CH. VIl] INJURY. 161 



gravitation-stimulus is restored they curve downwards. 

 Fig. 30' shows this state of things, L indicates the side of 

 the seedling which was downwards while the root was 

 horizontally extended, AB shows the strong induced 

 curvature, BG the geotropic curvature occurring after 

 regeneration of the root-cap. 



(207) Curvature induced by contact, injury &c? 



If a bean-root is amputated by an oblique cut so that 

 the growing point is laterally injured, the root curves 

 away from the injured side. The cut should be made 

 with a razor, the beans should be then pinned to the lid 

 of a jar and may be grown either in damp air or with the 

 tips in water. It is important that the temperature 

 should not exceed 16° C. 



A similar curvature may be produced by contact. 

 Minute squares (1*5 mm. x 1"5) of cardboard or of very 

 fine sand-paper (which adheres well) are to be fixed to the 

 tips of bean-roots by thick shellac varnish which sets hard 

 quickly. It is important that the squares of card should 

 be attached to the slope of the root apex, and that they 

 should be either on the right or left of the root tip : if they 

 are on the anterior or posterior face of the root, the 

 resulting curvature will be in the plane of the cotyledons 

 and therefore liable to be interfered with by Sachs' 

 curvature which occurs in the same plane. The side 

 on which the card must be placed will be understood from 



1 Power of Movement, fig. 195, p. 527. 



2 Power of Movement, Chap. in. 



D. A. 11 



