Climbing Plants 245 
tendril contracts spirally, and by so doing it draws 
up the branch upon which it grows. Coiled thus, 
it is as elastic as a steel spring, and when the main 
stalk of the tendril is pulled the strain is distrib- 
uted equally among all the attached disks. With- 
ered branches of the Virginia creeper continue to 
cling to their supporting wall years after their 
death, despite the tugging winds of many winters 
and the softening influences of the rains of many 
springs. Darwin experimented upon a single lateral 
branchlet of a tendril supposed to be at least ten 
years old, and found that it supported a weight 
of two pounds. ‘‘The whole tendril had five disk- 
bearing branches, of equal thickness, and appar- 
ently of equal strength, so that, after having been 
exposed during ten years to the weather, it would 
probably have resisted a strain of ten pounds.” 
But a tendril which has found no support un- 
dergoes no further development. It was ‘‘ adapted” 
to catch and cling, and as it has failed to fulfil 
its office there is no further use for it in the vine’s 
economy. For, whatever society may do, Nature 
tolerates no shirks. The useless tendril, in the 
course of a week or two, shrivels into a slender 
thread, drops off, and drifts away like summer 
leaves in October. 
