*
At the base of the enlarged hypocotyl of Abronia umbellata, where it blends
into the radicle, there is a projection or heel which varies in shape, but
its outline is too angular in our former figure (Fig. 61). The radicle
first protrudes from a small hole at one end of the tough, leathery, winged
fruit. At this period the upper part of the radicle is packed within the
fruit parallel to the hypocotyl, and the single cotyledon is doubled back
parallel to the latter. The swelling of these three parts, and especially
the rapid development of the thick heel between the hypocotyl and radicle
at the point where they are doubled, ruptures the tough fruit at the upper
end and allows the arched hypocotyl to emerge; and this seems to be the
function of the heel. A seed was cut out of the fruit and
* Our attention was called to this case by a brief statement by Nobbe in
his 'Handbuch der Samenkunde,' 1876, p. 215, where a figure is also given
of a seedling of Martynia with a heel or ridge at the junction of the
radicle and hypocotyl. This seed possesses a very hard and tough coat, and
would be likely to require aid in bursting and freeing the cotyledons.
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