118 BRITISH PLANTS 
these organs, but in the course of its development it 
became modified as a climbing organ, and gradually 
assumed the form and functions of a tendril. 
The Morphology of Tendrils—(a) Modified Stem or 
Shoot Structures.—These generally occur in the posi- 
tion of flowering shoots, and so may be regarded as 
modified floral branches. Their morphological nature 
may be established from the fact that they arise in 
the axils of leaves (passion-flower, Fig. 36), or them- 
selves bear leaves or the vestiges of leaves, or even 
Fic. 36.—Passion-FLowER. (REDUCED.) 
a, branch-tendril with reversal-point at b ; c, extra-floral nectary ; d, vegeta- 
tive bud ; e, flower-bud ; /, stipule. 
flowers (vine). They may be branched (vine) or un- 
branched (passion-flower.) In the virginia-creeper, Am- 
pelopsis Vertchit (Vitis inconstans or Veitchii), each branch 
of the tendril bears at its tip a small adhesive pad, which 
cements the tendril to the wall (Fig. 37). 
(>) Modified Leaves or Parts of Leaves—(i.) Leaflets.— 
In peas (Lathyrus) and vetches (Vicia) some of the ter- 
minal leaflets are modified into tendrils. In the ever- 
lasting pea all but two leaflets are modified, and the stem 
becomes winged and green (Fig. 38). In Lathyrus A phaca 
every leaflet becomes a tendril, and the work of assimila- 
