26 Macfarlane. — Contributions to the History of 



hour into increasing strengths till forty-five per cent, was 

 reached, when it closed. 



Glycerine like strong sugar solution causes contraction 

 and like it in a rather slow manner. Strong solutions of 

 ammonium carbonate and citrate stimulate to closure in 

 from twenty to forty seconds, while dilute sulphuric, hydro- 

 chloric, and nitric acids act in from two to ten seconds. 

 Three minute crystals of solid chromic acid were laid on a leaf 

 and left for a minute without producing movement. They 

 were then wetted by a minute drop of water, when closure 

 occurred after eighteen seconds. A crystal about half as 

 large as a pin's head was then arranged and wetted, when the 

 leaf closed in five seconds. Minute fragments of potash and 

 soda stick were arranged and dissolved, when the leaves 

 operated on closed in from six to thirteen seconds. 



Absolute alcohol, ether and chloroform are all rapid stimu- 

 lants if dropped on in the liquid state, but the vapor acts 

 according to its amount, contracting the leaf slowly but com- 

 pletely if abundant ; contracting it only partially if less so, 

 and rendering it insensible and powerless if the quantity be 

 still less. But of the substances tried corrosive sublimate 

 and one per cent, osmic acid— notably the latter — are the 

 most powerful stimulants, and a leaf responds to their pres- 

 ence in one to three seconds. 



Different substances, therefore, stimulate to very different 

 degrees, and even the same stimulant can cause closure in a 

 time ratio that is proportionate to the strength or concentra- 

 tion of it. These and other substances not mentioned above 

 are exactly comparable in their action to that on muscular 

 tissue. Now, in the case of many of the above agents there 

 was ample time for osmotic action to be set up. But while 

 some set up endosmotic flow, others, such as sugar solution and 

 glycerine, would cause vigorous exosmotic flow. Though we 

 may not be able as yet to explain fully their action on the con- 

 tractile protoplasm, it seems to us that the phenomena here 

 are identical with those of muscular tissue, and that we have to 

 deal in the leaf substance with an organized material iden- 

 tical in its fundamental behavior with muscle, though greatly 

 less sensitive in its response to stimuli. 



