Fig. 58. Acanthus mollis: seedling with the hypogean cotyledon on the near
side removed and the radicles cut off; a, blade of first leaf beginning to
expand, with petiole still partially arched; b, second and opposite leaf,
as yet very imperfectly developed; c, hypogean cotyledon on the opposite
side.
In the genus Acanthus the cotyledons are likewise hypogean. In A. mollis, a
single leaf first breaks through the ground with its petiole arched, and
with the opposite leaf much less developed, short, straight, of a yellowish
colour, and with the petiole at first not half as thick as that of the
other. The undeveloped leaf is protected by standing beneath its arched
fellow; and it is an instruc-
[page 79]
tive fact that it is not arched, as it has not to force for itself a
passage through the ground. In the accompanying sketch (Fig. 58) the
petiole of the first leaf has already partially straightened itself, and
the blade is beginning to unfold. The small second leaf ultimately grows to
an equal size with the first, but this process is effected at very
different rates in different individuals: in one instance the second leaf
did not appear fully above the ground until six weeks after the first leaf.
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