150 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



The evidence on which this opinion is founded is derived (1) 

 from observation of the behaviour of plants under different 

 conditions of cultivation during foggy weather, (2) from actual 

 experiments in which the special conditions were under control. 



The action of a continuous drip of moisture on foliage in a 

 closed experimental chamber, in which the confined atmosphere 

 contains small quantities of sulphurous acid gas, is to mitigate 

 the immediate damage so far as the leaves, thus continuously 

 moistened, are concerned. 



The degree of humidity in a house, where sulphurous acid is 

 present, is a matter well worthy of attention, and one which I 

 have under observation. The problem is a complex one, and I 

 hope to be able to communicate my results later. 



In a dry atmosphere the sulphurous acid, for the most part, 

 acts as such directly on the living protoplasm. In a humid one 

 it is more rapidly oxidised into sulphuric acid, which has an 

 entirely different action, I apprehend, on vegetation, histologically 

 distinct from the first mentioned. It would, however, be im- 

 proper for me to draw any general conclusions from observations 

 as yet incomplete. 



Another measure, which may be ultimately shown to be 

 practicable, is that of absorbing the most poisonous substances 

 in the fog by using some substance as an absorbent, itself 

 innocuous to vegetation. 



A more practical method is to keep the fog out of the plant- 

 house, rather than to try and neutralise its action after it has 

 entered. So long as cultivators grow plants, susceptible to the 

 impurities of fog, in houses with open glazings in winter time, 

 of course this is impossible. 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. The 

 horticultural engineer could easily manage this. Filtered air 

 could be supplied, as it is to the House of Commons, by pumping 

 through several inches of cotton wool or by some other method ; 

 whilst the illumination could be supplemented by a judicious 

 use of the electric light. Herve-Mangin showed, so long ago as 

 1861, that a plant could manufacture organic matter by the aid 

 of artificial light, and the results of Siemens' more recent ex- 

 periments are familiar. 



