410 CLIMBING PLANTS. 
caught between the stem and the petiole as by a pair of 
pincers. The internode straightens itself again, excepting 
the part in contact with the stick. 
With Solanum jasminoides (Fig. 88) as in no other leaf- 
climber examined, a leaf grown to its full size was capable 
of clasping a stick ; but the movement was extremely slow, 
requiring several weeks. On comparing a thin transverse 
Fig. 88. slice of this petiole with 
one from the next or older 
leaf beneath, which had not 
clasped anything, its diam- 
eter was found to be fully 
doubled, and its structure 
greatly changed. In the 
section of the petiole 
which had during several 
weeks clasped a stick, the 
two upper ridges have be- 
come much less prominent, 
and the two groups of 
woody vessels beneath 
Molanum Macalasddes, 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 com- 
pletely blended together. This clasped petiole had actually 
become thicker than the stem close beneath; due chiefly to 
the greater thickness of the ring of wood. 
Plants belonging to eight families are known to have 
clasping petioles, and plants belonging to four families climb 
by the tips of their leaves. With rare exceptions the peti- 
oles are sensitive only whilst young; they are sensitive on 
all sides, but in different degrees in different plants. 
Tendril-bearing Plants. — By tendrils are meant fila- 
mentary organs, sensitive to contact and used exclusively 
