56 
POPULAR SCIENCE REVIEW. 
became twisted three times round its own axis, while the 
internode itself gave no less than 37 revolutions before be- 
coming rigid. It is a curious point in connection with this 
twisting that it is in a direct relation to the inequalities of, or 
freedom from the support ; for stems do not become twisted 
if allowed to climb small glass rods, but only rough sticks or 
when hanging freely in the air. “ The most probable view,” 
Mr. Darwin says, “ is that the stem twists itself to gain 
rigidity (on the same principle that a much twisted rope is 
stiffer than a slackly twisted one), so as to be enabled either 
to pass over inequalities in its spiral ascent, or to carry its 
own weight when allowed to revolve freely.” 
He offers the following in explanation : — f f that the lower 
parts of the terminal internodes very gradually and success 
sively lose their power of movement, whilst the portions just 
above move onwards, and in their turn become motionless, 
and this ends in forming an irregular spire.” 
The following is our author's explanation of the purport of 
this motion : — 
“ The purpose of this spontaneous revolving motion, or, more strictly 
speaking, of the continuous bending movement successively to all points 
of the compass, is obviously in part to favour the shoot finding a support ; 
. , . but when this is gained, the motion at the point of contact is 
^arrested ; while the free part projecting above continues to revolve, and by 
.the very motion cannot fail to twine itself round the support.” 
Mr. Darwin gives an interesting series of tables showing 
the direction and rate of motion of several twining plants 
.selected from all parts of the vegetable kingdom, proving 
that every kind behaves irL a nearly uniform manner. We 
purpose giving some of the more important conclusions 
deduced. 
Of thirty-nine plants, twenty-five revolved in a course 
opposed to, and twelve with, the sun ; two revolved both with 
and against the sun. No instance is at present known of 
two species of the same genus twining in opposite directions. 
The average rate at which the first circle of revolution is 
described is about 6h. 10m., computed from thirty-five different 
plants ; the longest period being 26h. 15m., viz., of a young 
shoot of Lapagerea rosea ( Philesiacece ) ; while the most rapid 
was that of Scyjphanthus elegans (. Loasacece ), viz. Ih. 17m. 
The average rate of twining plants is 5h. 45m. for five revo- 
lutions. It must be borne in mind that young shoots 
commence slowly, and do not arrive at the maximum time of 
rotation until they have accomplished several circles or ellipses 
as the case may be. 
