Guourbita maxima and C. Pepo. 55 



the bands of growth still continue to act in the basal portion, 

 and still tend to bow the tendril alternately in all directions. 

 Their power to do so is necessarily modified by fixation of the 

 tip, and the natural result would be for the base to pass by the 

 support as a curve, with the sensitive side outermost, and then 

 develop torsion. These changes we find to occur from the be- 

 ginning. If the coiling were primarily due to irritation, then 

 we should expect to find the coil first developed as the result 

 of simple contraction on one side, and this would not immedi- 

 ately give rise to torsion. The spiral formed in one direction 

 after a time reverses itself as a natural result of excessive 

 torsion in one direction, as Darwin has already proved,* and 

 there is thus completed a double spiral spring, which draws 

 more and more closely, becomes hard and woody after a time, 

 and holds the plant to a strong but elastic support. How use- 

 ful this arrangement is, may be readily seen during a strong 

 wind when, under its influence, the plant is forced this way 

 and that, in danger of being torn and broken. The springs 

 then yield just enough to relieve the strain and avoid the possi- 

 bility of danger. It was frequently noticed that, while corn 

 and other plants offering much resistance to strong winds, were 

 torn badly, the squash always came out whole. 



During its active period, the tendril arm elongates rapidly, 

 and the cessation of movement and of growth in length are 

 simultaneous. From a series of measurements made, the fol- 

 lowing data were obtained. An arm just uncoiled from the bud 

 measured 12 cm in length. One day later it had increased to 

 14'8 cm , and on the following day to 18 •S ™, thus giving a total 

 increase in length of 6'3 om , or one-half its original length. 

 August 8th, five tendrils but a short time in action, were care- 

 fully measured and marked. The Monday following, 10th, all 

 except one were found to have coiled about themselves or other 

 objects. The coils were drawn out as fully as possible and 

 measurements taken, but even then, the full length could not be 

 obtained. The measurements were as follows : 



No. 1. No. 2. No. 3. No. 4. No. 5. 



August 8th, 12- om 12-4 17'7 10*4 17'5 



August 10th, 24*5 19-0+ 25-0+ 20*5+ 33'0 + 



Gain,... 12-5 6-6 7:3 10-1 ]5'5 



Add for coils, . _ 1-0 3-0 o'O 1-0 



Total gain, 12-5 7'6 10-3 15-1 16-5 



Thus we find, the extreme range in elongation to be from 

 one-half of to the same length as the tendril when it first 



* Climbing Plants, p. 163. 



