10 TWINING PLANTS. Cuap. I. 
generally and strongly with twining-plants than with 
other plants, that there must be some connexion 
between the capacity for twining and axial twisting. 
The stem probably gains rigidity by being twisted 
(on the same principle that a much twisted rope is 
stiffer than a slackly twisted one), and is thus in- 
directly benefited so as to be enabled to pass over 
inequalities in its spiral ascent, and to carry its own 
weight when allowed to revolve freely.* 
I have alluded to the twisting which necessarily 
follows on mechanical principles from the spiral 
ascent of a stem, namely, one twist for each spire 
completed. This was well shown by painting straight 
lines on living stems, and then allowing them to twine ; 
but, as I shall have to recur to this subject under 
Tendrils, it may be here passed over. 
The revolving movement of a twining plant has 
been compared with that of the tip of a sapling, moved 
round and round by the hand held some way down 
the stem; but there is one important difference. 
The upper part of the sapling when thus moved 
five were observed to be twisted 
in an opposite direction. The 
Spanish chestnut is often much 
twisted: there is an interesting 
article on this subject in the 
‘Scottish Farmer, 1865, p. 833. 
* It is well known that the 
stems of many plants occasionally 
become spirally twisted in a 
monstrous manner; and after my 
paper was read before the Linnean 
Society. Dr. Maxwell Masters re- 
marked to me in a letter that 
“some of these cases, if not all, 
are dependent upon some obstacle 
or resistance to their upward 
growth.” This conclusion agrees 
with what I have said about the 
twisting of stems, which have 
twined round rugged supports; 
but does not preclude the twist- 
ing being of service to the plant 
by giving greater rigidity to the 
stem, 
