CH. Vll] DECAPITATED ROOTS. 173 



Section B. Curvatures due to injury, contact, etc. 



(204) Decapitation of roots'^. 



Select 10 healthy germinating beans with straight 

 roots growing vertically downwards. From 5 of them cut 

 off 1 mm. measured from the extremity of the root-cap : 

 the amputation must be made by a strictly transverse 

 section, and the amputated point should include part of 

 the growing point. Place the 10 beans horizontally in 

 damp sawdust for 12 to 18 hours at a temperature 

 of 15° — 16° C. and compare the amount of geotropic 

 curvature. 



The result is not quite constant, it may however be 

 safely said that decapitation prevents or greatly diminishes 

 geotropic curvature I 



(205) Decapitation prevents the perception of the stimulus. 

 Place 10 beans horizontally in damp sawdust for 



1^ hours ; the tips {\^ mm.) are now amputated and 

 the roots embedded vertically in damp sawdust. After 

 12 hours the roots, or most of them, will be found to be 

 curved laterally towards the side which was downwards 

 during the period (1^ hr.) during which they were kept 

 horizontal. This shows that amputation does not interfere 

 with the carrying out of an induced curvature, so that the 

 absence of geotropism in exp. 204 must be due to a 

 disturbance of the capability of being stimulated. 



1 Ciesielski, Ahioartskriimmung der Wnrzel Inaug. Dissert. Breslau, 

 1871. Power of Movement, p. 523. 



- A good deal of literature exists on this point and on the facts given 

 in exp. 207. References are to be found in Frank's Lehrbuch der 

 Botanik, i. p. 477. 



