. Botany for young people and common schools. How plants grow, a simple introduction to structural botany. With a popular flora, or an arrangement and description of common plants, both wild and cultivated. Botany. KINDS AND rORMS OF LEAVES. 43. '(;ii|.'iii(iillii17/M,Sv::-''lif; 'il:!! liii i!iiiii:!iil!:i!^.U^l Exogenous Stems. SI of Flax-stem inagnifiGd; and al-o in Fig. 81, -wlilcli shows the same structure in a woody stem, namely, in a shoot of Maple of a year old, cut both crosswise and len2;thwise. 116. The difference becomes still more marked in stems more than one year old. During the
. Botany for young people and common schools. How plants grow, a simple introduction to structural botany. With a popular flora, or an arrangement and description of common plants, both wild and cultivated. Botany. KINDS AND rORMS OF LEAVES. 43. '(;ii|.'iii(iillii17/M,Sv::-''lif; 'il:!! liii i!iiiii:!iil!:i!^.U^l Exogenous Stems. SI of Flax-stem inagnifiGd; and al-o in Fig. 81, -wlilcli shows the same structure in a woody stem, namely, in a shoot of Maple of a year old, cut both crosswise and len2;thwise. 116. The difference becomes still more marked in stems more than one year old. During the second year a new layer of wood is formed outside of the first one, between it and the bark; the third year, another laA'cr outside of the second, and so on, a new layer being formed each year outside of that of the year before. The increase is all on the surface, and buries the older wood deeper and deeper in the trunk. For this reason such stems are said to be exogenoi's or outside-growing (from two Greek words which mean just this), a new layer being added to the wood on the outside each year as long as the tree or shrub lives. And zo the oldest wood, or Heart-wood^ is always in the centre, and the newest and freshest, the Sap-wood^ at the circumference, just beneath the bark. 117. The heart-wood is dead, or soon becomes fo. The sap-wood is the only active part; and this, with the inner bark, which is renewed from its inner face eveiy year, is all of the trunk that is concerned in the life and growth of the tree. 118. Plants with exogenous or outside-growing stems, especially those that live year after year, almost always branch freely. All common shrubs and trees of the exogenous class make a new set of branches every year, and so present an ap- pearance very different from that of mo3t of those of the endogenous or inside- growing class. § 3. Of Leaves. 119. Leaves exhibit an almost endless variety of forms in different plants; and their forms afford easy marks for disti
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