TWINERS AND CLIMBERS. 213 



attached to a smooth board. The discs are generally 

 formed on one side of the curved tip, and never, as 

 far as yet observed, without coming in contact with 

 some object.^ Dr. McNab- has observed in another 

 species that small globose discs are formed before the 

 tips come into contact. This also corresponds with 

 the observations on Bignonia. 



It seems evident that these discs possess the power 

 of secreting some resinous cement, by means of 

 which they adhere to the support to which they 

 attach themselves. When a tendril does not become 

 attached, its primary object being frustrated, in the 

 course pf a few weeks it shrinks and withers, and 

 finally drops off When the discs have become 

 attached, then the tendril contracts spirally, so as to 

 become very elastic, and at the same time thickens 

 so as to attain increased strength. Even after the 

 tendrils are dead they still continue to adhere, and 

 retain strength. One single branch of a tendril, 

 which had been dead at least for ten years, still 

 remained elastic, and capable of supporting a weight 

 of two pounds, so that assuming all the branches 

 of the same tendril to have been equally attached, 

 and equally strong, the entire tendril would be 

 capable of enduring a strain of ten pounds. Sachs 



^ Darwin, " Movements of Climbing Plants," p. 145. 

 2 Dr. McNab, in "Transactions of Botanical Society, Edin- 

 burgh," xi., p. 292. 



