126 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



others. This may be accounted foi", with some, by the resinous 

 and sticky nature of the skin of the leaves, but with others, such as 

 Gupressus, etc., it is due to some extent to the position of the leaves, 

 which forms a kind of trap for collecting it. Further, the forma- 

 tion of the storaata permits of such pai'ticles entering in, and 

 more or less choking them, which means partial starvation and 

 suffocation for the plant. Some leaves taken from Scots Firs on 

 PoUok, 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 ai'e 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 twelve and twenty years of age had to be cut down on 

 Pollok Estate. 



Effects of Darkened Atmosphere. — This brings us to the 

 third way in which the trees are affected, viz., through the smoke 

 in the atmosphere. I do not know if this source of damage has 

 been much noted, but it is none the less present, although 

 possibly not noticeable at first sight, particularly with trees 

 standing singly. In woods or small thickets of trees, however, 

 its effects are at once apparent, and I believe are much more wide- 

 spread than either of the previous evils. It neither affects the 

 health of trees standing singly, nor those in open woods, so much 

 as it does those in close woods. The treatment of woods within 

 a radius of six or seven miles of the centre of the city, or in any 

 locality where there is much smoke, is entirely different from the 

 ordinary routine. "Woods, notably pine woods, must be kept 

 much opener, to admit of the plants getting sufficient light to 

 keep them in anything approaching a healthy condition, and I 

 am of opinion that the continuous darkening of the atmosphere 

 by smoke must take a great share of the blame for this. How- 

 ever, as previously stated, it is quite impossible to draw lines of 

 distinction between the amount of injury done by each of the 

 various causes, and having now considered how the trees are 

 affected by them separately, a brief consideration of the total 

 injury done in regard to appearance, health and growth, must 

 suffice. 



