INTRODUCTION 



is remarkable, and generally springing from the upper side, running in such 

 directions as to give the branches a horizontal appearance. The spray of the 

 Ash runs in a scries of irregular parallels, the shoots springing out in opposite 

 pairs, often only one coining to maturity, and that usually on the under side, 

 so as to form elegant pendent houghs. In the Elm we find spray forming a 

 series of acute angles with the parent branch, being given off" on alternate 

 sides, often becoming pendent with age. The Beech exhibits the same kind 

 of altcrnacy, but the acute angles are smaller, the distance between the twigs 

 is wider, and the whole runs a kind of zigzag course, becoming pendent, but 

 twisted and entangled. The subject may be pursued in other trees, but 

 enough has been said to show that much may be learned towards recognising 

 the species even in the leafless stage. 



MAIN STEM OR TRUNK 



The main stem or trunk of the tree is also in many instances peculiarly 

 characteristic, as we may see in the leaden-grey, smooth trunk of the Beech, 

 the peculiarly twisted stem of the Sweet Chestnut, or the rough, red-brown 

 trunk of the Scots Fir, so frequently bent over near the top and denuded of 

 its lower branches. 



THE BARK AND ITS USES 



The bark also serves very largely as a distinguishing mark, as in the 

 thick, deeply furrowed, corky bark of the Oak, the shallower grooves in the 

 Ash, the silvery-white peeling layers of the Birch, or the flaking plates of 

 the Planes. The outer bark of trees is usually dead and dry, and in many 

 cases is corky, giving a rugged appearance to the stem, as in the Elm and 

 Oak, whilst in others it is capable of great distension, and presents a smooth 

 appearance, as in the Beech. It is a protective tissue, acting as a buffer to 

 the soft delicate structures that lie beneath, and one of its chief uses is to 

 prevent excessive evaporation of the cell sap. 



In the bark of stem and branches we may often observe small transpira- 

 tion pores known as lenticels. They assume characteristic forms according to 



vi 



