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 



