56 



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. Ram water collected in or near our tow^ns 

 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 

 v/ater in wdiich 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, e^'en when they 

 readily withstand the frost. A glance at the condition 

 of the lights of a cold framie 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. xiii, 1 891. 



