CLIMBING PLANTS Ly 
In the shade of hedges the stems become etiolated and 
weak, and the plant climbs. Polygonum dumetorum is 
another imperfect twiner. 
3. Tendril-Climbers.—Tendrils are organs specialized 
for climbing. While growing, they are sensitive to con- 
tact, and their free ends circumnutate. On touching a 
support, the tendril twines round it. The free portion 
between the support and the plant then takes on a spiral 
twist, a reversal-point naturally occurring in the middle, 
since both ends are fixed and incapable of movement 
(Fig. 36). The object of this is to bring the stem closer to 
its support, and at the same time to increase the strength 
Fic. 34.—Convolvulus (BINDWEED), Fia. 35.— Hop, Twintna CLocK- 
TWINING COUNTER - CLOCKWISE. WISE. (REDUCED.) 
(REDUCED. ) 
of the anchoring cable. The closer. the plant is to its 
support and the stronger the cable, the less liable is it 
to be wrenched away from it by the wind and damaged. 
When twining has ceased, the tendril thickens and 
becomes woody, thus making the connection permanent 
and durable. 
The hooks and bristles of scrambling plants are oppor- 
tune outgrowths from the surface of the plant. They are 
neither leaves, roots, nor shoots. Tendrils, on the other 
hand, represent definite plant-organs—leaves or portions 
of leaves, stem-structures, or even roots. We mean by 
this that the rudiment of the tendril started as one of 
