In the course of a few hours the
hook was thus converted into a loop with the apex of the shoot pointing
straight downwards. The longer axis of the loop was at first horizontal,
but afterwards became vertical. During this same time the basal part of the
hook (and subsequently of the loop) curved itself slowly upwards; and this
must have been wholly due to apogeotropism in opposition to hyponasty. The
loop was then fastened upside down, so that its basal half would be
simultaneously acted on by hyponasty (if present) and by apogeotropism; and
now it curved itself so greatly upwards in the course of only 4 h. that
there could hardly be a doubt that both forces were acting
[page 274]
together. At the same time the loop became open and was thus reconverted
into a hook, and this apparently was effected by the geotropic movement of
the apex in opposition to epinasty. In the case of Ampelopsis hederacea,
weight plays, as far as we could judge, a more important part in the
hooking of the tip.
In order to ascertain whether the shoots of A. tricuspidata in
straightening themselves under the combined action of hyponasty and
apogeotropism moved in a simple straight course, or whether they
circumnutated, glass filaments were fixed to the crowns of four hooked tips
standing in their natural position; and the movements of the filaments were
traced on a vertical glass.
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