. Notes on the life history of British flowering plants. Botany; Plant ecology. 38 BRITISH FLOWERING PLANTS 1 1 1 1 ! 1 1 1 1 1 Fig. 23 gii d -Single er. Fig. 24.—Double girder. cally called. This need not be so strong as the flanges. It has not the same force to resist, and may be a lattice or open work. The applications of these principles in architecture has led to the well-known " girder " (see Fig. 23), in which the material is collected in two more or less thin flanges united by a narrow rib. In some sub- stances—in cast iron, for instance—as Mr. Hodgkinson has shown,^ the resi
. Notes on the life history of British flowering plants. Botany; Plant ecology. 38 BRITISH FLOWERING PLANTS 1 1 1 1 ! 1 1 1 1 1 Fig. 23 gii d -Single er. Fig. 24.—Double girder. cally called. This need not be so strong as the flanges. It has not the same force to resist, and may be a lattice or open work. The applications of these principles in architecture has led to the well-known " girder " (see Fig. 23), in which the material is collected in two more or less thin flanges united by a narrow rib. In some sub- stances—in cast iron, for instance—as Mr. Hodgkinson has shown,^ the resistance to compression is much greater than the resistance to extension, and in the strongest girder, therefore, the greater flange may be on the extended side. If the forces to be resisted act in two directions at right angles to one another, two girders must be combined, as in Fig. 24. If the forces come in all directions, a series of girders would be required (Fig. 25). This is the case in the stems of trees (see Fig. 26). Now in the stems of plants the strength is given by tissues known as hard bast, libriform cells, or scleren- chyma, which are collectively termed, in ordinary language, woody fibres. The hard bast of some plants equals steel in its power of resistance. Hence its use for string, ropes, etc. The " web " consists of vas- cular bundles and parenchymatous cells. Here strength is not required. In some cases—for instance, in many Grasses— the centre is hollow. If the mechanical or woody tissue formed a pillar in the centre of the stem, there would evidently be a great waste of strength (see Fig. 25). An erect stem which is liable to wind pressure, some- times from one side and sometimes from another, must be strengthened in all directions. Hence a series of ^ Mem, Manchester Phil. Soc. vol. FiQ. 25.—Multiple Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability
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