Experiment 4.—­A large fragment of a fly was placed on a leaf, in a medial line, a little beneath the apex.  Both lateral margins were perceptibly incurved in 3 hrs., and after 4 hrs. 20 m. to such a degree that the fragment was clasped by both margins.  After 24 hrs. the two infolded edges near the apex (for the lower part of the leaf was not at all affected) were measured and found to be .11 of an inch (2.795 mm.) apart.  The fly was now removed, and a stream of water poured over the leaf so as to wash the surface; and after 24 hrs. the margins were .25 of an inch (6.349 mm.) apart, so that they were largely unfolded.  After an additional 24 hrs. they were completely unfolded.  Another fly was now put on the same spot to see whether this leaf, on which the first fly had been left 24 hrs., would move again; after 10 hrs. there was a trace of incurvation, but this did not increase during the next 24 hrs.  A bit of meat was also placed on the margin of a leaf, which four days previously had become strongly incurved over a fragment of a fly and had afterwards re-expanded; but the meat did not cause even a trace of incurvation.  On the contrary, the margin became somewhat reflexed, as if injured, and so remained for the three following days, as long as it was observed.

Experiment 5.—­A large fragment of a fly was placed halfway between the apex and base of a leaf and halfway between the midrib and one margin.  A short space of this margin, opposite the fly, showed a trace of incurvation after 3 hrs., and this became strongly pronounced in 7 hrs.  After 24 hrs. the infolded edge was only .16 of an inch (4.064 mm.) from the midrib.  The margin now began to unfold, though the fly was left on the leaf; so that by the next morning (i.e. 48 hrs. from the time when the fly was first put on) the infolded edge had almost completely recovered its original position, being now .3 of an inch (7.62 mm.), instead of .16 of an inch, from the midrib.  A trace of flexure was, however, still visible.

Experiment 6.—­A young and concave leaf was selected with its margins slightly and naturally incurved.  Two rather large, oblong, rectangular pieces of roast meat were placed with their ends touching the infolded edge, and .46 of an inch (11.68 mm.) [page 373] apart from one another.  After 24 hrs. the margin was greatly and equally incurved (see fig. 16) throughout this space, and for a length of .12 or .13 of an inch (3.048 or 3.302 mm.) above and below each bit; so that the margin had been affected over a greater length between the two bits, owing to their conjoint action, than beyond them.  The bits of meat were too large to be clasped by the margin, but they were tilted up, one of them so as to stand almost vertically.  After 48 hrs. the margin was almost unfolded, and the bits had sunk down.  When again examined after two days, the margin was quite unfolded, with the exception of the naturally inflected edge; and one of the bits of meat, the end of which had at first touched the edge, was now .067 of an inch (1.70 mm.) distant from it; so that this bit had been pushed thus far across the blade of the leaf.