MOVEMENT IN PLANTS. 229 



299. Apogeotropism in Grass "Nodes." In the 



stems of most plants the power of apogeotropic curvature 

 is confined to the uppermost internodes, but in Grasses 

 the tissue in the swollen " nodes " (really the swollen 

 bases of the leaf-sheaths) remains capable of growth- 

 curvature for a long tim e , after the internodes have 

 become mature and rigid. Cut from the flowering stem 

 of Eye, Barley, or other Cereal or Grass, a number of 

 pieces about 10 cm. long, each with a " node " at the 

 middle, and set them in order side by side, horizontally, 

 in the sand box. After a day note that the pieces have 

 curved upwards, the younger pieces curving more 

 vigorously than the older ones. The free internode above 

 the node remains straight; curvature is confined to the 

 node itself. 



300. Measurement of Curvature (Grass " Nodes "). 



Cut a piece of Grass stem with a node, and mark the 

 latter on two opposite sides with an ink line or dot at 

 each end of the node, measuring the distance between 

 the two marks (say 2 to 3 mm.). Stick the piece hori- 

 zontally, so that one of the marked sides is above and the 

 other below. After a day, when the node has bent, 

 measure again, and note that the lower side of the node 

 has grown greatly in length, while the upper side has 

 shortened. 



301. "After-effect." (1) Fit a Bean-shoot into a 

 bottle or tube of water, using a bored or split cork and 

 sealing with plasticine, and let the shoot project hori- 

 zontally. Stick a pin or needle into the free end of the 

 shoot and set up beside it a foot-rule ; note the position 

 of the index-pin on the scale. After half an hour (the 

 shoot will have made little or no upward movement in that 

 time) turn the bottle round through 180, taking care to 

 keep the free end at the same point on the scale. The 

 shoot soon begins to curve downwards, then it comes to 

 rest, and finally it curves upwards showing that there is 

 an interval between (1) the perception of the stimulus and 

 (2) the visible response made by the shoot. 



