116 BRITISH PLANTS 
from those of prostrate habit. The latter may easily, if 
circumstances favour, become scramblers. True scram- 
blers, however, are provided with special organs to aid — 
them—hooks, prickles, barbs, or recurved bristles. These 
grappling structures are not to be associated with the 
sensitive climbing organs of true climbers, for they are 
not sensitive to contact, and have no movements of their 
own. The bramble or blackberry (Rubus fruticosus) and 
the dog-rose (Rosa canina) are provided with large re- 
curved “hooks, which arise as emergences upon the stems 
and leaves. In the moss-rose and Rosa spinosissima the 
emergences are straight, and not fitted for climbing ; they 
serve only for defence. The goosegrass, or cleavers 
(Galium Aparine), scrambles up the hedges by its rough 
stems and leaves, which are armed with a multitude of 
small reflexed bristles. . 
2. Twiners.—The weak stems of these plants twine 
round supports, provided that these are not too thick 
nor too smooth. The growing tips are sensitive, and 
describe slowly and regularly circles or ellipses. This 
spontaneous movement is known as “ circumnutation ” 
(Lat. corcum, around ; nuto, I nod). In the black bryony 
(Tamus communis) the apex describes one complete revolu- 
tion in about two and a half hours. By means of these 
movements the stem is enabled to come into contact with 
supports which it otherwise would fail to reach. On 
reaching the support, the stem twines round it. Some 
plants twine clockwise, others counter-clockwise, but for 
every plant the direction is fixed, the habit having 
become hereditary. 
(a) Twiners climbing counter-clockwise, the usual 
habit: Phaseolus vulgaris (scarlet runner), Wistaria 
chinensis, Convolvulus sepium (Fig. 34), Polygonum Convol- 
vulus, Cuscuta (dodder, Fig. 42). 
(6) Twiners climbing clockwise: Humulus Luwpulus 
(hop, Fig. 35), Tamus communis (black bryony), Lonicera 
(honeysuckle). 
Wistaria and hop connect this group with the scram- 
blers, the former having recurved spiny stipules, and the 
latter T-shaped stiff hairs. 
Solanum Dulcamara (woody nightshade) is a feeble 
climber, and may climb either way. In the open, where 
the light is strong, it is a low bush, not climbing at all. 
