With iron then, a cane, I suppose, will strike fire very easily? MRS. B. I understand that it will. --In ever-greens the epidermis is mostly resinous, and in some few plants is formed of wax. The resin, from its want of affinity for water, tends to preserve the plant from the destructive effects of violent rains, severe climates, or inclement seasons, to which this species of vegetables is peculiarly exposed. EMILY. Resin must preserve wood just like a varnish, as it is the essential ingredient of varnishes? MRS. B. Yes; and by this means it prevents likewise all unnecessary expenditure of moisture. The parenchyma is immediately beneath the epidermis; it is that green rind which appears when you strip a branch of any tree or shrub of its external coat of bark. The parenchyma is not confined to the stem or branches, but extends over every part of the plant. It forms the green matter of the leaves, and is composed of tubes filled with a peculiar juice. The cortical layers are immediately in contact with the wood; they abound with tannin and gallic acid, and consist of small vessels through which the sap descends after being elaborated in the leaves. The cortical layers are annually renewed, the old bark being converted into wood. EMILY. But through what vessels does the sap ascend? MRS. B. That function is performed by the tubes of the alburnum, or wood, which is immediately beneath the cortical layers. The wood is composed of woody fibre, mucilage, and resin. The fibres are disposed in two ways; some of them longitudinally, and these form what is called the silver grain of the wood. The others, which are concentric, are called the spurious grain. These last are disposed in layers, from the number of which the age of the tree may be computed, a new one being produced annually by the conversion of the bark into wood. The oldest, and consequently most internal part of the alburnum, is called heart-wood; it appears to be dead, at least no vital functions are discernible in it. It is through the tubes of the living alburnum that the sap rises. These, therefore, spread into the leaves, and there communicate with the extremities of the vessels of the cortical layers, into which they pour their contents. CAROLINE. Of what use, then, are the tubes of the parenchyma, since neither the ascending nor descending sap passes through them? MRS. B.