170 TENDRIL-BEARERS. Cuap. IV. 
the internodes and tendrils revolve together at the 
same rate; in Cissus, Cobaa, and most Passiflore, the 
tendrils alone revolve; in other cases, as with Lathyrus 
aphaca, only the internodes move, carrying with them 
the motionless tendrils; and, lastly (and this is the 
fourth possible case), neither internodes nor tendrils 
spontaneously revolve, as with Lathyrus grandiflorus 
and Ampelopsis. In most Bignonias, Eccremocarpus, 
Mutisia, and the Fumariacez, the internodes, petioles 
and tendrils all move harmoniously together. In 
every case the conditions of life must be favourable in 
order that the different parts should act in a perfect 
manner. 
Tendrils revolve by the curvature of their whole 
length, excepting the sensitive extremity and the 
base, which parts do not move, or move but little. 
The movement is of the same nature as that of the 
revolving internodes, and, from the observations of 
Sachs and H. de Vries, no doubt is due to the same 
cause, namely, the rapid growth of a longitudinal band, 
which travels round the tendril and successively bows 
each part to the opposite side. Hence, if a line be 
painted along that surface which happens at the time 
to be convex, the line becomes first lateral, then 
concave, then lateral, and ultimately again convex. 
This experiment can be tried only on the thicker 
tendrils, which are not affected by a thin crust of 
dried paint. The extremities are often slightly curved 
or hooked, and the curvature of this part is never 
reversed; in this respect they differ from the ex- 
