ON TREES AND SHRUBS IN LARGE TOWNS. 287 



I. With regard to "what to plant," we have but little 

 to guide us beyond the knowledge derived from observa- 

 tion and experience. We know that certain trees flourish 

 in certain towns take the Plane tree in London as an 

 example whereas another tree similar in appearance to 

 the ordinary observer languishes, and a third quickly dies. 

 T have never yet met with a complete solution of this 

 problem, nor am I prepared to offer one. I can only 

 suggest probable causes. We know that some trees thrive 

 best in a heavy soil, some in a light one ; some in a dry 

 soil, some in a moist or wet one ; some like a warm 

 climate, some a cold one. We know that trees derive 

 their nourishment partly from the soil through their roots, 

 and partly from the air through their leaves trees breathe 

 and perspire through their leaves. The leaves are fur- 

 nished with numerous pores or openings on both their 

 surfaces, through which the functions of breathing and 

 perspiring are carried on. These openings vary in size 

 and number in different species of trees and plants. This 

 variation may probably account in some measure for 

 certain trees sustaining better than others the effects of 

 living and breathing in an impure atmosphere. Again, 

 it may be that the digestive organs of some are stronger 

 or less unfavourably influenced than others by bad air. 

 And here I would remark that by bad air I do not mean 

 simply fog and smoke, bad as those are, but air further 

 polluted by the noxious gases constantly streaming into it 

 from various chemical works which exist in most large 

 towns. I witnessed lately a case which illustrates this 

 remark. A row of Aucubas had flourished for years in a 

 large town, despite of smoke and fog, but perished shortly 

 after a manufactory of chemicals was raised near to 

 them. 



The Plane tree (Platanus orientalis var.) grows well in 

 London and some other large cities and towns in England 

 where the Chestnut, the Larch, and others are not quite 

 satisfactory, and where the Coniferae, with the exception of 



