TWINERS AND CLIMBERS. 207 



large circular sweeps were observed within an hour 

 and a quarter, but the growing point does not rotate. 

 In Echinocystis lobata, a plant of the cucumber family, 

 the tendrils, which are from seven to nine inches in 

 length, revolve as well as the internodes, but over 

 a wider surface. The circles swept by the tendrils 

 are from fifteen to sixteen inches in diameter, whilst 

 those of the internodes are not more than about three 

 inches. The quickest rate of motion for the comple- 

 tion of a revolution was about one hour and three- 

 quarters. 1 In a passion-flower the internodes as well 

 as the tendrils rotate, the former very rapidly, per- 

 forming its revolution in an average period of about 

 an hour. In a species of trumpet-flower (Bignonia 

 littoralis) the mature tendrils rotate much slower than 

 the internodes, the former taking six hours to per- 

 form a revolution, and the latter two hours and 

 three-quarters. In the Virginia creeper neither the 

 internodes nor the tendrils possess the power of 

 rotation. 



That tendrils are sensitive to a touch, one might 

 expect from the purposes they are called upon to 

 serve, but this faculty varies in different species. In 

 one of the passion-flowers (Passiflora gracilis) where 

 the tendrils are thin, delicate, and straight, except 

 the curved tips, a single delicate touch on the concave 



1 Darwin, " Movement of Climbing Plants," p. 128. 



