TREES IN CITIES. 93 



II. Trees in Cities. 



An interesting article on the trees which will thrive in London 

 appears in the Times, and from it we extract the following : — ■ 



The choice of trees for town planting is severely restricted, 

 owing to certain adverse conditions which have not to be taken 

 into account in the open country. Chief among these conditions 

 are : — excessive drainage, which renders the soil dry and in- 

 hospitable ; the scorching heat caused by the reflection of 

 sunlight from pavement and masonry ; and lastly, an atmosphere 

 loaded with the waste products of coal combustion. In most 

 continental cities, where wood is chiefly burnt, it is only the 

 first two of these conditions which seriously affect tree growth; but 

 where coal is the universal fuel, as it is in the towns of the 

 United Kingdom, only very few species of trees can maintain 

 vigorous growth. Coal smoke acts inimically upon vegetation 

 in two ways — mechanically and chemically. Mechanically it 

 clogs the pores of the plant by depositing upon them a coating 

 of solid carbon of soot ; chemically it destroys the leaf tissues 

 by sulphurous acid. 



Its presence deprives sunlight of some important properties ; 

 for, although the rays may beat upon the streets with almost in- 

 tolerable heat, town-dwellers are never sunburnt, showing that 

 the chemical rays have been intercepted or altered. These 

 adverse conditions are intensified in proportion as the town 

 extends, until, as has happened in London, there is not a single 

 tree native of our humid climate which can be used for street 

 planting, and we are compelled to employ a very few exotic species. 



Moreover, London is built mainly on the low-lying shores of 

 a muddy estuary, naturally very subject to winter fogs, which 

 though innocuous in themselves to arboreal life, become highly 

 deleterious when charged with solid carbon, carbon dioxide 

 and sulphurous acid. In the public parks and larger squares, 

 where the heat is not so intense nor the radiation so rapid 

 as among the houses, several species may be grown which 

 would perish in the streets ; but even so, it would be hopeless 

 now to plant young trees in the belief that they would ever 

 attain the stature of the elms and Spanish chestnuts in Hyde 

 Park and Kensington Gardens. The old trees there and else- 

 where in London attained maturity before the atmosphere had 

 become so heavily charged with deleterious matter as it is now. 



