ROOTS AS CONDUCTORS OF HEAT. 267 
true and so useful. Now if we can keep the plants’ feet warm and 
dry, or at least save them from the greatest extremes of cold and 
wet, we do them the same kindness that we do the children by 
wrapping their feet in wool and leather protections. 
The roots of trees and shrubs during the first five years of their 
growth are mostly in that part of the soil which is frozen in the 
northern States from one to three feet deep every winter. Some 
rapid-growing trees, as the yellow locust and the silver poplar, 
send down their roots to a great depth very soon after planting. 
We have seen roots of the locust that had penetrated a marly clay 
and were as large as pipe-stems at a depth of six feet below the 
surface, from trees only three years planted. This power of quick 
and deep rooting in the subsoil is probably the reason why the 
locust tree, with its tropical luxuriance and extreme delicacy of 
foliage, is able to endure a degree of cold that many less succulent 
and hardier looking trees cannot bear. 
Deep Roots as Conductors of Heat to the Tops of 
Trees. —The deep roots have an influence in maintaining an 
equilibrium of temperature in the tree that is little understood. 
They are direct conductors from the even warmth of the unfrozen 
subsoil, to the trunk and branches which are battling with frigid 
air, and winds that strive to rob them of their vital heat. All 
winter long this current of heat is conducted by the deep roots to 
the exposed top. The greater the cold, the greater the call on 
these roots to maintain the equilibrium; and consequently their 
usefulness in this respect is in proportion to the extremes of tem¬ 
perature above ground which the tree may be required to resist, 
and the proportion of roots which are below the frost-line. Surface 
roots are the summer-feeding roots—multiplying their myriads of 
fibres, each one a greedy mouth, when spring opens and the leaves 
need them;—and there is always a perfect proportion between their 
abundance and vigor, and the luxuriance of the foliage above them. 
Surface manuring promotes a rank growth of these roots, and of 
the foliage; and should only be used for young trees and shrubs 
which are unquestionably hardy, or for the less hardy which are 
already deeply rooted; but not for young trees of doubtful hardi- 
