As ferns differ so much in structure from phanerogamic plants, it may
be worth while here to show that twining ferns do not differ in their
habits from other twining plants. In Lygodium articulatum the two
internodes of the stem (properly the rachis) which are first formed
above the root-stock do not move; the third from the ground revolves,
but at first very slowly. This species is a slow revolver: but L.
scandens made five revolutions, each at the average rate of 5 hrs. 45
m.; and this represents fairly well the usual rate, taking quick and
slow movers, amongst phanerogamic plants. The rate was accelerated
by increased temperature. At each stage of growth only the two upper
internodes revolved. A line painted along the convex surface of a
revolving internode becomes first lateral, then concave, then lateral
and ultimately again convex. Neither the internodes nor the petioles
are irritable when rubbed. The movement is in the usual direction,
namely, in opposition to the course of the sun; and when the stem
twines round a thin stick, it becomes twisted on its own axis in the
same direction. After the young internodes have twined round a
stick, their continued growth causes them to slip a little upwards.
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