FOG, FLOWERS, AND FOLIAGE 49 



learning what the poison consists of, and in tracing exactly 

 how the injuries come about, as would suffice, one would 

 imagine, to discover a cure. Oddly enough, more 

 poisons are found in fog than even coal-burning altogether 

 accounts for ; the exact nature of some of the substances 

 which are present in the atmosphere of foggy weather 

 is a matter about which scientists themselves confess to 

 ignorance. 



Still, there is one thing on which all agree, and that is 

 the perfect harmlessness of clean mist. Neither mountain 

 nor country mists do any wrong to plant life, and from 

 the coasts of Kent and Sussex, Essex and Norfolk, come 

 assurances of the innocuous character of sea-fogs. 



Of the known impurities of town-fog the following list 

 gives most of those suspected of being inimical to plants. 

 "Suspected" is the scientific way of putting it. Our 

 scientists are wary ; they must be, for they know how 

 everybody weighs their words ; and besides that, they can 

 never be sure what fresh discoveries will be made to- 

 morrow ; the latest are oftentimes upsetting. 



The amount of miscellaneous ingredients that enrich 

 a London fog is startling. Our list is taken from an 

 analysis of the deposits left on the glass roofs of plant- 

 houses at Chelsea and Kew during the severe fogs of 

 February, 1891 : — 



Carbon, hydrocarbons, organic bases, sulphuric acid, 

 hydrochloric acid, ammonia, metallic iron, and magnetic 

 oxide, with other mineral matter, chiefly silica and ferric- 

 oxide. Sulphuric acid, it seems, is the principal cause of 

 injury to trees and shrubs, and sulphurous acid to her- 

 baceous and soft- wooded plants. 



The efiFects of fog are seen sometimes in the breaking- 

 down of the plant, sometimes in its discoloration ; leaves 

 gradually turn yellow, progressing from below upwards, 

 and they drop off in the order in which they showed the 

 change of colour. Thus two things have happened : 



E 



