PLANTS FOR CONGESTED CITY DISTRICTS 119 



providing it receives a certain amount of care. The common arborvitae 

 has generally proved a failure. The exact reason why conifers are so 

 unsuccessful has not so far appeared. Their short life seems to be due 

 to the accumulation of soot which clogs the pores of the leaves and 

 slowly suffocates them. They transpire so much water also during 

 the hot summer droughts that they need an excessive amount of 

 moisture, and they need numerous showers or washings from the 

 hose also to keep them clean and cool. As most evergreens grow- 

 ing under city conditions do not get any care they rarely succeed, and 

 when they do live, they lose their colour and are therefore not recom- 

 mended. 



As a rule, native collected plants seldom or never succeed when 

 taken directly into the congested city districts, and only those plants 

 among the deciduous shrubs and trees which are smooth-leaved are 

 to be recommended for trial. 



LIST OF PLANTS FOR USE IN CONGESTED CITY DISTRICTS 



A. TREES. This group contains trees which may be used with a 

 great deal of certainty that they will thrive under city conditions of 

 congestion and dusty atmosphere. Wherever possible, these trees, 

 especially evergreens, should be thoroughly sprayed at frequent 

 intervals to wash a considerable portion of the dust from the surface 

 of the leaves. 



Abies concolor 



White Fir 

 Aesculus hippocastanum 



Common Horse-chestnut 

 Ailanthus glandulosa 



Tree of Heaven 

 Celtis occidentalis (North only) 



Nettle Tree 

 Cercis canadensis 



Red-bud 

 Crataegus (in variety) 



Thorn 

 Fraxinus (in variety) 



Ash Tree 

 Ginkgo biloba 



Maidenhair Tree 

 Juniper us virginiana 



Red Cedar 

 Picea pungens 



Colorado Spruce 



Pinus montana mughus 



Dwarf Mountain Pine 

 Pinus sylvestris 



Scotch Pine 

 Platanus orientalis 



Oriental Plane 

 Quercus palustris 



Pin Oak 

 Robinia pseudacacia 



Black Locust 

 Salix (in variety) 



Willow 

 Sophora japonica 



Japanese Pagoda Tree 

 Tilia europaea 



European Linden 

 Tilia tomentosa 



Silver Linden 

 Ulmus campesiris 



English Elm 



