14 



NA TURE 



[November 5, 1891 



General, they do not confirm the popular impression that 

 fog is a deadly scourge ; at the same time, it is beyond 

 doubt that an atmosphere charged with soot, dust, and 

 empyreumatic products is an unwholesome atmosphere 

 to breathe ; but I think that the principal cause of the 

 great increase of death when fogs occur is attributable 

 rather to the sudden fall of temperature which usually 

 accompanies fog, than to the fog itself. 



So many toxic effects are now traced to the action, 

 direct or indirect, of bacteria, that it is satisfactory to 



bare, and it is impossible ever again to recover them into 

 sightly specimens. (2) The toxic influence of the fog. 

 This is most striking. It is illustrated in the most forcible 

 way by the inclosed memorandum. I attribute it in the 

 main to sulphurous acid, though I cannot help suspect- 

 ing that some hydrocarbon may also have something to 

 do with it. The toxic effect varies from one plant to 

 another, some are scarcely injured, others are practically 

 killed." He adds : --" I hope you will be able to arouse 

 some interest in this horrible plague. If the visitation of 



Fig. 2, 



learn, from the experiments of Dr. Percy Frankland, that 

 fogs do not tend to concentrate and nurture them, for he 

 found there were remarkably few bacteria in London air 

 during a time of fog. The deleterious action of town 

 fogs on plants is more marked and more easy to inves- 

 tigate than its effect on animals. Nurserymen have 

 long known from experience that a town fog will pene- 

 trate even their heated greenhouses, and with certainty 

 will kill many of their plants, specially their orchids, 



last year is annually repeated, it must in time make all 

 refined horticulture impossible in the vicinity of London." 

 I append to this paper the very interesting and im- 

 portant report to which Prof. Dyer refers, from Mr. W. 

 Watson, " On the Effect of Fog on Plants grown at Kew." 

 This fog action on plants is so clearly marked, and so 

 deadly, that it has, I am happy to say, led the Horticul- 

 tural Society, aided by a grant from the Royal Society, to 

 undertake a scientific investigation of the matter. Plants 



I890-I89J 



Fig. 3. 



tomatoes, and, in fact, most tender and soft-wooded 

 plants ; but on this point, I cannot do better than read 

 to you what the Director of Kew Gardens, Prof. Thisel- 

 ton Dyer, says in a letter to me :— " With regard to 

 plants under glass, the effect of fog is of two kinds — (i) By 

 diminishing light. This checks transpiration. The plants 

 are therefore in the condition of being over-watered. A 

 well-known consequence of this is to make them shed 

 their leaves wholesale. Many valuable plants which 

 ought to be well furnished with foliage become perfectly 



NO. I 149, VOL. 45] 



are so much more easily dealt with than people, all the 

 circumstances of their attack by the fog and its immediate 

 results so much more easily noted and traced, that the 

 investigation has already yielded important lesults, and 

 we shall, I hope, hear from Prof. Oliver— who is devoting 

 himself specially to the investigation— seme account of 

 his latest results. A maiked and admitted difference 

 between town and country fog is, that while a country 

 fog is harmless in a greenhouse, a town fog will produce 

 most destructive results. 



