THE STEM 169 
leaves (Fig. 69) or are of doubt- 
ful homology, as in the squash 
family (Fig. 166). Tendrils are 
long, slender structures which 
coil around other objects or, 
more rarely, bear disks which 
adhere to the surface of the 
support. 
Root climbers. Many climbers 
adhere to a support by means of 
- numerous small roots which de- 
velop from the stem (Fig. 179). 
Scramblers. Climbers of this 
type are not so definitely fas- 
tened to their support as are those 
of the othertypes. They are held 
up more loosely by means of 
thorns (Fig. 163) or hooks (Fig. 
162). Climbing roses and rasp- 
berries are examples of thorn 
scramblers. Hooks are more ad- 
vantageous than thorns, as they 
have a greater tendency to keep 
a plant from slipping backward. 
The thorns or hooks may be stem 
(Figs. 162, 163) or leaf struc- 
tures. Rattans are excellent ex- 
amples of scramblers with hooks 
on the leaves (Fig. 70). 
Photosynthesis (leaf function). 
The young stems of green plants 
contain chlorophyll and carry on 
photosynthesis to some extent, 
while herbaceous stems continue 




Fig. 168. Flattened stem of Mueh- 
lenbeckia platyclada specialized for 
photosynthesis. (x }) 

Fie. 169. Leaflike branches of Phyl- 
locladus protractus. (x #) 
to perform this function as long as they live. All green stems, 
therefore, perform to some extent the function which is the 
