SMOKE AND TREES. 83 



consumed, and there is little reason to doubt but that it is the 

 chief factor in the mischief, although there are other gases given 

 off in limited quantities from various works which assist in the 

 injury to vegetation. The effects of acid may be seen more or 

 less in almost all species of broad-leaved trees growing in any 

 smoky district, and is very easily recognised in its early stages on 

 trees with coloured leaves. The various trees, however, are not 

 all affected to the same extent, neither is any one species affected 

 alike during all the growing season. It seems to be worst when 

 the leaves are at their most active stage, very young leaves not 

 being so readily injured as those that are fully developed, and are, 

 so to say, in full swing at the process of carbon assimilation. 

 Neither are leaves so readily affected when the season has well 

 advanced and their working power has begun to wane. On 

 Pollok Estate, this form of mischief is particularly noticeable in 

 the early part of the season, no doubt because, at that time, east 

 and north-east winds are more prevalent, and drive the smoke of 

 the city over the place. On several occasions in recent years this 

 was very noticeable. It so happened that, when the earlier trees 

 had just got into full leaf, we had a continued spell of east wind, 

 with the result that the foliage was very seriously injured. The 

 leaves in many cases no doubt suffered from other causes, 

 which was shown by the edges becoming brown, but there were 

 also decided symptoms of the effects of acid in the manner already 

 mentioned, with very serious results as regards the health and 

 appearance of Horse-Chestnuts. Their growth was entirely stopped 

 until after mid-summer, when nature, trying to recoup herself, 

 sprang away with a young growth, rather a rare occurrence with 

 these trees, which gave them a somewhat remarkable and not 

 altogether pleasing appearance. Among forest trees, Oaks (parti- 

 cularly the Moss-cupped or Turkey Oak) seem to withstand or 

 resist the attack of acid better than any others. Ash may be said 

 to come next, followed by Elm and Sycamore. The Ash, however, 

 has a decided advantage over the others, in that it is generally 

 the last to put forth its leaves, and casts them early, thus having 

 them exposed for a shorter time. Service trees, Birch and Rowans, 

 especially the two former, are also well suited for growth in smoky 

 localities, and are not so partial to a good soil as the others 

 mentioned. 



