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. 



