MOTION AND SENSITIVENESS IN CLIMBING PLANTS. 59 
C. vitieella it lias spread through the petioles of the several 
leaflets. 
We will conclude our account of leaf-climbers with a short 
notice of Solatium jasminoicles (PL V., figs. 8 and 4). Some 
members of the genus Solanum are twiners ; but this is a true 
leaf-climber. A long shoot made four revolutions, against the 
sun, very regularly at an average rate of 3h. 26m. In no 
other leaf-climber was a leaf grown to its full size capable of 
clasping a stick, though it took several weeks to do it. 
“ When a petiole of a half-grown leaf has clasped a support, in three or four 
days it increases in thickness, and after several weeks becomes hard and rigid. 
On comparing a thin, transverse slice of this petiole with one from the older leaf 
beneath, which had not clasped anything, its diameter was found to be doubled, 
and its structure greatly changed. The sections in fig. 4 will illustrate this 
peculiarity. In that of the petiole in its ordinary state (a) we see a semilunar 
band of cellular tissue, slightly different from that outside it, and including 
three closely approximate groups of dark vessels. Near the upper surface of the 
petiole, beneath two ridges, there are two other small circular groups of vessels. 
In the section of the petiole (b), which had during several weeks clasped a stick, 
the two upper ridges have become much less prominent, and the two groups 
of woody vessels beneath them much increased in diameter. The semilunar 
band is converted into a complete ring of very hard, white, woody tissue, 
with lines radiating from the centre. The three groups of vessels, which, 
though closely approximate, were before distinct, are now completely blended 
together. The upper part of the new ring of woody vessels formed by the 
prolongation of the horns of the original semilunar band is thinner than the 
lower part, and is slightly different in appearance, from being less compact. 
The clasped petiole had actually become thicker than the. stem close beneath ; 
and this was chiefly due to the greater thickness of the ring of wood, which 
presented, both in transverse and longitudinal sections, a closely similar 
structure in the petiole and axis.” 
We must now pass on to— 
III. Tendril Bearers . — True tendrils are formed by the modi- 
fication of leaves with their petioles, of flower-peduncles, and 
perhaps also of branches and stipules. 
Of Bignonia, nine species, taken at hazard, and observed by 
Mr. Darwin, afforded connecting links between twiners, leaf- 
climbers, tendril- bearers, and root-climbers. B. unguis . — 
Young shoots of this species revolve, climbing sometimes in 
different directions. It is a leaf- climber, though possessing 
tendrils. Each leaf consists of a petiole bearing a pair of 
leaflets and terminating in a tendril, a little larger than that 
represented in PI. V., fig. 5, and resembling a bird's foot and 
leg with the hind toe cut off. The toes terminate in sharp 
and hard claws. The main petiole and tendril are alone 
sensitive, the sub-petioles of the leaflets being inert ; hence. 
