FUNCTION.] CYCLOSIS IS AN ERROR. 343 



while the connexion between the leaf under examination and 

 the rest of the plant was unbroken, a current could generally 

 be perceived which lasted for about half a minute and then 

 gradually ceased ; he satisfied himself that this was produced 

 by the torsion and compression of the vessels of the neigh- 

 bouring parts. When the petiole was cut across, a very rapid 

 current took place towards the wound, which continued until 

 the coagulation of the extravasated latex closed the wounded 

 vessels. On cutting a little further up, the current was set 

 up again. In the leaves of Tragopogon mutabilis, where the 

 principal nerves take a rectilinear direction, the current could 

 be made to flow from the summit to the base, or from the 

 base to the summit of the leaf, according as the apex or the 

 petiole of the leaf was cut off. The slightest pressure, also, 

 affected the direction of the current." 



