ON THE EFFECTS OF URBAN FOG UPON CULTIVATED PLANTS. 143 



however, intermediate stations in this quarter, at a distance of 

 12 to 10 miles, are relatively free from the worst forms of fog, 

 the local industries of the Medway Valley are not improbably 

 answerable for the severe results reported from this town. All 

 my correspondents emphasize the non-hurtful nature of the sea- 

 fogs prevalent in this quarter. To the north and north-east 

 the fog-effects do not extend to such extreme distances, and the 

 conditions for winter cultivation are consequently more favour- 

 able on that side of the metropolis. Mr. E. Mawley, of 

 Berkhampstead, has furnished me with some interesting 

 meteorological details regarding fogs extending to this locality 

 (26 miles N.W.) 



The tabulation of the information bearing on the subject of 

 this paragraph will form a valuable appendix to my detailed 

 report. 



III. The Fogs of the Winter 1890-91.— It is needless to 

 say that the past winter has been one singularly favourable for 

 the purposes of an investigation of this character. The season 

 opened with a severe fog of short duration during the second 

 week of October, which left its traces on vegetation in the 

 London area. This was the only serious instance of a fog on 

 which observations of hardy plants could be made, as the con- 

 ditions were not complicated by the presence of frost. I am 

 indebted to Mr. C. T. Druery for an interesting account of its 

 effects, unprecedented in his experience, upon his collection of 

 hardy Ferns at Forest Gate. Though there were minor fogs 

 during November, it was during the long periods before and after 

 Christmas, and again in February, that all the worst effects were 

 exhibited by vegetation under glass. These two spells differed 

 considerably in their nature. The Christmas fogs were accom- 

 panied by exceptionally severe frosts, were on the whole much 

 darker overhead, and contained a larger amount of noxious 

 matter. In addition to this, the duration of daylight was con- 

 siderably shorter than in February. On the other hand, though 

 in February the fogs were exceedingly opaque, the general 

 average of light reduction was not so great as at Christmas. The 

 vertical extent of the fogs in February was such that on many 

 occasions the sun was able to partially disperse them for a short 

 period at noon. 



Both fogs had a marked effect on flowers, but on the whole 



