Tropaeolum minus (?) (var. Tom Thumb) (Tropaeoleae).--The cotyledons are
hypogean, or never rise above the ground. By removing the soil a buried
epicotyl or plumule was found, with its summit arched abruptly downwards,
like the arched hypocotyl of the cabbage previously described. A glass
filament with a bead at its end was affixed to the basal half or leg, just
above the hypogean cotyledons, which were again almost surrounded by loose
earth. The tracing (Fig. 16) shows the course of the bead during 11 h.
After the last dot given in the figure, the bead moved to a great distance,
and finally off the glass, in the direction indicated by the broken line.
This great movement, due to increased growth along the concave surface of
the arch, was caused by the basal leg bending backwards from the upper
part, that is in a direction opposite to the dependent tip, in the same
manner as occurred with the hypocotyl of the cabbage. Another buried and
arched epicotyl was observed in the same manner, excepting that the two
legs of the arch were tied together with fine silk for the sake of
preventing the great movement just mentioned.
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