Others believe that the ovuliferous scale is composed of two leaves
situated laterally and consolidated representing a shoot in the axis of
the bract. There is some support for this in the fact that in certain
abnormal cones which show proliferation a short axis appears in the
axil of the bract and bears lateral leaves, and in some cases all
gradations are present between these lateral leaves on the axis and
their consolidation into an ovuliferous scale. In the normal condition
of the ovuliferous scale the axis has disappeared and the shoot is
represented only by the consolidated leaves, which would represent then
the macrosporophylls (or carpels) each bearing one macrosporangium
(ovule).
[Illustration: Fig. 362.
Pine seed, section of, _sc_, seed coat; _n_, remains of nucellus;
_end_, endosperm (= female gametophyte); _emb_, embryo = young
sporophyte. Seed coat and nucellus = remains of old sporophyte.]
[Illustration: Fig. 363. Embryo of white pine removed from seed, showing
several cotyledons.]
[Illustration: Fig. 364. Pine seedling just emerging from the ground.]
One of the most interesting and plausible views is that of Celakovsky.
He believes that the axial shoot is reduced to two ovules, that the
ovules have two integuments, but the outer integument of each has
become proliferated into scales which are consolidated. In this
proliferation of the outer integument it is thrown off from the ovule
so that it only remains attached to one side and the larger part of the
ovule is thus left with only one integument. This view is supported
by the fact that in gingko, for example (another gymnosperm), the
outer integument (the “collar”) sometimes proliferates into a leaf.
Celakovsky’s view is, therefore, not very different from the second one
mentioned above.
[Illustration: Fig. 365. White pine seedling casting seed coats.]
CHAPTER XXXIV.
FURTHER STUDIES ON GYMNOSPERMS.
Cycas.
[Illustration: Fig. 366. Macrosporophyll of Cycas revoluta.]
=627.= In such gymnosperms as cycas, illustrated in the
frontispiece, there is a close resemblance to the members of the fern
group, especially the ferns themselves. This is at once suggested by
the form of the leaves. The stem is short and thick. The leaves have a
stout midrib and numerous narrow pinnæ. In the center of this rosette
of leaves are numerous smaller leaves, closely overlapping like bud
scales. If we remove one of these at the time the fruit is forming we
see that in general it conforms to the plan of the large leaves. There
are a midrib and a number of narrow pinnæ near the free end, the entire
leaf being covered with woolly hairs. But at the lower end, in place of
the pinnæ, we see oval bodies. These are the macrosporangia (ovules)
of cycas, and correspond to the macrosporangia of selaginella, and the
leaf is the macrosporophyll.
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