Curvature of Tendrils . 381 
encircling a support and of a free portion are wholly without 
significance, since he has failed to indicate the positions of 
the zones measured with regard to the region of maximum 
growth, which in the earlier stages lies in the basal portion of 
the tendril and progresses forzvard in an oscillating manner 
until it may occupy a position distal to the middle of the tendril 
but from which it finally recedes . 
From the numerous measurements of the elongation of the 
convex surface of portions of tendrils encircling a support, 
the writer has never found an increase greater than 50 per 
cent, of the maximum given above, and De Vries’ theory, that 
curvature around a support is due to the accelerated growth 
of the convex side, is no longer tenable. Furthermore, if the 
contact-curvature of the tendril were due to growth, it might 
be expected that the organ would be more highly irritable in 
the region of greatest growth, but the zone of greatest growth 
never at any time coincides voith the zone of greatest irritability , 
which lies near the tip. 
That a difference does exist between the features of 
growth of a portion of a free tendril and one which has 
encircled a support, is quite apparent. Such differences 
consist in a slightly lessened elongation of the convex side 
and a greatly decreased elongation of the concave side, 
which are to be considered as consequences, not causes of 
contact curvature. It is to be readily seen that when a 
tendril is coiled around a support by any force, whether 
internal or external, the pressure exerted upon the concave 
side from the support and the internal strains would 
exert a very marked effect on the growth of the tissue so 
affected. The alterations in the growth of a curved tendril, 
as described by Worgitzky (XXII), are exactly such as 
might follow from the altered mechanical conditions. These 
changes consist principally in the tangential division of the 
epidermal cells, followed by a thickening of their walls which 
extends in a marked degree to the collenchyma and cortical 
parenchyma, accompanied by a strong development of pro- 
senchymatous tissue. In the mean time the growth of the 
