Cuap. II. CLEMATIS. 51 
thick as the opposite one which has clasped nothing. 
When thin transverse slices of the two are placed 
under the microscope their difference is conspicuous: 
the side of the petiole which has been in contact with 
the support, is formed of a layer of colourless cells with 
their longer axes directed from the centre, and these 
are very much larger than the corresponding cells 
in the opposite or unchanged petiole; the central 
cells, also, are in some degree enlarged, and the whole 
is much indurated. The exterior surface generally 
becomes bright red. But a far greater change takes 
place in the nature of the tissues than that which is 
visible: the petiole of the unclasped leaf is flexible 
and can be snapped easily, whereas the clasped one 
acquires an. extraordinary degree of toughness and 
rigidity, so that considerable force is required to pull 
it into pieces. “With this change, great durability is 
probably acquired ; at least this is the case with the 
clasped petioles of Clematis vitalba. The meaning of 
these changes is obvious, namely, that the petioles may 
firmly and durably support the stem. 
Clematis microphylla, var. leptophylla—The long 
and thin internodes of this Australian species revolve 
sometimes in one direction and sometimes in an op- 
posite one, describing long, narrow, irregular ellipses 
or large circles. Four revolutions were completed 
within five minutes of the same average rate of 
1 hr. 51m.; so that this species moves more quickly 
than the others of the genus. The shoots, when placed 
near a vertical stick, either twine round it, or clasp it 
