THE LEAF CONSIDERED AS AN ELECTRIC ORGAN 255 



excitability of the two is liable to undergo reversal, under 

 the changing conditions of age, season, and fatigue induced 

 by previous stimulation. In the leaf of Pterospermum, 

 however, which I have here taken as the type corresponding 

 with Torpedo, the normal differential excitability is generally 

 very persistent. Here the excitability of the posterior 

 surface, which is leathery, is slight, and practically negligible. 

 But the anterior surface, with its rich and prominent venation, 

 is highly excitable. The excitatory discharge of such a leaf 

 is thus from the anterior to the posterior. I give in fig. 162 

 a series of its responses to equi-alternating electric shocks. 

 It will be seen that these are 

 very uniform, and exhibit 

 practically no signs of fatigue. 

 We have thus found a 

 vegetable organ whose re- 

 sponses are exactly parallel 

 to those of a single plate of 

 the electrical organ of Torpedo 

 and its type. We shall next 

 study the responsive pecu- FlG - l6 T 2 ' f Se f ries f Res P onses 



* by Leaf of Pterospermum sitben- 



liarities of the vegetable organ folium to Stimulus of Equi-altemat- 



, j ing Electrical Shocks at Intervals ot 



wnose responses correspond x M inute 

 with those of the organ of 



Malepterurus. It has been mentioned that the posterior surface 

 of each single element of this electrical organ is regarded as 

 consisting of a glandular, rather than a muscular, modification. 

 Among corresponding leaf-organs, then, the carpellary leal 

 of Dillenia indica might, as we also saw, be taken as the 

 type, its posterior surface being glandular. Or the analogy 

 will be still more perfect if we take as the vegetal type the 

 pitcher of Nepenthe. Here the internal or posterior surface 

 is richly provided with glands. The next point to be deter- 

 mined is whether, in these cases also, on excitation the 

 responsive current is from the posterior surface to the anterior, 

 as in the electrical element of Malepterurus. " And on sub- 

 jecting them to equi-alternating electrical shocks, I found 



