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JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



The last reading indicates a sudden considerable increase in 

 rate, much greater than was usually the case when the air was 

 changed. 



The chief point to notice is the sudden depression on the 

 entry of the sulphurous acid — a depression which was aggra- 

 vated when additional acid was admitted. 



I was also able to demonstrate that dilute sulphurous acid 

 causes a slight, but by no means complete, closure of the pre- 

 viously widely distended stomates of Ccntropogon when it is led 

 over the leaf in a special " gas-chamber " placed on the stage of 

 the microscope. 



Experiments upon the effect of S0 2 upon respiration are not 

 sufficiently advanced to report upon. An account of them is 

 reserved for a future report. 



On the Action of Pyridine and of Allied Bodies. 



When I inquired of my friend Dr. Bailey, who has been good 

 enough to conduct the analyses of the Chelsea and Kew fog- 

 deposits, as to what might be the more important substances 

 included in the tarry matters of these residues, he replied that 

 41 to a considerable extent some form of pyridine" was present. I 

 have consequently experimented with pyridine, and with a num- 

 ber of allied bodies (for which I am much indebted to Dr. Norman 

 Collie, of University College), with the object of ascertaining 

 whether they exert any hurtful action upon the living tissues of 

 plants. 



Pyridine being extremely volatile, is readily applied as a 

 vapour. My procedure was to place a few drops upon a filter- 

 paper, and to suspend this in the bell-glass in which the shoots 

 for experimentation were placed. With the smaller bell-glasses 

 (under ff cubic foot capacity) I found that a single drop sufficed 

 to produce a marked effect ; whilst with the larger size (about 0 

 cubic feet capacity) two or three drops were ample. A consider- 

 able number of plants were experimented upon with very uniform 

 results. If a shoot of Bouvardia be treated in the way described, 

 a limpness of the leaves is observable within an hour or an hour 

 and a half of the commencement of the exposure. This limpness 

 is first apparent at the margins and apices of the leaves, the area 

 affected gradually spreading to the whole leaf. The only change 



