. Botany of the living plant. Botany. 152 BOTANY UF THE LIVING PLANT. I'lG. no. Transverse section of stem of Laiiniiin, showing projecting angles of colien- cfiyma (dotted), opposite four larger vascular strands : an arrangement equi- \'alent to two crossed girders. ( â : r4.) The central tissue mav even of the large number of the strands, and their slight irregularities ; and this is common in herbaceous Dicotyledons. But in the case of Clematis only three crossed girders enter into the construction,so that the method appears clearer : and still more so in Lamium, where there are only
. Botany of the living plant. Botany. 152 BOTANY UF THE LIVING PLANT. I'lG. no. Transverse section of stem of Laiiniiin, showing projecting angles of colien- cfiyma (dotted), opposite four larger vascular strands : an arrangement equi- \'alent to two crossed girders. ( â : r4.) The central tissue mav even of the large number of the strands, and their slight irregularities ; and this is common in herbaceous Dicotyledons. But in the case of Clematis only three crossed girders enter into the construction,so that the method appears clearer : and still more so in Lamium, where there are only two. There are other points of wide apj lication illustrated in these cases. The stems are fluted, with projecting angles, and one strap of mechanical tissue is seated in each. This gives added strength on the principle of the fluted column, the depth of each girder being thereby increased. The second point is that one of the stronger vascular strands is opposite each of the mechanically strengthened lidges, so that the construction of the stem, as it grows older and the vascular strands become mechanically more effective, resembles that of a number of peripheral girders disposed in a ring. This method is seen in the fraines supporting large gasometers, be replaced by a cavity fihed with air, which gives added point to the comparison. The simpler construction of the stem in Lamium may be compared mechanically with that of a lattice signal post. In it four bauds of metal occupy the four angles, and are kept in place by a lattice- work of thin straps, while the centre is hollow. So in Lammm (Fig. no), the projecting angles contain the chief mechanical tissue The softer tissues hold them in place, while there is a central pith-cavity It is immateiial exactly how the mechanical arrange- ments are analysed in such stems as these quoted. The point is that the girder principle can be recognised in them all, with strengthening strands isolated and peripheral. But in Dico- tyledons the
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1919
