412 Prof. Burdon- Sanderson and Mr. F. J. M. Page [Dec. 14, 



very cautiously, with the aid of a camel-hair pencil, it can be pre- 

 dicted with certainty that no visible effect will be produced ; and a 

 similar gentle contact may be repeated several times before the leaf 

 begins to answer to the irritation by any movement. Sooner or later, 



