MOVEMENT IN PLANTS. 231 



with reference to the stem, and tie the stem to a vertical 

 stick. Place the plants in darkness, A laid horizontally, 

 B at an angle of 45 above the horizon, C at 45 below 

 the horizon, and D upside down. After several days note 

 any changes in the direction of growth of the branches. 



304. Diageotropism in Leaves. Tie the stem of a 

 potted plant to a vertical stick, secure the soil against 

 falling out, invert the pot, and keep the plant in darkness 

 for several days. Note how the leaves move into the 

 normal position; the petiole or base of the leaf -blade 

 usually curves so as to turn the tip of the blade towards 

 the stem, but this inward curvature is followed by a twist- 

 ing movement if the petiole is very short or absent, only 

 the twisting movement (geo-torsion) occurs. 



305. Diageotropism and other Orientation Move- 

 ments in Flowers. (a) Take four specimens of a single- 

 flowered Narcissus in which the perianth tube is horizontal 

 and at right angles to the flowering stem. Cut off each 

 flowering stem a few inches below the flower, and stick it 

 through the bored cork of a test-tube filled with water. 

 Fix the four tubes so that the perianth-tube of A faces 

 vertically downwards ; that of B at 45 above the horizon ; 

 that of C 45 below the horizon; that of D vertically 

 upwards. In which of the four does the flower- stalk 

 curve so as to bring the perianth-tube into the horizontal 

 position ? 



(6) Bend down the inflorescence of Monkshood (the 

 plant should be dug up and placed in a flower-pot, set in 

 darkness during the experiment) so that the terminal 

 portion with its flower-buds points vertically downwards, 

 and secure it in this position. Note that the stalk of each 

 flower curves upwards so as to bring the hood- sepal once 

 more uppermost. But this bending movement causes the 

 flower to face the axis of the inflorescence, and the flower- 

 stalk now undergoes torsion so that the flower comes to 

 face outwards. The first movement (bending) is geotropic, 

 Tbut the second (twisting) is evidently autonomous. 



