The tree, as we have indicated, gets its food from the air and the soil. The rootlets have the power of dissolving the mineral salts in the soil in which they ramify; some authorities believing that they are materially helped in this respect--so far as organic matter is concerned--by a fungus that invests them with a mantle of delicate threads. However that may be, the fluid that is taken up by the roots is not merely water, but water plus dissolved mineral matter and nitrogen. At the same time as the roots are thus absorbing liquid nutriment, the leaves, pierced with thousands of little _stomata_, or mouths, take in atmospheric air, which is compounded chiefly of the gases oxygen and carbon. The leaf-cells containing the green colouring matter (_chlorophyll_) seize hold of the carbon and release the oxygen. The carbon is then combined with the fluid from the roots by the vital chemistry of the leaves, and is circulated all over the system for the sustenance of all the organs and tissues. The flowering of the trees varies so greatly that it can only be dealt with satisfactorily as each species is described. It may be stated, however, that all the true forest trees are wind-fertilized, and therefore have inconspicuous greenish blossoms. By true forest trees we mean those that alone or slightly mixed are capable of forming high forest. The smaller trees, such as Crab, Rowan, Cherry, Blackthorn, Hawthorn, Buckthorn, etc., belong more to the open woodland, to the common and the hedgerow. These, from their habitat, can be seen singly, and therefore can make use of the conspicuous flowers that are fertilized by insects. WAYSIDE AND WOODLAND TREES. PART I. NATIVE TREES AND SHRUBS. The Oak (_Quercus robur_). When good John Evelyn wrote his "Sylva, or a Discourse of Forest Trees," he was greatly concerned lest our "wooden walls" should diminish in strength for want of a succession of stout Oaks in our woodlands, and therefore he put the Oak in the forefront of his discourse. To-day steel and teak have largely supplanted oak in the building of our navy, and our walls of defence are no longer of wood. Yet in spite of these changes, and the consequent reduction of the Oak's importance, we must still look upon it as the typical British tree, and, regardless of its place in botanical classifications, we shall follow the lead of our master and place it first on our list.