82 SMOKE AND TREES. 



and sheep or cattle put on it after the growth has stopped, they 

 will almost starve rather than eat it. Even rabbits will scarcely 

 attempt it after the season has well advanced. They prefer 

 gnawing the bark of trees or shrubs, the outside of which is perhaps 

 no cleaner than the grass, but they nibble that off and get into 

 the fresh under-bark. Experience proves that the ravages of 

 ground game on trees are much worse in smoky localities than in 

 others ; the reason being, as already stated, that they will scarcely 

 touch the old grass after the month of November. That is, 

 however, an indirect result, and one which can very easily be 

 removed if the parties concerned are willing. 



The direct results of injury from smoke constitute a more 

 serious problem, with which it is difficult to grapple. It is even 

 questionable if it can be absolutely remedied. The damage directly 

 done by smoke and its allies is of a threefold nature. First, there 

 is the killing of the living matter in the green parts of plants, 

 particularly in the leaves, caused by acid in the smoke ; second, 

 the clogging-up of the stomata of certain plants by soot, and the 

 general coating-over with the same of all their parts ; and, third, 

 the effect of the smoky atmosphere in obscuring the sun. It is 

 difficult, or even quite impossible, to define exactly the amount of 

 damage done by each cause, because their action is always 

 combined. Yet it may be as well to consider separately as far as 

 practicable how the plants are affected by each of the causes 

 detailed above, afterwards looking at the effect of their combined 

 action. 



Effects of Acid. — The gaseous acid in the smoke enters into 

 the leaves during the process of carbon assimilation, at once 

 attacking the living matter in the cells, and destroying it by oxidising 

 or bleaching it, therefore rendering the affected portion absolutely 

 useless. A leaf affected by acid, if held up to a strong light, 

 shows little clear spots wherever the action has begun. Through 

 time, these spots usually become brown, almost black in some 

 plants, and they might readily be taken for an attack by a fungus. 

 On a closer examination, however, a clear margin is seen round 

 the coloured part, which distinguishes it from any disease. This 

 form of injury is generally attributed to sulphurous-acid gas, which 

 is always given off in the burning of coal and particularly dross, 

 in varying quantities, according to the quality of the article being 



