652 



ECOLOGY 



FIGS. 958-960. 958, tendrils of a 

 wild cucumber (Echinocystis lobata); 

 note the reverse directions of the spirals, 

 those at t being dextrorse and those at t' 

 sinistrorse; note also the coiling of the tendril ends about the support; 959, 960, tendrils 

 of Cobaea scandens: 959, a compound leaf with three pairs of leaflets and a terminal 

 dichotomously branched tendril; 960, the tip of one of the tendril branches considerably 

 magnified, showing the recurved hooks which hold the plant to a support. 



the lower part of a coil appears at the right and the upper part disappears at the 

 left, the twiner is called dextrorse (as in the hop). Common native twiners are the 

 bittersweet (Celastrus) and the dodder (Cuscuta), the latter being a parasite in which 



contact stimulation incites the develop- 

 ment of sucking organs (haustoria) that 

 serve also to hold the climber firmly to 

 ' the supporting plant. In twiners and 



in other lianas there is a striking 

 development of conductive tissues 

 (p. 689). 



FIGS. 961-963. Tendrils of the Japan 

 ivy (Psedera tricuspidata): 961, a portion of 

 a stem, showing a young tendril (/), the 

 branches having small globular swellings (s) 

 at the tipj 962, a similar tendril at maturity, 

 the swollen tips (s 1 ) being much larger, and 

 also flattened on the side in contact with the 

 support; 963, a mature tendril tip, somewhat 

 magnified, showing the adhesive disk (d), 

 which may fasten even to a smooth surface. 



Tendril climbers. Scarcely 

 second to twiners in specializa- 

 tion are the tendril climbers, the 

 tendril commonly being an organ 

 homologous with leaves or leaflets 

 (figs. 959, 960, 939, 943), or with 

 branches (as in the passion flowers 

 and grapes, figs. 961, 962); or 

 tendrils may be organs of doubt- 

 ful homology (as in the pumpkin 



