2 TWINING PLANTS. Cua. I, 
I believe that my observations, founded on the ex- 
amination of above a hundred widely distinct living 
species, contain sufficient novelty to justify me in 
publishing them. 
Climbing plants may be divided into four classes. 
First, those which twine spirally round a support, and 
are not aided by any other movement. Secondly, 
those endowed with irritable organs, which when they 
touch any object clasp it; such organs consisting of 
modified leaves, branches, or flower-peduncles. But 
these two classes sometimes graduate to a certain 
extent into one another. Plants of the third class 
ascend merely by the aid of hooks; and those of the 
fourth by rootlets; but as in neither class do the plants 
exhibit any special movements, they present little 
interest, and generally when I speak of climbing plants 
I refer to the two first great classes. 
Twininc PLANTS. 
This is the largest subdivision, and is apparently 
the primordial and simplest condition of the class. 
My observations will be best given by taking a few 
special cases. When the shoot of a Hop (Humulus 
lupulus) rises from the ground, the two or three first- 
formed joints or internodes are straight and remain 
stationary; but the next-formed, whilst very young, 
spontanés,” &c.,‘ComptesRendus,”  cherches sur la Volubilité des 
tom. xvii. (1843) p. 989; “Re- Tiges,” &c., tom. xix. (1844) p. 295. 
