lf>2 SENSITIVENESS OF THE APEX CHAP. Ml. 



been longer observed, the tip no doubt would have 

 been found 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. 30 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 

 slight ly 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 



