98 :MB. D.VUWIN ON CLIMBING PLANTS. 



tion to those round the pencil, and consequently with a straight 

 piece of string between the opposite spires. In short, we have 

 given to the string the regular spiral arrangement of a tendril 

 caught at both ends. The spiral contraction generally begins at 

 the extremity which has clasped a support ; and these first-formed 

 spires give a twist to the axis of the tendril, which necessarily 

 inclines the basal part into an opposite spiral curvature. I can- 

 not resist giving one other illustration, though superfluous : when 

 a haberdasher winds up ribbon for a customer, he does not wind 

 it into a single coil ; for, if he did, the ribbon would twist itself as 

 manv times as there were coils ; but he winds it into a figure of 

 eight on his thumb aud little finger, so that he alternately takes 

 turns in opposite directions, and thus the ribbon is not twisted. 

 So it is with tendrils, with this sole difference, that they take 

 several consecutive turns in one direction and then the same 

 number in an opposite direction ; but in both cases the self-twist- 

 ing is equally avoided. 



Summary on the Nature and Action of Tendrils. — In the con- 

 cluding remarks I shall have to allude to some points which may 

 be here passed over. In the majority of tendril-bearing genera 

 the young interuodes revolve in more or less broad ellipses, like 

 those made by twiuing plants ; but the figures described, when 

 carefully traced, generally form irregular ellipsoidal spires. . The 

 rate of revolution in different plants varies from one to five hours, 

 and consequently in some cases is more rapid than with any 

 twining plant, and is never so slow as with those many twiners, 

 which take more than five hours for each revolution. The direc- 

 tion is variable even in the same individual plant. In Passijlora, 

 the internodes of only one of the species have the power of re- 

 volving. The Vine is the weakest revolver observed by me, appa- 

 rently exhibiting only a trace of a former power. In the Eccremo- 

 carpus the movement is interrupted by many long pauses. Some, 

 but very few, tendril-bearing plants can spirally twine up an up- 

 right stick. Although the twining-power has generally been lost 

 by tendril-bearers, cither from the stiffness or shortness of the 

 internodes, from the size of the leaves, or from other unknown 

 causes, the revolving movement well serves to bring the tendrils 

 into contact with surrounding objects. 



The tendrils also have the power of revolving in the same manner 

 and generally at the same rate with the internodes. The move- 

 ment begins'whilst the tendril is young, but is at first slow. In 

 Bignonia littoralis even the mature tendrils moved much slower 



