734 RESISTANCE OF FOLIAGE-STEMS TO STRAIN, PRESSURE, AND BENDING. 



tudinally in this way. These proceedings have no disturbing influence on the 

 functions of the vascular bundles, on the conducting power of the wood, or on 

 that of the soft bast, though by the compression of the woody plates the shape 

 of the cross section of the stem is altered. The lateral pressure exerted on the 

 broad side of the plate-shaped vascular bundle is now harmless, and interrupts the 

 transport of the sap neither in the wood nor in the soft bast. 



Fig. 182.— Undulations of old ribbon-shaped liane stems (Bauhinia anguina) from an Indian jungle. 



It has already been shown on p. 477 in one example {Rhynchosia phaseoloides) 

 that injuries due to lateral pressure in the conducting tissues, especially in the 

 soft bast, are also prevented in twining or climbing plants by the development of 

 ribbon-shaped stems, and it need only be added here that with this flattening 

 and ribbon-like shaping of the wood, and with the development of these wings, 

 there is combined an economy of building materials. If the stem were cylindrical, 

 an abundant mechanical tissue would have to be developed for the protection of the 



