144 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



at Christmas, to instance only one genus of plants, Cypripedium, 

 the effects were much more marked. Cypripedium is perhaps 

 as little affected by fogs as any genus of Orchids I have met with. 

 Yet, in a large collection, continuously under my observation, it 

 was patent that the damage done was markedly less in February 

 than at Christmas. In the collections of plants under observa- 

 tion, the damage to foliage was also greater during the Christmas 

 fogs ; this both as regards the dropping of leaves, which I have 

 reason to believe to be greatly brought about by the reduction of 

 light for a lengthened period, and also in the formation of actual 

 corrosions of portions of the leaf-surface. 



It must be remembered, in estimating the relative damage 

 caused by these two fogs, that the earlier one destroyed a greater 

 part of the foliage of very many soft-wooded plants, so that there 

 was less surface exposed for attack on the second occasion. Never- 

 theless, so favourable were the circumstances during the latter 

 part of January and the first week in February that rapid 

 growth had in many cases taken place. If we narrow the com- 

 parison to the damage (corrosions) sustained by young and 

 relatively unprotected leaves during the two periods, without 

 doubt that at Christmas was immeasurably greater than in 

 February. These remarks are based on observations on collec- 

 tions continuously under my eye, and situate in the worst 

 districts. Full details are not yet to hand from correspondents 

 at outlying stations, so that it is possible I may have to modify 

 these observations when I come to take a general survey. (Thus 

 at Kew, the ill effects noted after the February fogs were quite 

 as bad as at Christmas, whilst further east the reverse was the 

 case. Other considerations confirm the view that in February 

 the fog-nucleus was several miles further west than at Christ- 

 mas.) I have in my notes full details of the damage obtaining 

 from these fogs from many sources, but with these horticultural- 

 ists are, in general, only too familiar, and they may well be 

 reserved for the report on the whole question. 



IV. Constitution of Fog. — On a purely chemical question, 

 such as that of the constitution of fog, I am scarcely entitled 

 to speak. However, since at the outset of this inquiry it was 

 deemed advisable to obtain as much information on the 

 matter as possible, with especial reference to those components 

 deleterious to vegetation, I will state briefly what has been done. 



