TREES IN TOWNS 57 



The careless laying of water pipes and electric mains causes 

 the death of many trees. Changes in the level of a road 

 or street often involve the destruction of trees. The old 

 tree in a village, at a cross-roads, or in the market-place of 

 a small town, ought to be guarded with great care, as it 

 gives to each place its own peculiar aspect, and causes it to 

 linger in the memory of those who have left their early 

 home. 



NOTES 



1. See W. SolotarofT, Shade Trees in Tawns and Cities, p. 4 (1911). 



2. See A. Kigg in Journ. R. Sanitary Inst, xxvii. p. 160 (1906). 



3. An interesting account of the effect of the smoke of Glasgow on trees 

 growing on the Pollok estate is given by John Boyd in Travs. lioy. Scot. 

 Arbor. Soc. xvii. 122 (1904). He distinguishes clearly the effects of acid 

 in the smoke, of soot, and of the darkened atmosphere. " A leaf affected by 

 acid, if held up in a strong light, shows little clear spots, wherever the action 

 has begun. Through time these spots usually become brown, almost black 

 in some plants. A clear margin is seen around the coloured part, which 

 distinguishes it from any fungus disease. This foini of injury is generally 

 attributed to sulphurous acid gas, and may be seen more or less in almost all 

 species of broad-leaved trees growing in a smoky district ; but the various 

 trees are not all affected to the same extent." Horse-chestnut is very badly 

 injured in this way. The oaks, especially Quercus Ccrris, withstand acid in 

 the smoke better than any other species. Ash is next in resisting power, 

 followed by elm and sycamore. Service trees, birch, and rowan are little 

 affected, and are very suitable for smoky localities, as they are not so partial 

 to a good soil as the trees just mentioned. Boyd correctly attributes the ill- 

 health of conifers at Pollok to the clicking by soot of the stomatic openings 

 of the leaves. Scots jiine, which suffers very badly, showed when the needles 

 were examined almost every pore to be more or less closed by soot. The 

 leaves of Scots pine also fall off prematurely, "it being quite common to see 

 them at the beginning of the gi-owing season with nothing but the previous 

 year's leaves adorning them, instead of two years complete and the greater 

 ])ortion of the third, thus giving them a thin, tufted, stunted, and unhealthy 

 look." The diminution of increment of growth in the Pollok ))lantations is 

 also remarkable, amounting in the case of broad-leaved trees, like oak, ash, 

 sycamore, beech, elm, hornbeam, birch, service and rowan, and in Austrian 

 pine, to 10 or 20 per cent, and in the case of the worst sufferers, Scots pine, 

 Weymouth pine, and spruce, to 20 to 40 per cent. The number of stems per 

 acre is also reduced, so that it is absolutely impossible to cultivate trees 

 successfully from a commercial point of view in any smoky locality. 



The effect of the smoke of blast furnaces, of numerous passing locomotives, 

 etc., on neighbouring trees in narrowing the annual rings is well described 

 and illustrated by J. F. Clevenger in Mellon Institute, Philadelphia, Smoke 

 Investigation, Bulletin N'o. 7 (1913), "The Effect of the Soot in Smoke on 

 Vegetation." See also American Forestry, Dee. 1917, p. 732. A. L. Bakke, 

 in loiva State College of Agricnlturc, Bull. 14f, (1913), established tliat the 

 vegetation about a manufacturing concern can be mapped in concentric zones, 



