While discussing these descriptions, a brief explanation of plant-structure may be given. In treating this subject, the teacher must govern himself by the needs of his class, and the means at his command. Explanations requiring the use of a compound microscope do not enter necessarily into these lessons. The object aimed at is to teach the pupils about the things which they can see and handle for themselves. Looking at sections that others have prepared is like looking at pictures; and, while useful in opening their eyes and minds to the wonders hidden from our unassisted sight, fails to give the real benefit of scientific training. Plants are built up of cells. The delicate-walled spherical, or polygonal, cells which make up the bulk of an herbaceous stem, constitute cellular tissue (_parenchyma_). This was well seen in the stem of the cutting of Bean in which the roots had begun to form.[1] The strengthening fabric in almost all flowering plants is made up of woody bundles, or woody tissue.[2] The wood-cells are cells which are elongated and with thickened walls. There are many kinds of them. Those where the walls are very thick and the cavity within extremely small are _fibres_. A kind of cell, not strictly woody, is where many cells form long vessels by the breaking away of the connecting walls. These are _ducts_. These two kinds of cells are generally associated together in woody bundles, called therefore fibro-vascular bundles. We have already spoken of them as making the dots on the leaf-scars, and forming the strengthening fabric of the leaves.[3] [Footnote 1: See page 46.] [Footnote 2: If elements of the same kind are untied, they constitute a tissue to which is given the name of those elements; thus parenchyma cells form parenchyma tissue or simply parenchyma; cork-cells form cork, etc. A tissue can therefore be defined as a fabric of united cells which have had a common origin and obeyed a common law of growth.--Physiological Botany. p. 102.] [Footnote 3: See page 58.]