We believe that the weight of the apex is an unimportant
element, because on horizontal or inclined shoots the hook is often
extended horizontally or even faces upwards. Moreover shoots frequently
form loops instead of hooks; and in this case the
* 'Sitzb. der k. Akad. der Wissensch.,' Vienna, Jan. 1880, p. 16.
[page 273]
Fig. 122. Ampelopsis tricuspidata: hyponastic movement of hooked tip of
leading shoot, traced from 8.10 A.M. July 13th to 8 A.M. 15th. Apex of
shoot 5 ? inches from the vertical glass. Plant illuminated through a
skylight. Temp. 17 1/2o - 19o C. Diagram reduced to one-third of original
scale.
extreme part, instead of hanging vertically down as would follow if weight
was the efficient cause, extends horizontally or even points upwards. A
shoot, which terminated in a rather open hook, was fastened in a highly
inclined downward position, so that the concave side faced upwards, and the
result was that the apex at first curved upwards. This apparently was due
to epinasty and not to apogeotropism, for the apex, soon after passing the
perpendicular, curved so rapidly downwards that we could not doubt that the
movement was at least aided by geotropism.
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