After hypocotyls or epicotyls have
emerged from the ground, they quickly become perfectly straight. No trace
is left of their former abrupt curvature, excepting in the case of Allium
cepa, in which the cotyledon rarely becomes quite straight, owing to the
protuberance developed on the crown of the arch.
The increased growth along the inner surface of the arch which renders it
straight, apparently begins in the basal leg or that which is united to the
radicle; for this leg, as we often observed, is first bowed backwards from
the other leg. This movement facilitates the withdrawal of the tip of the
epicotyl or of the cotyledons, as the case may be, from within the
seed-coats and from the ground. But the cotyledons often emerge from the
ground still tightly enclosed within the seed-coats, which apparently serve
to protect them. The seed-coats are afterwards ruptured and cast off by the
swelling of the closely conjoined cotyledons, and not by any movement or
their separation from one another.
Nevertheless, in some few cases, especially with the
[page 102]
Cucurbitaceae, the seed-coats are ruptured by a curious contrivance,
described by M.
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