Curvature of Tendrils. 383 
and he calls especial attention to the fact that the elongation 
of the longitudinal membranes is in no sense growth, since 
their dry weight does not increase. The only recent work 
dealing with the mechanism of the tendril alone is that of 
Penhallow (XVII, p. 75), in which he concludes that ‘move- 
ments due to irritation depend upon the continued elongation 
of the opposite side, together with cessation of growth and 
contraction in the irritated parts.’ In support of this con- 
clusion, however, no additional facts, except the accentuated 
development of the collenchymatous tissue of the concave 
side, are given. 
While, as noted above, it has been proved that the convex 
side of curving organs does not show a preponderance of 
osmotic substance, in opposition to the conclusions of DeVries, 
it is evident that such conditions would be of value only 
in conjunction with certain mechanical features. Moreover, 
I have been unable to verify the immediate facts of De Vries’ 
plasmolytic researches on tendrils of S icy os angidatus , Cu- 
curbita Pepo , Bryonia dioica , Echinocystis lobata , and Passiflora 
gracilis. He found that the plasmolysis of freshly induced 
curvatures of stems and tendrils resulted finally in the 
lengthening of the radius of curvature, perhaps to such extent 
that the organ became straightened. At first, however, a 
minor amount of shortening of the radius occurred. That 
such may be the case with geotropically or heliotropically 
induced curvatures of stems and petioles under certain con- 
ditions is confirmed ; but is by no means invariable, as has 
been shown by Wiesner (XXI). O. Muller (XIV) found that 
the plasmolysis of tendrils, stimulated or unstimulated, might 
be followed either by increased or decreased curvature, in 
accordance with certain unexplained inward differences. 
My own results are completely at variance with those of 
De Vries, and differ from those of Muller in that with 
weak solutions plasmolysis invariably resulted finally in the 
shortening of the radius of curvature, in both stimulated and 
unstimulated organs, and this decrease continued with minor 
variations so long as they were alive. The following data, 
