TEEES IN TOWNS 45 



Trees should never be planted in narrow streets, and 

 can only safely be planted when the footpaths also are not 

 narrow. It is objected to trees that they render the 

 thoroughfare moist ; but such moisture as they occasionally 

 cause does no harm to the surface of the roads, and on the 

 contrary keeps them in better condition than dry dust 

 would do. Some people do not like the fallen leaves of 

 trees, but the trouble of removal is very slight. 



That towns are unhealthy to vegetation and especially 

 to trees is well known ; and this subject is relevant, as 

 illustrating the strange fact when one thinks of it, that 

 towns owing to various causes are unhealthy, just in the 

 same way to human beings as they are to trees. First, 

 there is the smoke of towns, which is a wicked waste of 

 coal and entirely preventable. Evergreen trees in London 

 are quickly coated over in winter with a dark shining 

 carbonaceous product (2), soot, and need washing in the 

 Botanic Garden of Regent's Park. The smoke of towns (3) 

 causes the pores of the leaves to be blocked, thus checking 

 transpiration. Every dirty plant is practically living in 

 twilight, as the soot reduces the assimilation of carbon 

 dioxide by the leaves, depriving them of their most 

 important source of food. Last of all, the sulphur contained 

 in ordinary coal when burned is changed into sulphur 

 dioxide, which ultimately forms sulphuric acid, a deadly 

 corrosive poison to the leaves (4). 



The soil under streets in towns is unfertile, and is often 

 very poor, being composed of building debris, etc. ; but its 

 main defect is its dryness, as owing to the modern 

 pavement all the water, which falls as rain, runs off into 

 the sewers, finding its way into the sea, and never reaches 

 the soil, where the roots of the trees are. Drought is the 

 greatest enemy of trees, as the latter, owing to their 

 extensive surface of foliage, require enormous quantities of 

 water. The only trees that thrive in streets in towns are 

 those able to resist drought. 



The soil, according to Wieler, being made acid by the 

 action of the sulphur compounds in the soot, loses its 



