SMOKE AND TREES. 85 



syringed and freed from this coating, with the result that they 

 looked healthier all 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 effect on 

 the plant, not in the way of injuring them, for those that were not 

 cleaned were free from any particular injury by acid in the soot, 

 but, in my opinion, by the coating 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 also 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 they 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, however, 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 trees 

 than is the case with the others. This may be accounted for, with 

 some, by the resinous and sticky nature of the skin of the leaves, 

 and with others, such as Cupressus etc., it is due to some extent 

 to the position of the leaves, which forms a kind of trap for 

 collecting it. Further, the formation of the stomata permits of 

 such particles entering in, and more or less choking them, which 

 means partial starvation and suffocation for the plant. Some 

 leaves taken from Scots Firs on Pollok, and cut into sections, 

 showed almost every pore to be more or less closed in this way. 

 This is bound to impair the health of the plants in no small 

 degree, through the leaves being unable to perform their functions 

 properly, and it also causes premature leaf-shedding, which is, 

 however, greatly assisted by the leaf-shedding fungus ( Hysterium 

 pinastri), a disease which, unless in seed-beds, is not characterised 

 as of a serious nature, but, when the young pine trees are in an 

 unhealthy state through the effects of smoke, they are attacked 

 all over by it, with very serious results. From this cause, last 

 year, over 10,000 Scots Fir plants between 12 and 20 years of age 

 had to be cut down on Pollok Estate. 



Effects of Darkened Atmosphere. — This brings us to the 



