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. Solotaroff, Shade Trees in Towns and Cities, p. 4 (1911). 
2. See A. Rigg 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 Trans. Koy. 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 form 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 Cerris, 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 choking by soot of the stomatic openings 
of the leaves. Scots pine, 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 growing season with nothing but the previous 
year’s leaves adorning them, instead of two years complete and the greater 
portion of the third, thus giving them a thin, tufted, stunted, and unhealthy 
look.” The diminution of increment of growth in the Pollok plantations 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 percent. 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 Medlon Institute, Philadelphia, Smoke 
Investigation, Bulletin No. 7 (1913), ‘‘The Effect of the Soot in Smoke on 
Vegetation.” See also American Forestry, Dec. 1917, p. 732. A. L. Bakke, 
in Jowa State College of Agriculture, Bull. 145 (1918), established that the 
vegetation about a manufacturing concern can be mapped in concentric zones, 
