or when the plant is unhealthy, the extremity does occasionally
become spiral. I have seen this in a remarkable manner with the ends
of the shoots of the Stauntonia and of the allied Akebia, which
became wound up into a close spire, just like a tendril; and this was
apt to occur after some small, ill-formed leaves had perished. The
explanation, I believe, is, that in such cases the lower parts of the
terminal internodes very gradually and successively 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.

When a revolving shoot strikes a stick, it winds round it rather more
slowly than it revolves. For instance, a shoot of the Ceropegia,
revolved in 6 hrs., but took 9 hrs. 30 m. to make one complete spire
round a stick; Aristolochia gigas revolved in about 5 hrs., but took
9 hrs. 15 m. to complete its spire. This, I presume, is due to the
continued disturbance of the impelling force by the arrestment of the
movement at successive points; and we shall hereafter see that even
shaking a plant retards the revolving movement. The terminal
internodes of a long, much-inclined, revolving shoot of the
Ceropegia, after they had wound round a stick, always slipped up it,
so as to render the spire more open than it was at first; and this
was probably in part due to the force which caused the revolutions,
being now almost freed from the constraint of gravity and allowed to
act freely. With the Wistaria, on the other hand, a long horizontal
shoot wound itself at first into a very close spire, which remained
unchanged; but subsequently, as the shoot twined spirally up its
support, it made a much more open spire. With all the many plants
which were allowed freely to ascend a support, the terminal
internodes made at first a close spire; and this, during windy
weather, served to keep the shoots in close contact with their