6 HooKER: PHYSIOLOGICAL OBSERVATIONS 
two weeks, during which time their glands secrete actively. At 
the end of this period the tentacle begins to bend backward. In 
old leaves the marginal tentacles are much recurved, and in 
extreme cases the gland may pass through a complete revolution 
by the rolling up of the distal portion of the pedicel. The petiole 
of young leaves pointsup. As the leaf ages, its petiole bends down 
so that the mature leaf is horizontal. 
The pedicels of the exterior tentacles are dorsi-ventrally 
flattened at the base. The abaxial side has numerous short 
glandular hairs distributed over its entire length. On the adaxial 
side they are fewer in number and are confined more or less to 
- the base. 
(b) EXPERIMENTAL METHOD 
Fresh leaves which had not been previously touched were 
selected for experimentation. The entire plant was removed from 
the Sphagnum in which it grew and was placed in a large Stender 
dish. A piece of cork was fastened with sealing wax inside the 
dish and another piece attached to it by two pins. The petiole 
of the selected leaf was clamped horizontally between the two 
pieces of cork in such a way that the leaf-blade was vertical. 
The bottom of the dish was covered with water and the roots were 
wrapped in wet sphagnum. The cover of the Stender dish was 
replaced or discarded, as desired. A binocular microscope was 
used, because the greater distance from the objective to the 
object made it more convenient when the Stender dish was 
covered. An horizontal tentacle, which showed glandular hairs 
on both upper and lower sides and which was not obscured by its 
neighbors, was selected from the edge of the leaf opposite the 
petiole. Its pedicel was marked with China ink to facilitate 
identification. 
Each tentacle was measured with a micrometer scale and drawn 
with a camera lucida before an experiment. The gland was then 
stimulated by placing upon it some object such as the leg of a fly. 
This was removed as soon as movement began. At each subse- 
quent observation the time was recorded and the tentacle was 
sketched. This was continued at intervals until the pedicel was 
again straight. The tentacle was then measured for the second 
time with the micrometer scale. 
