizontally 

 extended radicles, with squares attached in the same 

 manner beneath their tips ; and after 7 h. 30 m., 4 were 

 slightly geotropic, 1 remained horizontal, and 1 was 

 curved upwards in opposition to gravity or geotropism. 

 This latter radicle after 48 h. formed a loop, like that 

 at B (Fig. 67). 



An analogous trial was now made, but instead of 

 attaching squares of card to the lower sides of the 



