Diotuea Afuscipula, lillis. 27 



1 .1 a 1 Closure. 



(e) By Electrical Stimuli. 



After the elaborate researches of Bunion Sanderson, it is 

 not necessary that we should do more than refer to the fact 

 that closure follows application of this form of energy. We 

 have not yet determined accurately whether two sharp and 

 distinct stimuli are needed or whether one suffices, but there- 

 are grounds for believing the former to be true. In all ca 

 the electrical terminals were delicately applied to the lower 

 external parts of the leaf halves, after moistening of the sur- 

 faces, and closure has invariably been effected. It seems 

 difficult to determine, from Sanderson's account, whether he, 

 in all cases, inserted the terminals into the leaf substance, or 

 only in connection with certain experiments, but closure by 

 electrical stimulus from the external surface is another proof 

 of the general sensitiveness of the leaf. 



II. Leaf Structure. 



Oudemans, T. A. G. Balfour, Darwin, De Candolle, Frau- 

 stadt, Kurtz, Batalin, Sanderson, Gardiner and Goebel have 

 all described the histology of the leaf, but it is curious, indeed, 

 that the descriptions and figures of the great centres of irri- 

 tation — the hairs — are of the most general and imperfect 

 nature. Oudemans, De Candolle, Fraustadt and Kurtz have 

 given more attention to the general histology and develop- 

 ment of the leaf. The two last are at variance as to the 

 stomata on the marginal bristles, the former stating that 

 they are present, the latter that they are absent. They are 

 present in small numbers along the lower or external faces, 

 but absent on the internal or upper, as might be expected. 

 The brown stellate hairs referred to and figured by Oudemans, 

 and noted by his successors, occur on the upper and lower 

 surfaces of the expanded petiole, but only on the under 

 surface of the blade. We would point out here that their 

 structure and development essentially agree with those of 

 the secreting glands on the upper leaf lamina. They fur- 

 ther exhibit considerable variability in the mature state, and 



