Cuourbita maxima and 0. Pepo. 53 



Irritation on the upper side, near the tip, produces a curvature 

 through the central region of the arm, with the concavity 

 uppermost, showing in this, a distinct transmission of the im- 

 pulse to somewhat remote parts. A sharp blow on the upper 

 surface, as with a pencil, throws the arm into a series of long 

 undulations. Whenever the irritation is quite local, the result- 

 ing flexure is abrupt, but the curve becomes longer in propor- 

 tion as the irritating body is moved over a greater length, thus 

 showing that the impulses of this character are not readily 

 transmitted. 



During the entire movement of the tendril, distinct torsions 

 are developed, as may readily be seen by following one of the 

 lines of vibrogen tissue. . Oftentimes the torsion is developed 

 to such a degree as to turn the tip fully one-half revolution, 

 thus making it apparently bend upward instead of down- 

 ward. This fact is one which has all the more significance 

 from the statement of Sachs* that in Gucurbitacece " no torsion 

 takes place." Eepeated observations, however, have fully con- 

 firmed its correctness. That this torsion bears an important 

 relation to the circumnutation cannot be doubted, and what its 

 connection is, will be seen later. 



When in its circumnutating, the tendril arm comes in con- 

 tact with an object, it immediately twines about it and grasps 

 it firmly, the basal portion at length forming a double, reversed 

 spiral, which draws more and more closely, and thus secures 

 the plant more firmly to its support. It then rapidly becomes 

 more and more hard and woody. Frequently the tendrils coil 

 about themselves or other tendrils, or catching upon the edge of 

 a leaf, they bend it under into close rolls, which increase in size 

 as the coiling of the tendril progresses. Failing to secure an 

 object of supportj the tendril at length coils up in an irregular, 

 knotted spiral, drops downward and either decays or gradually 

 dries up and becomes hard and woody. 



The woody character, which the tendrils assume in the end, 

 is by no means to be regarded as the result of contact or other 

 mechanical influence, but it is a natural change which neces- 

 sarily follows from the structural elements of the tendril, as 

 will be seen later ; therefore, this serves to supplement, and give 

 additional force to, other changes relating more especially to 

 the former. 



The figure described by the nutating tip is approximately 

 ellipsoidal, the major axis being horizontal, (fig. 2). This axis 

 not infrequently reaches a length of 24 to 2Y cm ; that of the 

 minor axis being from 13 to 22 cm . In Echinocystis lobata, 

 the diameter of the figure, according to Darwin, is even larger 

 than this, measuring from 38 to 41 cm .f While the tendril 

 * Text Book, p. 866. f Climbing Plants, pp. 128-129. 



