48 » LEAF-CLIMBERS. Cuar. II. 
position, which is preserved ever afterwards. The 
petioles which have clasped any object soon become 
much thickened and strengthened, as may be seen 
in the drawing. 
Clematis montana.—The long, thin petioles of the 
leaves, whilst young, are sensitive, and when lightly 
rubbed bend to the rubbed side, subsequently becom- 
ing straight. They are far more sensitive than the 
petioles of C. glandulosa ; for a loop of thread weighing 
a quarter of a grain (16°2 mg.) caused them to bend; 
a loop weighing only one-eighth of a grain (8:1 mg.) 
sometimes acted and sometimes did not act. The 
sensitiveness extends from the blade of the leaf to 
the stem. I may here state that I ascertained in 
all cases the weights of the string and thread used 
by carefully weighing 50 inches in a chemical balance, 
and then cutting off measured lengths. The main 
petiole carries three leaflets; but their short, sub- 
petioles are not sensitive. A young, inclined shoot 
(the plant being im the greenhouse) made a large 
circle opposed to the course of the sun in 4 hrs. 20 m., 
but the next day, being very cold, the time was 
5hrs.10m. A stick placed near a revolving stem was 
soon struck by the petioles which stand out at right 
angles, and the revolving movement was thus arrested. 
The petioles then began, being excited by the contact, 
to slowly wind round the stick. When the stick was 
thin, a petiole sometimes wound twice round it. 
The opposite leaf was in no way affected. The atti- 
tude assumed by the stem after the petiole had 
