TWINING OF TENDRILS. 
865 
sap. The direct action of light is not necessary for twining, since even etiolated plants 
(as Ipomcea purpurea and Phaseolus multiflorus) cling closely to their support in the dark. 
The assertion of Duchartre that Dioscorea Batatas does not twine in the dark reduces 
itself, according to de Vries's more recent observations, to the fact that while normal 
green shoots continue to climb in the dark, they cease rotating and twining when they 
become etiolated. 
Sect. 25. — The Twining of Tendrils^. Under the term tendril may be 
comprised all filiform or at least slender long and narrow parts of plants which 
possess the property of curving round slender solid supports with which they come 
in contact during their growth, cHnging to them in consequence, and thus at length 
fixing the plant to them. Tendrils are therefore at once distinguished from climbing 
internodes by their irritabihty to contact or pressure. 
Organs of the most various morphological description may assume this physi- 
ological property. Sometimes tendrils are metamorphosed branches, as in ViiiSf 
Ampelopsi's, Passiflora, and Cardiospermum Halicacabum, where they may be con- 
sidered more accurately as metamorphosed flower-stalks or inflorescences. In 
Cuscuta the whole stem may be regarded as a tendril rather than as a climbing 
stem. In other cases, as in Clematis, TropcBolum (Fig. 486), Maurandia, Lopho- 
spermum, Solanum jasminoides, &c., the petioles may serve as tendrils. In Fu- 
maria officinalis and Corydalis claviculata the whole of the finely-divided leaf is 
sensitive to contact, and its separate parts have the power of twining round slender 
bodies. In Gloriosa Plantii and Flagellaria indica the mid-rib protruding beyond 
the leaf serves as a tendril. In many Bignoniaceae, in Cobcea scandens, in Pisum^ 
&c. the anterior (upper) part of the pinnate leaf is transformed into slender fiUform 
tendrils inclined forwards, while the basal part of the leaf is rigid and divided 
into leaflets j sometimes, as in Lathyrus Aphaca, the whole of the leaf is replaced 
by a fiHform tendril. The morphological character of the tendrils of Cucurbi- 
taceae is still doubtful, though they must probably be regarded as metamorphosed 
branches. 
Fig. 486. — Mode of climbing of Tropceohim minus. The long petiole a of the leaf / is sensitive to 
long-continued contact, and has clung round a support and round the stem of the plant itself st so as to 
fix this stem firmly to the support ; z the shoot from the axil of the leaf 
^ See the literature quoted in the preceding section, and de Vries, Arb. d. bot, Inst, in 
Würzburg, I. 
3 K 
