120 Mosses and Liverworts of an Industrial City. 



suburbs, including Troydale and Cockersdale, where there are 

 exposures of coal measure, sandstones and shales, which 

 weather to a clay soil carrying pasture and oak. 



It has been shown* that the reduction of the intensity of 

 sunlight, due to matter suspended in the atmosphere, amounted 

 in the worst cases to 40 per cent, in the industrial districts of 

 Leeds, growth being further prejudiced by mechanical obstruc- 

 tion of assimilation and respiration ; by the toxic effect 

 of sulphur compounds penetrating leaf tissues, and by the 

 deleterious action on soil bacteria of free acids washed down 

 by rain. Atmospheric impurities detected at different recording 

 stations were influenced by the less complete combustion of 

 domestic fires as compared with factory furnaces, and by 

 prevalent winds, the cleanest districts being in the north-east, 

 north and west. It is in these districts that the moss flora 

 best maintains itself ; as the industrial centre is approached, 

 mosses decrease, until three only survive to rank with the 

 sparrow as city dwellers. There is evidence that these three 

 plants tolerate the worst atmospheric conditions, provided a 

 favourable minimum of moisture is assured. Their absence 

 from many miles of streets may be attributed to the combined 

 effect of human disturbance, drought and chemical poisoning ; 

 in the midst of barren surroundings, they invade walls moistened 

 by leaking pipes and steam exhausts, and they abound in 

 damp, shady enclosures protected from excessive treading 

 such as may be found at Holbeck Workhouse, East End Park, 

 etc. The precincts of the Parish Church, the riverside near 

 The Calls," Hunslet Moor, and the immediate neighbourhood 

 of the Leeds steel works probably represent the extreme of 

 adverse atmospheric conditions for vegetation, but even there 

 these mosses maintain an existence. 



Some notes on their general distribution taken from 

 standard authors j - show that in addition to smoke resistence, 

 they have an adaptability to extremes of temperature that gives 

 them a claim to ubiquity. 



Ceratodon purpureus. — The most cosmopolitan of all mosses ; 

 throughout almost the whole world from Spitzbergen and 

 Greenland to the Antarctic regions. 



Funaria hygrometrica. — Throughout almost the whole world 

 on walls and rocks and especially on burned soil. 



Bryum argenteum. — Almost everywhere throughout the 

 world — Europe, America, India, Australia, Tasmania, to the 

 extreme limit of terrestrial vegetation in 64 S. 



* The Nature, Distribution and Effects upon Vegetation of Atmospheric 

 Impurities in and near an Industrial Town, by Charles Crowther, M.A., 

 Ph.D. and Arthur G. Ruston, B.A., B.Sc. Journ. Agr. Set., IV., p. 24. 



f Index Bryologicus, E. G. Paris ; ' Handbook of the New Zealand 

 Flora,' J. D. Hooker; Synopsis Muscorum, C. Mueller. 



Naturalist, 



