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 aire 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 points up. 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. 



