Annals of Horticulture. 



gredient of these smoke-fogs appears to be sulphuric acid. 

 These fogs injure plants, therefore, both by reducing the light 

 and "in the formation of actual corrosions of portions of the 

 leaf-surface." The fogs injure both buds and leaves, causing 

 them to fall, and they sometimes destroy outright tender 

 seedlings of cucurbits, tomatoes and some other plants. The 

 chemical composition of one sample of the fog deposit from a 

 greenhouse roof was as follows : About 40 per cent, mineral 

 matter, 36 per cent, carbon, and 15 per cent, of hydrocarbons. 

 There was 2 to 3 per cent, of metallic iron in minute par- 

 ticles. Sulphuric acid was present to nearly 5 per cent, and 

 hydrochloric acid 1^. per cent. The report suggests several 

 Fog. remedial measures. In foggy times in cities the temperature 

 should be kept low and the roots should be watered sparingly. 

 "Everything should be done to tax the vegetative organs of a 

 plant to the least possible extent, when any of the vital func- 

 tions are interfered with, as in dull, foggy weather." There 

 is some reason to believe that moisture upon the leaves less- 

 ens the injury from the acid. It is possible that some 

 practicable way may be found of straining or filtering foggy 

 air upon its entrance into the house, or some absorbent may 

 be found which shall render the fog innocuous. It is also 

 thought that the electric light can be used to advantage in 

 foggy weather. The most promising remedy, in the opinion 

 of Professor Oliver, is to keep the fog out of the house. " It 

 is to be hoped some metropolitan grower will pluckily face the 

 situation and construct a range for winter use, which can be 

 made at will absolutely fog-proof, with close glazing, triple 

 doors and padded ventilators." 



