8 gS ees a 
14 TWINING PLANTS. Cuar. L. 
other internodes; for a line painted on the convex 
surface first becomes lateral and then concave; but, 
owing to the youth of these terminal internodes, the. 
reversal of the hook is a slower process than that of the 
revolving movement.* This strongly marked tendency , 
in the young, terminal and flexible internodes, to bend 
in a greater degree or more abruptly than the other 
internodes, is of service to the plant ; for not only does 
the hook thus formed sometimes serve to catch a 
support, but (and this seems to be much more impor- 
tant) it causes the extremity of the shoot to embrace 
the support much more closely than it could otherwise 
have done, and thus aids in preventing the stem from 
being blown away during windy weather, as I have 
many times observed. In Lonicera brachypoda the 
hook only straightens itself periodically, and never 
becomes reversed. I will not assert that the tips of 
all twining plants when hooked, either reverse them- 
selves or become periodically straight, in the manner 
just described ; for the hooked form may in some cases 
be permanent, and be due to the manner of growth of 
the species, as with the tips of the shoots of the com- 
mon vine, and more plainly with those of Cissus dis- 
color—plants which are not spiral twiners. 
The first purpose of the spontaneous revolving 
movement, or, more strictly speaking, of the con- 
* The mechanism by which the H. de Vries (ibid. p. 837): he 
end of the shoot remains hooked concludes that “it depends on the 
appears to be a difficult and relation between the rapidity of tor- 
complex problem, discussed by Dr. sion and the rapidity of nutation”” 
