ROOTS AS CONDUCTORS OF HEAT. 367 



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 a^-^--:- 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- 



