456 -‘ BOTANICAL GAZETTE [JUNE 
Worcitzky (26) is the only investigator who tested the break- 
ing strength of tendrils with and without a support. He noted 
that a Passiflora tendril which had grasped a support broke at 
600 grams, while one free from a support broke at 350 grams. 
A tendril of Cucurbita Pepo likewise seemed to show greater strength 
of tissues when a support had been grasped. Even supposing 
that these tendrils tested were of the same age (which is not stated 
by the,author), these data have little value in the present paper, 
since it is not known whether the tendrils with a support were 
under tension or contact alone. Worcirzxky found in his anatomi- 
cal study that marked anatomical differences come in with the 
grasping of a support. As to the cause of these anatomical differ- 
ences, none of these investigators have written. VON DERSCHAU 
(24) by an ingenious method sought to separate the influence of 
tension from that of contact in his experiments with petiole 
twiners, by attaching a clamp to the leaf and suspending a weight 
thereon. Contact alone was secured by allowing a petiole merely 
to twine around a stick. It was found that contact alone or 
tension alone, gradually increased, called forth a greater develop- 
ment of mechanical tissue, a still greater increase taking place with 
the combination of both factors. It seems doubtful, however, 
whether the contact stimulus was avoided by this method of 
experimentation. 
Methods _ 
Experiments were conducted in the greenhouse under very 
constant and favorable conditions for growth. 
Special care was taken to secure proper controls, since among 
tendrils, as throughout the plant kingdom, much variation occurs 
in size and vigor of individuals; however, it was found upon 
investigation that tendrils on the same vigorous vine within two 
or three internodes do not vary to an appreciable amount; this 
conclusion was based upon a comparison, by means of camera 
drawings, of sections of the ring of mechanical tissue of several 
tendrils on the same vine and on different vines, all under the 
same conditions (a weight of 15 grams) and all of the same size 
and vigor. These drawings show the areas of mechanical tissue 
of tendrils near each other on the same vine to coincide practically, 
