168 TENDRIL-BE AKEKS. Chap. IV. 



the twisting of the axis in the one direction is exactly 

 compensated by the twisting in the opposite direction. 

 We can further see how the tendency is given to make 

 the later formed coils oj)posite to those, whether turned 

 to the right or to the left, which are first made. Take 

 a j)iece of string, and let it hang down with the lower 

 end fixed to the floor ; then wind the upper end 

 (holding the string quite loosely) spirally round a per- 

 pendicular pencil, and this will twist the lower part of 

 the string ; and after it has been sufficiently twisted, it 

 will be seen to curve itself into an open spire, with the 

 curves running in an opposite direction to those round 

 the pencil, and consequently with a straight piece of 

 string between the opposed 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 cannot 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 many times as there 

 were coils ; but he winds it into a figure of eight on 

 his thumb and 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 thev take several consecutive turns in 

 one direction and then the same number in an opposite 



