RESISTANCE OF FOLIAGE-STEMS TO STKAIN, I'UKSSURE, AND BENDING. 



rni 



projections from the bast tube, e.g. in the grass Molinia coerulea (fig. 179*), or as 

 iiideponilent colli'uchyiiiatous strands in the corners of the antfnlar stem, as in the 

 \Voo<irurt"(-'-l>''i't'C((.ia odorata, fig. 179*), or, again, a circle of independent bundles of 

 hard bast appeara outside the bast tube, as in the stately umbellifer Euryangium 

 Sumbul (fig. 179'). In this plant the strengthening accessories are combined into 

 independent simple girdere and a canal filled witli air is situated on the inner side 

 of each of the llanges {cf. fig. 179"). 



The third group consists of all stems in which the flanges ai-e developed as 



V: 



Fig. 180,— Transverse sections of erect foliage-stems with flanges developed as secondary giiduis. 



' Tufttd Scirpus (Scirpus ccespilosus). 2 Perfoliate Silphium (.WpAtumptr/oiuid/jn). •Black-stemmed Bamboo (Bamhusa 

 nigra). * Hard Rush (Juncm glaucus). 6 Common Reed (Fhragmites communis). * Sugar-cane {Saccharum offtcinanim). 

 In these diagrammatic figures the mechauicul tissue is represented grey, and the vascular bundles black with white spots. 



secondary girders. Tlie web in these secondary girders always consists of vascular 

 bundles, and the flanges themselves of hard bast. Sometimes the secondary gii-ders 

 are arranged in a single circle, but in most instances they foi'm several concentric 

 rings. In fig. 180 some of the most striking forms of this gi-oup are given diagram- 

 maticciUy. Fig. ISO "^ represents a transverse section of a stem of Scirpus cws- 

 pitosrxs, in which the secondary girdei-s — arranged in a single circle — alternate with 

 large air-spaces; fig. 180^ shows a similar section of the stem of the composite illus- 

 trated on p. 239 {Silphium jyerfoliatum), with its numerous series of secondary 

 girders parallel to the four sides; and fig. 180^ is the transvei'se section of a bamboo 

 {Bawhusa nigra) in which the secondary girders are grouped in several concentric 

 rings. Here, as in the first and second groups, accessory structures are present, 



