CH. VIIl] TENDRILS. 185 



(231) Tendrils: De Vries' injection experiment^. 



Touch 4 or 5 Bryony tendrils as described in exp. 230, 

 and as soon as they begin clearly to curl, inject them with 

 water under the air-pump: the tendrils need not be 

 weighted or kept in any other way under the surface, but 

 simply thrown into a bottle of water connected with the 

 pump. They will be seen to curl up rapidly into helices 

 of 2 or 3 turns. 



A similar result may generally be obtained by touching 

 tendrils and then placing them in water at 35° C. In this 

 and the injection experiment a few tendrils should be 

 placed in cold water to serve as controls. 



(232) Tendrils: Pfeffer's contact eicperiment. 



Pfeffer^ has shown that only rough bodies which 

 produce discontinuous pressure serve to stimulate tendrils, 

 while perfectly smooth homogeneous bodies are not 

 irritating. 



Melt 2 sheets of Marshall's "Leaf Gelatine" in half a 

 cupful of warm water ^: dip into it while still hot a 

 smooth wooden or glass rod about 3 mm. in diameter. In 

 this way a length of 4 or 5 cm. is coated and must be 

 allowed to cool thoroughly before use. The gelatine- 

 coated rod, which must be kept as free from dust as 

 possible, is now to be employed to touch the tendrils of 



' De Vries, Archives Neerlandaises, xv. 1880, p. 269. 

 ' Untersuchungen aus d. hot. Imtitut Tubingen, i. 1885, p. 483. 

 ' PfefEer uses solutions containing from 5 to 14 per cent, of air-dry 

 gelatine. 



