NAT LU IVAL. SC LING - 
A Monthly Review of Scientific Progress. 

NO: 163 Vor sii cUNE 1893: 

NOTES AND COMMENTS. 
Foc*aND VEGETATION. 
MONG the most interesting of last month’s reports is that issued 
in the Fournal of the Royal Horticultural Society (part 1, vol. xvi.) by 
Professor F. W. Oliver, who publishes the second instalment of his 
observations on the effects of urban fog on plants cultivated under 
glass. The effect is twofold; in the first place, we have to consider 
the serious loss of light; in the second, the poisonous substances 
present in the air. 
The general tone of plants, especially of those fond of sunlight, 
must be considerably lowered by the often long persistent, dull winter 
weather, with its frequently-recurring fogs. The assimilation of 
carbonic acid is interfered with, while the transpiration of water 
vapour from the leaves is almost at a standstill. The roots are not 
affected, and continue to absorb water from the soil, especially in the 
case of stove plants, where they are kept by the warmth in a state of 
marked activity. Hence the cells of the plant become unduly dis- 
tended with water. Finally, owing to faulty circulation in the 
intercellular passages, access of oxygen from without is impeded, 
while the supply normally received from the decomposition of carbonic 
acid in assimilation is almost entirely cut off; respiration is checked, 
and substances tend to accumulate in the cells from want of complete 
oxidation. Thus the whole leaf-mechanism is out of gear. In this 
enfeebled state the plant is exposed to the attacks of sulphurous acid, 
hydrocarbons, and other noisome fog constituents, and the result is 
lamentable, often, indeed, fatal. 
Professor Oliver distinguishes two classes of injury, produced by 
distinct causes. First, cases in which the leaves show local discoloura- 
tions, particularly at the tips and margins, while the unaffected 
parts remain fully functional, and the leaf does not fall; secondly, 
2D 
