58 LEAF-CLIMBERS. Cuap. TI. 
length of about one-eighth of an inch of a sub-petiole, 
was lightly rubbed with the same twig only once; it 
became slightly curved in 3 hrs., remaining so during 
Il hrs., but by the next morning was quite straight. 
The following observations are more precise. After 
trying heavier pieces of string and thread, I placed a 
loop of fine string, weighing 1-04 gr. (67-4 mg.) on a 
terminal sub-petiole: in 6 hrs. 40 m. a curvature could 
be seen; in 24 hrs, the petiole formed an open ring round 
the string ; in 48 hrs. the ring had almost closed on the 
string, and in 72 hrs. seized it so firmly, that some 
force was necessary for its withdrawal. <A loop weighing 
2 of a grain (383°7 mg.) caused in 14 hrs. a lateral sub- 
petiole just perceptibly to curve, and in 24 hrs. it 
moved through ninety degrees. These observations were 
made during the summer: the following were made . 
in the spring, when the petioles apparently are more 
sensitive :—A loop of thread, weighing one-eighth of a 
grain (8:01 mg.), produced no effect on the lateral sub- 
petioles, but placed on a terminal one, caused it, after 
24 hrs., to curve moderately ; the curvature, though the 
loop remained suspended, was after 48 hrs. diminished, 
but never disappeared; showing that the petiole had 
become partially accustomed to the insufficient stimulus. 
This experiment was twice. repeated with nearly the 
same result. Lastly, a loop of thread, weighing only 
one-sixteenth of a grain (4:05 mg.) was twice gently 
placed by a forceps on a terminal sub-petiole (the 
plant being, of course, in a still and closed room), and 
this weight certainly caused a flexure, which very 
