24 Macfarlane. — Contributions to the History of 



Leaf Closure. 



(d) By Chemical Stimuli. 



The consideration of this opens a very wide field, the 

 border of which only we are persuaded has as yet been 

 touched. All who have looked into the subject from Curtis 

 and Canby onwards have noted the great differences in action 

 which different substances possess. But Darwin and Dr. 

 T. A. G. Balfour are the two writers to whom we are indebted 

 for the most extended observations. I have repeated nearly 

 all of their experiments, and have added others which sug- 

 gested themselves as likely to extend the line of work. Gar- 

 diner's suggestive results have also been of use. 



Balfour found that chloroform, chloride of ammonium, 

 carbonate, sulphate, and borate of soda, sulphate of copper, 

 meat, and various nitrogenous food stuffs, also pepper, all 

 caused closure, though he does not state the strength of any 

 of the solutions used. Darwin found that a moderately 

 strong solution of sugar, chloroform, ether and nitrogenous 

 compounds caused closure. Chloride of strontium and sul- 

 phate of iron, however, were without effect, but killed the leaf, 

 according to Balfour ; while according to Darwin hydro- 

 cyanic acid paralyzed two leaves for a time though they 

 continued to remain open. 



Though somewhat arbitrary in method substances will be 

 treated of in the order that they appear to stimulate the leaf. 

 At 9.30 a.m. on a clear day, three minute shreds of roasted 

 meat were wetted and very carefully laid on as many leaves in 

 the axil of a hair with the leaf surface. None of the leaves 

 closed. One of them was then twice touched, when it closed 

 and remained so for eleven days and poured out an abundant 

 secretion. One was slightly closed at 4 p.m., the third remained 

 unaffected. Next day at 9.15 the second leaf had closed, the 

 latter was still open. The former remained shut for eight 

 days, the latter never closed, and its meat particle was finally 

 washed off in watering. Three leaves were chosen at 9 15 

 on another day, and on one a minute shred of meat was 

 placed on the outer end. It showed no change at 5 p.m., but 



