

37 



was general, with the intention of examining whether the 

 motion would return again when they were immersed in water : 

 he has never found, however, the circulation to be restored, 

 no matter how short a time had elapsed since the stoppage, 

 or how low or high the degree of heat had been, at which 

 the stagnation had taken place. This is a strong argument 

 against the probabihty of a physical cause for the phenomenon. 



" The physical causes assumed to account for the matter had 

 been various, and he would notice a few. 



"Endosmose and exosmose had been considered competent 

 to explain the phenomenon, and he had at one time enter- 

 tained the same notion; but the idea is untenable, for the 

 circulation goes on equally well in water, and in air (until 

 desiccation is produced), in oil, and in a saccharine solu- 

 tion. 



"Others had attempted to account for it on the principle 

 of that epipolic force, which causes two fluids of different 

 densities and miscible materials in contact with each other, to 

 be in a constant state of rotation until they are entirely amalga- 

 mated. This, however, assumes the existence of two fluids in 

 the plant ; whereas, we have every reason to believe that one 

 only, i. e., that within the cell, is necessary to the production 

 of the circulation. Even if the existence of the two neces- 

 sary fluids be granted, we have every reason to beheve that 

 their action upon each other would be uniform, not fitful and 

 irregular, as we have seen the motions of the chlorophyll to 

 be. 



" Electricity has been proved to have no direct agency 

 at all. 



"The author was led to consider that the phenomenon in 

 question is due to vital causes, by the following considera- 

 tions : — 



"That the circulation is fitful and irregular, varying in 

 rapidity at different points (if the same cell. That although 

 if docs not ordinarily exist in the valisncria when growing, vol 



