CH. XIV] THE CLIMBERS 575 



as mechanical support. Both habitats and vegetation forms 

 merge off gradually from those already described, beginning 

 with the simpler autophytic mesophytic climbers, and 

 passing through all gradations to extreme parasites. They 

 include plants from all of the four great divisions, Thallo- 

 phytes to Spermatophytes. Accordingly we recognize, 



A. THE HABITATS OCCUPIED BY CLIMBERS, OR LIANES. 



B. THE HABITATS OCCUPIED BY EPIPHYTES. 



C. THE HABITATS OCCUPIED BY HALF-PARASITES. 



D. THE HABITATS OCCUPIED BY PARASITES AND SAPROPHYTES. 



E. THE HABIT OF THE INSECTIVOROUS PLANTS. 



A. THE HABITATS OCCUPIED BYLIMBERS, _QR 



The erect self-supporting trunks built by trees for the 

 spread of their own foliage, offer opportunity to other plants 

 to achieve the elevation of their foliage without themselves 

 providing stout stems; and correspondingly we have the 

 extstence^of many forms of slender-stemmed climbers or 

 lianes, which are specially abundant in tropical forests. 

 Their stems are largely composed of grea/^ducts, and they 

 possess always some definite method whereby they are 

 enabled to .cling to their support. The principal vegetation 

 forms are the following. 



CLAMBERING VINES ; very slender, often branched, cling- 

 ing haphazard to large vegetation by aid of retrorse hooks, 

 etc., as in Rattan Palm (Fig. 376), a form very common in 

 the tropics. Such are our Bedstraws (Galium) in miniature, 

 and our Clematis, though with hooks replaced by sensitive 

 petioles (Fig. 51). TWINING VINES; these turn spirally 

 around the support, as in Morning Glory, Climbing Bitter- 

 sweet, and many tropical lianes, the latter often choking 

 the support plant. CLINGING VINES ; with thigmotropically 

 sensitive tendrils, as in Grape Vines, and Passion Vines 

 (Fig. 136). Allied are the tropical forms with horizontal 

 climbing roots (Fig. 181), including climbing Aroids. AD- 

 HERENT VINES; with clinging disks at the tips of aerial 



