STEMS 



655 



fall of a tendril climber; the stems of woody twiners bometimes are 

 ruptured by the increasing pressure to which they are subjected by 

 the diametral enlargement of the tree, though more commonly the 

 twining stem becomes embedded in the growing trunk. 



The origin and distribution of lianas. While herbaceous lianas 



FIG. 966. A grape-vine (Vitis) that has clambered over a hawthorn (Crataegus) 

 and occasioned its destruction; in the left foreground is a cotton wood (Populus deltoides) 

 and in the left background is an elm (Ulmus amencana) ; River Forest. 111. Photograph 

 by LAND. 



may occur almost anywhere, woody lianas are associated peculiarly with 

 forests, reaching their culmination in the tropics, where there exist all 

 but impenetrable tangles of intertwining vines, some of which (as the 

 rattan palm) may reach the great length of 250 meters, that is, equal 

 to twice the height of the tallest trees (fig. 967). In temperate regions 

 lianas culminate in the rich soil along rivers, the greenbrier thickets with 



