. Comparative anatomy of the vegetative organs of the phanerogams and ferns. Plant anatomy; Phanerogams; Ferns. i6o the lumen (comp. Figs. 59-60). The cavity of the pit is in most cases originally and often permanently of the form of a plano-convex lens (' half-lens-shaped'), since the outer surface of the thickening of the membrane, which borders it on one side, is concave, while the unthickened portion of the membrane, which limits it on the other, is flat. The canal is, according to the extent of the thickening of the membrane, either extremely short, so that a sharp-edged openin
. Comparative anatomy of the vegetative organs of the phanerogams and ferns. Plant anatomy; Phanerogams; Ferns. i6o the lumen (comp. Figs. 59-60). The cavity of the pit is in most cases originally and often permanently of the form of a plano-convex lens (' half-lens-shaped'), since the outer surface of the thickening of the membrane, which borders it on one side, is concave, while the unthickened portion of the membrane, which limits it on the other, is flat. The canal is, according to the extent of the thickening of the membrane, either extremely short, so that a sharp-edged opening leads from the lumen of the tube into the cavity of the pit, e. g. in the thin-walled tracheides of the spring wood of Pinus ; or, when the thickening is greater, it is elongated, and widens outwards suddenly into the cavity of the pit, e. g. autumn w'ood of Pinus, pitted vessels of Nerium, Fraxinus, wood-elements of Convolvulus Cneorum, Pteris aquilina (Figs. 61, 64), &c. The above general description of the structure of the bordered pit is said to hold for those uncommon bordered pits, not belonging to our present subject, which occur in certain ce/ls ^, and for those on the limiting surfaces between Tracheae and other elements; and it is clear that between these and the non-bordered pits only the above-described difference of form exists, which corresponds exactly to that between the flattened and the |— shaped fibrous thickenings. On the surfaces abutting on elements of another order, the bordered pits of the Tracheae either correspond to non-bordered pits on the walls of these, or they are opposite to an unpitted wall. But where Tracheae with bordered pits are contiguous with one another, the bordered pits correspond to one another in such a way, that on each limiting surface all the cavities of the pits of the one fit exactly over those of the other. The plano-convex cavities are thus applied to one another in pairs, so as to form the ' lens-shaped pit-cavities '
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Keywords: ., bookcentury1800, bookdecad, booksubjectplantanatomy, bookyear1884
