304 THE BIOLOGY OF FLOWERING PLANTS 

 air, and often cover their foster parent with blossom not its 



own." 



The lianas form the subject of an exhaustive study by 

 Schenck (1892), from the details of which it appears that 

 each type of climber we have described reaches its highest 

 perfection, greatest variety in detail, and most exaggerated 

 expression in the tropics. An interesting structural feature 

 with a mechanical bearing may be mentioned. The 

 twiners are, as we have said, twisted on their own axes as 

 well as wound round the support. This, combined with 

 the unilateral pressure against the support, leads to most 

 remarkable anomalies in the secondary thickening of woody 

 forms. The wood is never continuous. The necessary 

 pliability is attained most simply by the wood being split 

 up into wedges which may be again lobed or cleft. In 

 other cases, it occurs in isolated clumps. The cambium 

 is sometimes renewed many times outwards in the cortex 

 so that a series of concentric zones of wood separated by 

 rings of ground tissue is produced. As the stem is often 

 narrowly elliptical in section these wood bands may be only 

 arcs of a circle. Finally, the stem may be deeply cleft 

 into rounded segments, each with its own cylinder of wood. 

 The approach to the structure of cordage composed of 

 separate twisted strands is, in such cases, very remarkable. 

 The great length of the internodes may be noted. The 

 vessels of the tropical Uanas are the longest and widest 

 known ; this is related to water transport to great heights 

 through a narrow stem (Fig. 47). 



Into further details we cannot go ; descriptions may be 

 found in Schimper and Warming, and in the works of 

 Schenck and Haberlandt already quoted . We may conclude 

 this account by a quotation from Haberlandt, the descrip- 

 tion of a rambling palm, which, with some bamboos, may 

 be taken as the highest type of rambler, *' ... the cHmbing 

 or Rotang palms, which have neither twining stems nor 

 sensitive tendrils, v/hich nevertheless mount to the tops of 

 the highest trees in the thickets of the primeval forest, and, 

 thrusting above the foliage of the wood, let their glittering 



