Curvature of Tendrils . 
387 
Strains exerted in Curvature and Free Coiling. 
Still farther insight into the amount and character of the 
forces concerned in the rapid formation of a curvature in 
response to contact, and the formation of free coils, is offered 
by the data obtained from a careful measurement of the 
strains set up during such processes. To this end tendrils 
of Cucurbita and Passiflora were placed in horizontal and 
upright positions with the base firmly fixed to a support, 
and extended as far as possible, and the tip attached to 
a Vochting’s dynamometer (X) in such manner that the strain 
set up by any curvature in the organ would be directly 
indicated on the sliding scale carried by one of the compass 
arms of the instrument. In such experiments attention 
was also given to the relative effect of the turgidity of the 
plant upon the strain exerted by the free coils, the time 
necessary for the formation of the coils, and the effect of 
irritation upon the coiling portions. A large number of such 
tests were made, of which those detailed below are fairly 
illustrative. 
1 . 
Sept. 25. After fastening the stem of a Gourd firmly to an iron 
post at the base of a tendril 35 cm. long, the tip was placed loosely in 
the attachment hook of the dynamometer, so that the body of the 
tendril was loosely held between the stem and the dynamometer. 
After it had formed a strong curve at the point of attachment with 
the dynamometer, the latter was fastened firmly in a horizontal 
position, with the tendril vertically extended, and exerting a strain 
of less than 1 gram. 
Sept. 27, 8 a.m. A series of wide coils were forming, inducing 
a strain of 2-5 grams ; at 6 p.m. 8-5 grams. The radius of the coils 
had increased from *5 cm. to 2 cm. 
Sept. 27, 8 a.m. The strain amounted to 12-5 grams. The sun 
shone directly upon the tendril (and upon the terminal portion of the 
plant, 2 M. in length, all day) during the forenoon. 
Sept. 27, 10 a.m. The strain had decreased to n grams, and with 
the shading of the tendril it immediately began to increase. 
