35 



slight exposure to cold produced a complete stagnation, 

 which went off again on the application of a moderate heat. 

 These considerations induced the author to helieve, that 

 the phenomenon was altogether dependent upon physical 

 causes (prohahly exosmosis). To test this he introduced a 

 small quantity of a weak solution of alcohol into the water 

 in which a cut portion of the plant was confined, and on 

 watching the effects under the microscope, discovered that 

 the circulation was arrested in every cell, as soon as there 

 had heen sufficient time for the spirit to act ; each glohule 

 of Chlorophyll seemed to he firmly adherent to the side of 

 the cell, and was partially flattened, as if an attempt at 

 exosmose had taken place. A fresh specimen was then 

 introduced, and a small quantity of syrup used instead of 

 alcohol : after a while, each cell was found to he partially 

 filled with the solution, which had accumulated in the part 

 most distant from the surface. Although the globules were 

 thus curtailed in the space they had to move in, their circu- 

 lation continued for some time ; it was, however, stopped at 

 last, prohahly from the increased viscosity of the original 

 fluid contents of the cell. 



Another presumptive proof of the influence of exosmosis, 

 was the appearance of the nucleus of the cell after the 

 circulation had ceased naturally. This is originally a large 

 oval transparent hody which travels with the globules round 

 the cell, frequently turning round upon its own axis at each 

 corner. That part of it in contact with the side is usually 

 flattened more or less; at first it does not appear to have 

 any peculiar adhesive qualities, but as the circulation gets 

 feebler, it is seen to attach to itself the green globules one 

 after another, until the whole are incorporated into one mass, 

 which adheres to the side of the cell. 



The curious and interesting movements of the Minosa 

 Pudica (or sensitive plant), the Hedysarum Gyrans and 

 others, were then adverted to. Most of these motions, he 



