analogous to the Irritability of Animals. 165 



subject, and to perform very numerous experiments, with a 

 view to learn its peculiar nature and effects. It will be my 

 business in the following pages to state, as succinctly as pos- 

 sible, some of the results of my inquiries. 



To the phaenomenon above mentioned, I have hitherto ap- 

 plied the term divergence, under which appellation I shall 

 here continue to speak of it. But, as the evidence which 

 1 am about to adduce has convinced me of the analogy, if not 

 the identity, of this property with what physiologists call irri- 

 tability'^^ I shall in future venture to consider them as similar 

 principles, and substitute the word irritability for that of di- 

 vergence. 



The experiments which follow will afford a sufficient illus- 

 tration of the phaenomena of divergence. 



Exp. 1. A portion of the stem of a White Dead-Nettie 

 (Lamium album), was divided at one extremity with a lancet, 

 the division being carried to the length of H inch. The seg- 

 ments instantly separated from each other one inch, which 

 gradually increased to If inch. The sketch, fig. I. will serve 

 to show the appearances which presented themselves, a a be- 

 ing the stem previously to, bb the same after division, cc the 

 divided segments in a state of divergence. 



Fig. 1. 



Exp. 2. A slender spray of Yellow Jessamine was divided 

 down the middle. The two segments instantly separated 

 from each other, and remained so when the spray was held 

 in an inverted position; thus showing that the effect did not 

 depend on the weakened segments bending outwards from 



* See System of Physiology, by J. Bostock, M.D., vol. i. p. 160. 



