240 MOVEMENT IN PLANTS. 



the thicker support become steeper, and thus become 

 closely applied to the thin support ; the younger internodes 

 have continued their growth and have therefore become 

 raised. The older coils do not show this change, because 

 the growth of the older internodes has ended. 



323. Effect of Inversion of Plant on already 

 formed Coils. Take a plant which has made a few coils 

 round a support, turn the pot upside down and support it 

 in this position, and place it in darkness. The younger 

 parts of the stem soon begin to unwind from the support, 

 and the end of the stem directs itself upwards. Clearly 

 this is because each growing zone of the stem has a 

 tendency to grow in a left-handed ascending spiral, so that 

 when the plant is inverted the concave side of the stem 

 (turned towards the support) soon becomes convex, and 

 thus the growing parts become unwound. 



324. Inclined and Horizontal Supports. Try the 



effect of setting the stick in an inclined position, in one 

 pot at 30 from the vertical, in another at 45, in another 

 at 30 above the horizontal, and lay a fourth pot plant 

 horizontally. Note that the Runner, like most other 

 twiners, cannot climb up a stick set at more than 45 from 

 the vertical. 



325. Persistence of Torsion after Disappearance 

 of Coils. Take a pot plant which has made several coils 

 round a stick, and fasten just below its tip a thread which 

 runs over a pulley and carries a small weight, enough to 

 keep the stem from bending over 1 gram will generally 

 do. Make fine ink dots along the stem at short distances 

 from each other. Watch the plant during three or four 

 days, and note that (1) free coils are formed by the upper 

 part of the stem, but these later disappear owing to the 

 straightening of the internodes ; (2) the ink marks are no 

 longer in a straight line, but on a spiral ascending from 

 left to right. The experiment shows (1) that twining is 

 not due to contact, (2) that even when the free coils of the 

 stem disappear with growth the stem still shows torsion. 



