238 MOVEMENT IN PLANTS. 



place and then in a cold place, or vice versa. At 33 C. a 

 Runner plant revolved in 2 hours 20 minutes, while at 

 24 C. the plant took 3 hours 25 minutes to revolve. 



317. Influence of Light Direction on Rate of Movement. 

 Place the plant near a window, so that the plane of curvature of the 

 upper part is at right angles to that of the window, and the shoot 

 tip faces you. Note that the movement towards the light (the 

 first half of the revolution) is more rapid than that away from the 

 light (the second half of the revolution). 



318. Revolution causes Twisting of Stem. Mark 

 an ink line along the convex side of the stern, and watch 

 what happens during a revolution ; place the plant as in 

 the preceding experiment. If the shoot tip faces north to 

 begin with, at quarter revolution it will face west and the 

 ink line will be on the left side of the stem ; therefore the 

 zone of most active growth (indicated by the convex side) 

 has shifted 90 to the right, while the stem tip has 

 described a horizontal arc of 90 to the left. At half 

 revolution, the line will be on the concave side of the stem, 

 and so on until, when the revolution is complete, it regains 

 its original position, and has then described a spiral. 



319. Tightening of Coils around Support. Place a 

 vertical stick near the plant in one of the pots. Note that 

 the revolving stem on touching the stick begins to revolve 

 in a narrower circle, twining round the stick. Later, the 

 coils become more closely applied to the stick, also 

 becoming steeper. The twining stem continues to grow 

 for some time after coiling; it cannot straighten itself 

 completely, because of the support which stands in the 

 way, but this growth tightens the clasp of the stem on the 

 support. 



320. Free Coiling of Stem-tip. Examine a vigorous 

 Runner plant growing in the open, and note that the shoot 

 tips which happen to project beyond the support do not 

 show distinct spiral coils. Cut off several of these free 

 tips, about 5 cm. long, as nearly straight as possible, and 

 set each in a test-tube of water, placing the tubes in a 



