224 
increases slightly and, when placed in water, the tendril 
straightens markedly though a large part of the original cur- 
vature remains, having been made permanent either by growth 
or by a change in the elasticity or extensibility of the cell 
walls of the sides affected. The tendrils are irritable to contact 
with one another, especially if the terminal part of one touches 
the basal part of another, or if one tendril is attached, in 
which cases the coiling may become permanent. 
In all the plants hitherto mentioned, the hooks, hook-tendrils 
or tendrils respond to contact with others of the same plant 
in a manner commensurate to the pressure, and to the area 
and roughness of the surfaces in contact. Darwin !) states that 
the tendrils of Lchinocystis lobata and Passifora gracilis are not 
irritable to contact with tendrils of the same plant and may 
touch one another without any coiling or curvature being pro- 
duced. He ascribes this to the tendrils being accustomed to, 
and uo longer responding to, this kind of contact. In certain 
cases, however, (Bryonia etc.) he mentions that tendrils may 
be found, which have coiled around one another, they possessing. 
apparently no special discriminatory power. Przrrer *) has shewn 
that the tendrils of Steyos angulatus, Bryonia dioica and Passifiora 
gracilis are sensitive to contact with tendrils of the same plant, 
provided the sensitive side is the one touched. Owing to the 
smoothness of the epidermal surface of the tendrils and their 
lightness and thinness, the stimulus is a nearly minimal one 
and the tendril may become accustomed to it and straighten 
again, as is indeed always the case when a minimal stimulus is 
employed. Even if this does not take place, and the stimulus 
is sufficient to produce a considerable curvature, still, owing 
to the smoothness and pliability of the tendrils, as nutation 
continues, the tendrils separate, move over one another, and 
then soon straighten. Tendrils, which are thin and have 4 
very smooth epidermis, are the ones which are least sensitive 
1) Darwin. Climbing Plants 1875. 
2) Zar Kenntniss der Kontacktreize, Untersuch. aus. dem. Bot. Inst. 2u Tiibinge? 
p. 495. Bd. J. Hft. IV. 1885, 
