CH. VIl] DECAPITATED ROOTS. 159 



while the vertical piece ends in a loop of cotton by 

 which it is attached to the shoot. By twisting the loop 

 it is easy to make the foil press lightly against the 

 smoked paper of a revolving drum ; the T piece being 

 light (about 02 gram) it does not iaterfere with the 

 geotropic action. In a typical experiment of this sort the 

 primary geotropic rise lasted 4 hours, the after effect 

 2 hours. Then came 2 hours in which the index was 

 stationary; finally it rose once more, beginning very 

 slowly. 



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



(204) Decapitation ofroots^. 



Select 10 healthy germinating beans with straight 

 roots growing vertically downwards. From 5 of them cut 

 oif 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 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 diminishes or quite prevents 

 geotropic curvature". 



' Ciesielsti, Abwartskrummung de.r Wursel. Inaug. Dissert. Breslan, 

 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. 



