132 Alpine Plants. 
the varying conditions of humidity or drought that 
prevail at the extremes of winter and summer, and 
to secure a deep root-run that shall remain equable 
in its conditions of moisture and temperature at all 
times; indeed, the construction as well as the 
planning of a rockery are as much indicated by the 
necessity to provide against temporal changes of 
climatic condition as against the steady sway of its 
extremes of dryness or moisture. 
To further these objects the mound should rise in 
successive, more or less rounded, terraces until the 
main broad, elevated plateau of the rockery is 
reached. These terraces should descend in successive 
planes towards the south or south and east until they 
cease about 6in. from the ground, forming there the 
outlines of the bed, the main aspect of the whole being 
towards the south or towards the south-east, which is 
on the whole the better aspect in most cases, provided 
it is available without difficulty. The surface of each 
terrace should dip slightly down towards the base of 
the next terrace above. It is best to keep a fairly 
wide terrace round the margins at the base of the 
rockery for smaller stuff, devoting portions of this 
here and there to a shelf-like disposition of the 
rockwork—after the fashion of the steps in a tilted- 
back step-ladder—filled with earth. 
The steep and contracted ledges thus obtained form 
an admirable site for such dwarf and choice species 
as Potentilla nitida, Armeria czspitosa, etc. In 
planning the rockery it is best to provide a more or 
less extensive low and long mound in front of the 
chief area on which to grow sheets or cushions of such 
