84 SMOKE AND TREES. 



What has been said is chiefly applicable to broad-leaved, and 

 especially deciduous trees. The same form of injury is, however, 

 not awanting among conifers, although possibly on the narrow 

 leaves it is not so apparent at first sight. On careful examination, 

 however, the leaves are frequently found spotted in the same 

 manner, and at times the spots go right round the needles, and 

 cause the outer portion to die off, giving the injury the appearance 

 of that caused by frost. The result in both cases is the same, the 

 green living matter being killed, the power of the plant for carbon 

 assimilation is reduced, and causes the leaves to fall prematurely. 

 The balance of nature is interfered with, and the health of the 

 trees in this way seriously impaired, making them more susceptible 

 to attack from other causes, either by insects or fungi, especially 

 the latter. Attacks by insects on conifers are fortunately less 

 frequent on the trees which are most affected by smoke than one 

 would expect. Indeed those insects which breed on sickly pines are 

 conspicuous by their absence in this locality. Although they are 

 occasionally found, there has 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 piniperda), 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 

 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, par- 

 ticularly 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 remark- 

 able 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, 



