vi ELECTROMOTIVE ACTION IN VEGETABLE CELLS 7 



consists of two distinct lobes, which, like the wings of the petiole, 

 are attached to the highly convex mid-rib. At its margin the 

 leaf is prolonged at tolerably regular intervals into bristle-like 

 processes, which hook together alternately when the lobes are 

 folded up. On the surface of each lobe are three small hairs, one 



FIG. 139. 



near the mid-rib, the other two somewhat external to it, and 

 these are essentially the seat of excitability. The inner surface 

 of the leaf is further provided with a number of small discoid 

 glands. The wings of the petiole consist of a soft unstable 

 tissue, while the lobes are lumpy, sappy, and highly resistant. 

 Lateral veins run out at approximately equal distances from the 

 fibro-vascular bundle which passes up the centre of the mid- 

 rib, and form an elegant system of arches at the margin of the 



