134 



SENSITIVENESS OF THE APEX Chap. IH. 



always fixed to the cork-lids, for the convenience of 

 manipulation, with the edge from which the radicle 

 and plumule protrudes, outwards ; and it must be 

 remembered that owing to what we have called Sachs' 

 curvature, the radicles, instead of growing perpendi- 

 cularly downwards, often bend somewhat, even as much 



Vioia faba : A, radicle beginning to bend from the attached little square 

 of card ; B, bent at a rectangle ; C, bent into a circle or loop, with the 

 tip beginning to bend downwards through the action of geotropism. 



as about 45° inwards, or under the suspended bean. 

 Therefore when a square of card was fixed to the apex 

 in front, the bowing induced by it coincided with Sachs' 

 curvature, and could be distinguished from it only by 

 being more strongly pronounced or by occurring more 

 quickly. To avoid this source of doubt, the squares 



