Roots: their Structure and Grotrth. 77 



the water in such cases through their leaves, but they give it 

 out to the air where it most needs it, if there be crops under cul- 

 tivation, and besides strengthening the banks, they shade the sur- 

 face from the sun and winds. The roots of willows afford tlu> best 

 prevention against erosion of banks, in light soils, and these and 

 other trees and plants most effectually hold in place embankments, 

 and sands liable to drift by the winds. 



273. The smaller roots of trees are covered, especially near their 

 extremities, by radicles or fibers, through which the water in the soil, 

 and various mineral elements in solution, arc- taken up and conveyed 

 in the form of sap to the leaves, by passing up among the pores of 

 the wood. The vigor of growth in a tree is generally proportioned 

 to the abundance of its radicles, and success in planting depends 

 upon their preservation to as great an extent as possible without 

 drying. 



274. Roots will often form buds and produce leaves, when ex- 

 posed to the air, and in many species buds will form roots when 

 buried as layers while still attached to the tree. In the mistletoe 

 and other parasites, the roots will penetrate the wood of living trees 

 upon which their viscid seeds get attached, thus weakening the vi- 

 tality of the trees to which the}- fasten, by absorbing their juices. 



275. In some cases the roots, and especially their bark, possess 

 medicinal properties, often due to an essential oil, as in the sassa- 

 fras. These qualities are generally more abundant in trees grown 

 in hot climates, and become less in the same species where they will 

 bear transplanting to cooler latitudes. 



276. In rare cases, the roots of different trees of the same species 

 will grow together under ground, so that when one is cut down its 

 stump will continue to live, and even to increase slightly in size, 

 from the nourishment it derives from the other tree. But where from 

 close proximity trees of different species have their roots so closely 

 interlocked that are apparently united as one, it will be found upon 

 a cross-section that there is a line of bark or distinct separation be- 

 tween them. 



277. In some cases, a fungus growth will attach to the root, and 

 spreading from one tree to another, cause their destruction, the in- 

 fection extending from a center in a circular form. This is most ef- 

 fectually arrested by digging trenches deeper than the roots reach, 



