50 
It is obvious that the rain washes this acid into the 
soil, so that not only the leaves but the roots also suffer 
from its effect. Rain water collected in or near our towns 
is always slightly acid, and a great difference can be 
observed in the growth of seedlings, some of which are 
watered with ordinary rain water and others with rain 
water in which the acid has been neutralised. A consider- 
able number of striking experiments on this point have 
been made by Mr. Ruston, of the Leeds University. The 
lesson they teach us is that the soil of gardens or allot- 
ments near our large towns should be well treated with 
lime, so as to neutralise as far as possible the acidity which 
is caused by the rain washing the smoky atmosphere. 
A consideration of the fact that this smokiness and acidity 
of the air is greater in winter than summer suggests that 
a dressing with lime in the spring before growth recom- 
mences would be especially beneficial. Experience has 
also taught us that many biennials are better wintered 
under glass than when left in the open, even when they 
readily withstand the frost. A glance at the condition 
of the lights of a cold frame will show us what a coating 
of soot we have prevented from collecting on the leaves. 
A really penetrating fog, however, will get into frames 
and greenhouses, and may often do considerable damage 
to the delicate blooms of Orchids and to many other 
flowers, besides causing in some plants the leaves to become 
discoloured or to fall.* 
* See F. W. Oliver on “ The Effects of Urban Fog on Culti- 
vated Plants.” Journal of the Royal Horticultural Society, 
vol. xili, 1891. 
