MECHANISMS FOR CONVEYANCE TO AND FRO. 475 



protection against lateral pressure are also found in creepers and climbing planta 

 with perennial woody stems, and in those plants which are commonly called lianes. 

 In order to comprehend these contrivances rightly, it is necessary first to get an 

 idea of the position of the parts requiring protection in perennial woody plants. 



Fig. 127. — RhynchoBia pliaseotoides, a Liane with ribbon-like Stems. 



which neither climb nor creep, and which possess an erect, straight, column-like 

 trunk. As previously stated, in these plants to which belong the firs, oaks, beeches, 

 elms, limes, apple-trees, and, generally, the majority of leafy trees, the vascular 

 bundles are arranged in a ring round the central pith, and consist essentially 

 of the woody portion, serving to conduct the raw sap, and the bast portion, which 

 is employed in the transmission and transformations of the organic substances 

 formed in the green cells. These two portions are separated in the plants men- 



