THE INJURIOUS EFFECTS OF SMOKE ON TREES. 125 



not been noted anything like what might be termed a general 

 attack, which would lead one to the conclusion that they have an 

 aversion either to the dirty trees or the impure atmosphere. 

 This is especially the case with the Pine Bark Beetle {^Hylurgus 

 2nni2)erda), which very often proves to be a serious pest in pine 

 woods, where the trees are in such a state of health as obtains in 

 the surrounding district. 



Effects of Soot. — The next point of importance is the sooty 

 part of smoke and its effects. It is argued by some that this 

 factor is not at all injurious to broad-leaved plants, and especially 

 to deciduous species, and I do not doubt but that, with such 

 plants, it is of minor importance compared with the effects of acid 

 gases, but I am inclined to believe that it does considerable harm, 

 particularly to Evergreens ; an instance of this was brought under 

 my notice last summer in Messrs Smith and Simons' Nurseries at 

 Kennishead. There were several days of very dense fog, towards 

 the end of January 1899, which blackened everything to a re- 

 markable degree, the leaves of Evergreens being simply painted 

 with soot, and, for the want of a good day's rain immediately 

 following, it got fixed on and adhered to some extent for a 

 considerable time, the result being well demonstrated in the 

 instance referred to, where a few plants in a plot of Aucubas 

 were, by a mere chance, syringed and freed from this coating, with 

 the result that they looked healthier all the year, and made a better 

 growth than the average of the remainder of the plot. This 

 seemed to show that the soot on the leaves has to some extent a 

 prejudicial e£Fect on the plant, not in the way of injuring them, 

 for thote that were not cleaned were free from any particular 

 injury by acid in the soot, but, in my opinion, by the cofating in 

 some way affecting the action of the chlorophyll, presumably by 

 the sun's rays having less power, through having to penetrate 

 this film or scum on them. This may albo apply to deciduous 

 plants, but in a less degree, because their leaves have a much 

 shorter life, and have not the chance of becoming coated to the 

 same extent, although that tbey do get blackened any one may 

 prove by drawing a few leaves through a clean hand, or, better 

 still, through a clean white handkerchief. It is admitted, how- 

 ever, that the injury done by smoke in this way to such trees is 

 very little compared to what happens with conifers, which, with 

 a few exceptions that may be overlooked, are Evergreens. In the 

 first place, the particles of soot in the air seem to adhere more to 

 the leaves of the majority of such trtes than is the case with the 



