TEXDRIL-BEAKEKS. 99 



than the internodes. In all cases the conditions of life must be 

 favourable for the perfect action of the tendrils. Generally both 

 internodes and tendrils revolve together ; in other cases, as in 

 Cissus, Cobeca, aud most Passiflorae, the tendrils alone revolve ; in 

 other cases, as with Lathyrm aphaca, the internodes alone move, 

 carrying with them the motionless tendrils ; and, lastly (and this 

 is the fourth possible case), neither internodes nor tendrils spon- 

 taneously revolve, as with Lathyrus grandijlorm and the Ampe- 

 lopsis. In most Bignonias, iu the Eccremocarpw, Mutisia, and 

 the Fumariacese, the petioles as well as the tendrils, together with 

 the internodes, all spontaneously move together. 



The tendrils revolve by the curvature of their whole length, 

 excepting the extremity and excepting the base, which parts do 

 not move, or move but little. The movement is of the same nature 

 as that of the revolving internodes. Hence, if a line be painted 

 along that surface which at the time happens to be convex, the 

 line becomes first lateral and then concave, and ultimately again 

 convex. This experiment can be tried only on the thicker ten- 

 drils, which are not affected by a thin crust of dried paint. The 

 extremities, however, of the tendrils, which so often are slightly 

 curved or hooked, never reverse their curvature ; and in this 

 respect they differ from the extremities of the shoots of twining 

 plants, which not only reverse their curvature, or at least become 

 periodically straight, but curve in a greater degree than the lower 

 portions. But, in fact, the tendril answers to the upper intcrnode 

 of the several revolving internodes of a twining plant ; and in 

 the former part of this paper it was explained how the several 

 internodes move together by the whole successively curving to all 

 points of the compass. There is, however, in many cases this 

 unimportant difference, that the curving tendril is separated from 

 the curving internode by a rigid petiole. There is also another 

 difference, namely, that the summit of the shoot, which in itself 

 has no power of revolving, projects above the point from which 

 the tendril arises ; but the summit of the shoot is generally 

 thrown on one side, so as to be out of the way of the revolutions 

 swept by the tendril. In those plants in which the terminal 

 shoot is not sufficiently out of the way, the tendril, as we have 

 seen with the Echinocystis, as soon as it comes in its revolving 

 course to this point, stiffens and straightens itself, and, rising 

 up vertically, passes over the obstacle. 



All tendrils are sensitive, but in very various degrees, to con- 

 tact with any object, and curve towards the touched side. With 



h2 



