268 EFFECT ON SEMI-TROPICAL TREES. 
ness. These must first be provided with the bottom heat that 
deep drainage and a well-aired subsoil provides, until they are 
deeply rooted. 
As newly planted trees have not the means of keeping them- 
selves warm in winter by means of their deep roots, it follows that 
they must be nursed in some way so that they will maintain a 
vigorous life until they are thus provided. 
Trees or shrubs of half-tropical habit, by which we mean those 
that flourish in our southern States without protection, and which 
may be so carefully managed as to develop their beauties healthily 
in the northern States, of course need this careful nursing more 
than any other ; and not only to guard them against winter’s ex- 
cesses, but to give them the most equable ground temperature at 
all seasons. Most trees in their native localities grow in deep 
shades, and the soil over their roots is rarely heated by the direct 
rays of the sun, however powerful its heat upon their tops. The 
very luxuriance of vegetation forms a bower of shade for the 
soil ; so that in forests the roots of trees are in a soil that is com- 
paratively equable in temperature and moisture. When trees from 
such localities are grown on open lawns, they are naturally dis- 
posed to branch low, in order to cover their roots from the heat of 
the summer sun by the shade of their own boughs. The mag- 
nolias and rhododendrons are marked examples of trees and 
shrubs which .are cultivated most successfully in deeply drained 
soils, but at the same time are ill-at-ease in ground where the soil 
over their roots is bared to the scorching summer heat. In the 
case of evergreen trees, their low-branching keeps the ground under 
them cool and shady in summer, and also protects the roots in 
winter — acting as a blanket to hold the radiation of the earth’s 
heat, and to hold the snow which makes another blanket for the 
same purpose. A well-cut lawn is some protection to the roots of 
trees, but it interferes with that active oxygenation of the soil which 
deep culture produces ; and while it acts as a shield against the 
scorching effect of the summer sun on bare earth, and as a mulch to 
counteract, in a slight degree, the rapid changes of temperature on 
the surface-roots, it at the same time reduces the vitality and power 
of resistance to cold in the tree, by preventing the deep soil from 
