126 Alpine Plants. 
that is needed is shelter against the force ot strong 
winds, and their drying or cutting influence. The 
means of shelter may be either environmental or 
integral to the rock-garden, gained from existing 
screens of trees or shrubs, boundary walls or fences, 
or the side of a dwelling-house, supplied by natural 
advantages of slope or inequalities of level in the 
actual site, whether untouched or accentuated, or 
by special provision made close to the rockery itself, 
with its benefit alone in view. It need hardly be 
said that opportunities to turn bank sides or 
inequalities of ground to advantage should be seized 
most keenly and used to the full. But comparatively 
few small rockeries can have a site so freely chosen 
or so favourably disposed as to dispense with direct 
provision for their need of shelter. This may be 
given in either of two ways: by screens of shrubbery 
or by barriers, whether of hedge, fence, or wall. 
Screens of shrubs and trees or of shrubs alone, 
grown upon the outer sides of banks around the 
rockery, except on the south, are the most natural, 
pleasing, and easily treated as well as effective cover, 
but, apart from the initial expense and labour involved 
in their formation, demand more space than can 
often be given; for the rockery must not only be 
perfectly open, it must also be entirely free from 
drip, and from intrusive roots which drain and im- 
poverish the soil. Screens of the same nature, on 
low mounds or on the level, take up less space but 
are less efficient, often permitting draught. In any 
case, adjacent screens of this character should be 
severed from the rockery itself by a considerable 
