SPECIAL FOUMS. 



55 



the figure. 1 The tendrils of Virginia Creeper (Fig. 93) are of the 

 same nature and position. But, instead of laying hold \)y a coiling 

 of the tip, when it has reached any solid surface, such as a wall 

 or tree-trunk, the tip expands into an adhesive disc, which forms 

 a secure attachment. (Fig. 94.) In a related plant, Vitis (Cissus) 

 tricuspidata of Japan, these disks terminate the branches of very 

 short tendrils : consequently the shoots as they grow are at 

 once applied closely and secured firmly to the surface of the sup- 

 port, an admirable adaptation for climbing walls and trunks. 



111. The simple tendril of a Passion- 

 flower, being in the axil of a leaf (that 

 is in the position of a branch) , is also of 

 axial nature : it is a leafless and simple 

 branch, composed of one long and slen- 

 der internode, devoted to the purpose of 

 climbing. Fig. 95 shows in all stages the 

 admirably active tendrils of Passiflora 

 sicyoides. This is a Mexican species, 

 remarkable for the rapidity and freedom 

 with which the tendrils move. The lowest 

 tendril in the figure is attached and 

 coiled : the next is free and coiled in 

 one helix : the third is outstretched 

 and seeking a support. For tendrils 

 which are not homologous with stems, 

 see Sect. IV. 228. 

 112. A Spine or Thorn (Fig. 96, 97) is usually a branch or 

 the termination of a stem or branch, indurated, leafless, and 

 attenuated to a point. The nature of spines is manifest in the 

 Hawthorn (Fig. 97), not only by their position in the axil of a 

 leaf, but often by producing imperfect leaves and buds. And 

 in the Sloe, Pear, &c., many of the stinted branches become 

 spinose or spntescent at the apex, tapering off gradually into a 

 rigid and leafless point, thus exhibiting ever}' gradation between a 



spine and an ordinary branch. These spinose branches are less 



. 



1 This forms what is called a Sympodinm or Sijmpodial stem, which is mor- 

 phologically made up of a series of superposed brandies. (Sec Chapter V. __ 

 281,282.) In contradistinction, a stem formed hy the continued development /"* /S~ 

 of a terminal bud is Monopodial or a Monopodium. Fig. 95 is an example. 



FIG. 95. Leafy slioot of Passiflora sicyoides, of Mexico, with fixed and coiled, free 

 uiiil full grown, and forming tendrils. 



