6 



JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



1 1 /?. When we have a severe fog at Kew a greasy deposit 

 is left on the glass which is by no means easy to remove 

 without considerable friction. Fortunately, last year a fall 

 of sleety snow did the scrubbing for us ; mere rain will not 

 remove it. This deposit is in great part carbon cemented 

 with some of the less volatile hydrocarbons. 



" y. The toxic influence in this connection may be due 

 to the presence of more volatile bodies. This is a part of 

 the inquiry where novel and interesting results may 

 particularly be looked for. 

 " I think our first task must be to ascertain something a little 

 more definite about the actual constitution of fog. I rather 

 lament the disposition of chemists to assume that they know all 

 about it. I don't agree that they do." 



In view of the uncertainty existing as to the action of the 

 various substances present in a foggy atmosphere upon vegetation, 

 and the complication introduced by the fact that these noisome fogs 

 are also accompanied by a not inconsiderable reduction of light, I 

 have made it my business to trace the effects of a number of 

 fog impurities upon stove plants under varying conditions. I 

 know very well that the effects on vegetation of many of the 

 noxious vapours present in coal smoke, or liable to escape from 

 alkali works, have been studied from time to time by many 

 persons both in this country and upon the Continent. But, so 

 far as I have been able to ascertain by consulting the literature, 

 neither the microscope nor the spectroscope has been hitherto 

 applied to investigation in this field. I mean by the experts 

 who have given evidence before Royal Commissions and the like. 

 Further, in a very essential point, the circumstances of our 

 inquiry differ from those which have preceded it. This is the 

 reduction of light consequent on the suspended matter in the 

 air. No inquiry can probe this difficult question, unless the 

 action upon plants of prolonged gloom or darkness be held in 

 view. But more of this anon. 



Of the known impurities of urban fog I have traced the 

 action of the following, which, for one reason or another, I have 

 suspected to be inimical to plant life. These are : Sulphuric 

 acid, sulphurous acid, hydrochloric acid, ammonia, metallic 

 iron, ferric oxide, magnetic oxide of iron, several hydrocarbons 

 and their derivatives, a number of the pyridine series and 



