$2 LEAF-CLIMBERS. ; Cuar. IL. 
stiff petioles of Clematis flammula are sensitive to everi 
much less weight if spread over a wide surface. The 
petioles always bend towards the side which is pressed 
or touched, at different rates in different species, 
sometimes within a few minutes, but generally after 
auch longer period. After temporary contact with 
any object, the petiole continues to bend for a con- - 
siderable time; afterwards it slowly becomes straight 
again, and can then re-act. A petiole excited by an 
extremely slight weight sometimes bends a little, and 
then becomes accustomed to the stimulus, and either 
bends no more or becomes straight again, the weight 
still remaining suspended. Petioles which have clasped 
an object for some little time cannot recover their 
original position. After remaining clasped for two or 
three days, they generally increase much in thickness 
either throughout their whole diameter or on one side 
alone; they subsequently become stronger and more 
woody, sometimes to a wonderful degree ; and in some 
cases they acquire an internal structure like that of the 
stem or axis. - : 
The young internodes of the Lophospermum as well 
as the petioles are sensitive to a touch, and by their 
combined movement seize an object. The flower- 
peduncles of the Maurandia semperflorens revolve 
- spontaneously and are sensitive to a touch, yet are not 
used for climbing. The leaves of at least two, and 
probably of most, of the species of Clematis, of Fumaria 
and Adlumia, spontaneously curve from side to side, 
like the internodes, and are thus better adapted to 
