156 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 
whether a crop of timber is likely to prove a success or failure 
on a particular site. In a general way, it is true, the conditions 
under which trees grow are sufficiently well known to enable a 
forester of any experience to describe a locality as good, bad, or 
indifferent, or to say with reasonable certainty that Scots pine 
or spruce will grow here, or oak and ash there. So far, no great 
difficulties present themselves. But when the finer distinctions 
between various localities are separated into their component 
parts, as they must be when a detailed examination is made of 
them, it is very difficult to say what value can be placed upon 
them individually. Local climate, soil and situation are all 
extremely complicated factors which co-operate in producing a 
definite effect upon plant-growth, but the relative importance of 
each cannot be estimated with any great accuracy. All we 
know is that they vary the rate of growth, the quality and 
quantity of the timber, and the final development of any 
particular crop to an extent which may render a profit possible 
in one place, or result in a loss in another. Where these factors 
are well pronounced, as in the case of a wet or dry climate, a 
clayey or sandy soil, or an exposed or sheltered situation, their 
effect can usually be recognised, and, according to the species 
concerned, may be favourable or the reverse. But when they 
are either so obscure, or influence one another to an unusual 
extent, it is practically impossible to estimate the effect of any 
one of them individually, and a great deal of planting work 
must always be of a speculative character for this reason. 
ASSESSMENT OF LOCALITY. 
The point which is, after all, of most importance in connection 
with our subject, however, is the extent to which reliable conclu- 
sions can be drawn from a careful examination of the various 
features of local climate, situation and soil. The question is not 
so much the extent to which a combination of good or bad 
features, or factors of locality, influence tree-growth, but how far 
antagonistic factors go to create neutrality within their limited 
sphere of influence. How far, for instance, does a good soil 
compensate for a bad situation, a wet soil for a dry climate, or a 
sheltered aspect for a windy or exposed district? In answering 
this question, nothing of a very definite nature can be attempted, 
it is true, and everything depends upon the limit which is placed 
upon a choice of species. Apart from conditions which 
