Arthur G. Ruston 391 



In Park Square, near the centre of the city, the laurel, aucuba and 

 rhododendron are deciduous; while in Hunslet, the heart of industrial 

 Leeds, even the box becomes deciduous, and the laurel is killed off in 

 about two years. 



Of the evergreens, the most susceptible are the conifers. These trees 

 are xerophytic; their natural habitat is in a pure atmosphere at a high 

 altitude, where the winds are high and the barometric pressure low, and 

 where consequently evaporation from the leaf surface will be great. 

 The soil, however, will be shallow and the roots none too plentifully 

 supplied with moisture; hence there will be a constant necessity to 

 husband the water supply as far as possible. This end has been effected 

 in the evolution of the plant by the development of small leaf surface, 

 and sunk stomata. Both of these characteristics, while useful in the 

 natural habitat of the conifers, prove their undoing in a smoke-infested 

 area. Conifers planted in Hunslet I have seen killed off in less than 

 three months. Twelve years ago, more than twenty conifers were planted 

 in the grounds of the Leeds University, one mile north from the centre 

 of the city. At the end of three years not one was alive. The only two 

 localities in Leeds, in which conifers attain even a moderate growth, 

 are Roundhay and Weetwood, which the earlier investigations showed 

 to possess the least smoke-infested atmosphere. 



It is doubtful if they would ever do well in any district, where the 

 annual deposit of soot amounts to more than 50 tons per square mile. 



Plants whose leaves are possessed of a crinkled hairy surface, thus 

 easily catching the soot, and of a thin cuticle readily damaged by the 

 acid rain, are also particularly sensitive to smoke pollution. On the 

 other hand, those possessing a hard smooth leathery type of leaf with 

 thick epidermis, like many of the alpines, pinks, carnations, auriculas, 

 London pride, and iris, are particularly resistant. 



Thus the primrose does badly in Hunslet, makes little or no growth, 

 rarely flowers, and never lives through more than one winter; while the 

 auricula is as hardy as possible, and not only lives but thrives, grows 

 and spreads. One border five yards long, which last spring was a mass 

 of bloom, is the result of five years' propagation from four small plants. 

 The geranium can be grown in a smoke-infested area, but the calceolaria 

 is always a failure. 



Perhaps no plant of this type gives a better index of the amount of 

 smoke pollution than the hollyhock. Six years ago, eight hollyhocks (all 

 propagated from the same parent plant) were planted in tubs containing 

 soil taken from the same field of the Experimental Farm of the University 



