42 THE BOOK OF GARDEN DESIGN 
hills, it would be waste of opportunity not to do so. 
As the outline of boundary plantations will in many 
cases cut the horizon, leaving the tops of the trees show- 
ing clear against a background of sky, great attention 
should be paid to making this outline as attractive as 
possible. It is a mistake to use trees of only one 
kind, as this results in a level monotonous outline any- 
thing but pleasing. The tall spire of a} poplar will 
give variety and point to a plantation composed almost 
entirely of trees with rounded heads; a graceful birch 
with its feathery outline would break the level of a 
smooth belt of shrubs. Colour too is all important, a 
judicious mixture of evergreen and deciduous trees is 
generally preferable to a plantation composed entirely 
of one class. There is no need to make the boundary 
plantation straight on the inner side, whatever may be 
required on the outer, and the formation of well marked 
swells and bays will lend an air of charm and indefinite- 
ness. It is usual to plant trees of large growth on 
rising ground, reserving dwarf varieties and bushes for 
the hollows, but this is a rule which must be modified 
according to circumstances. By a continuous system of 
grouping the eye may be carried from the garden 
itself to the very outskirts of the property, and this 
is much more satisfactory than the plan of treating the 
outer plantation as a mere fence, quite independent of 
what may lie within it. 
The indiscriminate dotting of specimen trees about 
a park or garden is much overdone, and in the greater 
number of cases irregular groups of trees having some- 
what similar characteristics would be far more satis- 
factory. Certain trees, as the tulip tree, and the wych 
elm, are well adapted for isolation on the lawn, and are 
welcome for the shade they afford; but thorns, the 
flowering crabs, and the Scotch firs should always be 
planted in groups. As these smaller plantations are 
