174 DECAPITATED ROOTS. [CH. VII 



(205 A) Pfeffer's experiment. 



The final proof that the root-tip alone is sensitive to 

 the gravitation-stimulus has been given by Pfeffer 1 and 

 by his pupil Czapek 2 : the following instructions are taken 

 from their publications. 



As material, the authors recommend Vicia faba and 

 Lupinus, the latter being more sensitive but also more 

 liable to accidental curvatures. A number of glass tubes 

 in which the roots are to be constrained to grow into a 

 desired form must first be prepared. These are L-shaped, 

 one end being closed, the other open ; their total length 

 is 3 mm. and they weigh about 30 milligrams. Czapek 

 says they are easily made by drawing out a thick- 

 walled tube of soft glass in the blowpipe : the rect- 

 angular bend is got by heating a very short region, care 

 being taken to avoid narrowing the bore by a sudden 

 bend. One limb of the tube is closed in the blowpipe at 

 1*5 mm. from the angle, the other limb broken across at 

 the same length, the edges being afterwards rounded in 

 the flame. The bore of the tube must depend on the size 

 of the roots used, and it is important that the tubes should 

 not fit too closely. 



The caps are cemented to a sheet of cork, to which 

 seedling beans, lupins, &c. are pinned in such a way that the 

 tip of each root is contained in the open limb of a L tube, 

 and reaches nearly to the bending place. The cork plate 



1 British Association, August, 1894, Annals of Botany , vin. Sept. 1894, 

 p. 317. 



2 Jahrb. f. wiss. Bot., xxvn. 1895, p. 243: also Band xxxv., 1900, 

 p. 313. 



