PROTECTION FROM WINDS. 
^71 
weakness by obeying the laws of health that intelligence teaches 
them, often become stronger at middle age than those of robust 
organization who early waste their vigor by careless disregard of 
those laws. By studying the nature of trees we may effect similar 
results with similar care. 
Winter protection from winds must be effected principally by 
hardy evergreens. Of these the Norway spruce is one of the most 
rapid in its growth. In itself a beautiful object, it may be massed 
in pleasing groups, or compact belts, or close cut colossal hedges. 
The white pine in sandy soils has a still more rapid growth, and 
is, therefore, suited to form the highest screens. The American 
and the Siberian arbor-vitaes are naturally so hedge-like in form 
that the sight of them at once suggests their usefulness j while the 
rambling and graceful young hemlock is readily trained into ver- 
dant screens of exquisite beauty. 
The relative growth of these trees is about in the following 
order : The white pine planted from the nursery should attain the 
height of twenty feet in ten years, and forty feet in twenty years. 
The Norway spruce grows with about the same rapidity, but its 
growth being relatively less in breadth at the top, its summit gives 
less check to winds. The hemlock may attain about two-thirds the 
size of the pine in the same time ; while the arbor-vitaes just named 
may be relied on to make about a foot' of growth per year. These 
facts suggest to intelligent planters the service these trees may be 
made to render in the capacity of protectors of the weaker species 
of trees and shrubs. 
The warming power of evergreen trees in winter is not fully 
appreciated. They are like living beings, breathing all the time, 
and keep up, and give off their vital heat in the same manner. In 
a dense forest the cold is never so intense as on an adjoining 
prairie ; and the difference between the temperature of even a small 
grove of evergreens, and open ground near by, is often great 
enough to decide the life or death of sensitive shrubs and trees. 
In our chapter on the Characteristics of Trees will be found some 
interesting facts concerning this quality of trees and plants. 
Deep drainage, deep culture, and protection from winds are the 
three great means to give trees a healthy and rapid development, 
