MOVEMENTS OF IRRITATIOX. 



447 



We now fix on one side, by means of shellac or otherwise, a piece 

 of cork. To this is attached by means of a long pin a seedling of 

 ViciaFabaor Phaseolus 

 with a root a few cen- 

 timetres in length, in 

 such a way that the 

 terminal part of its 

 root rests horizontally 

 on the mercury. After 

 pouring some water 

 on to the surface of 



FIG. 145. Seedling of Vicia Faba, \vhose root is 

 forcing its way into mercury. (After Sachs.) 



the mercury we cover the apparatus with a bell-glass and let it 

 stand. After some time (perhaps twenty-four hours), apart from 

 secondary phenomena, it can be made out that the root-end has 

 forced itself into the mercury. The geotropically curved root 

 overcomes the resistance presented by the mercury, and grows 

 vertically downwards into it (see Fig. 145). 



It can also be demonstrated by means of the apparatus depicted 

 in Fig. 146 that roots execute their downward geotropic cur- 

 vatures with great force. On the board B stands the metal 

 pillar 8. The metal bar St is movable on 8 ; it is also 



Si 



FIG. 146. Apparatus for demonstrating that roots executing 

 geotropic curvatures can do work. 



capable of movement in a horizontal direction from right to left. 

 To fix it in position there are screws. At one end St carries the 

 rod St*, movable upwards and downwards. This supports the 



