Ancient Plants: Being a Simple Account of the past Vegetation of the Earth and of the Recent Important Discoveries Made in This Realm of NatureStopes, Marie Carmichael
Science
Ancient Plants: Being a Simple Account of the past Vegetation of the Earth and of the Recent Important Discoveries Made in This Realm of Nature
Stopes, Marie Carmichael
Paleobotany
In _Bennettites_ the cones were composed of series of sheathing scales
surrounding a short conical axis on which stood thin radiating stalks,
each bearing a seed. Between them were long-stalked sterile scales with
expanded ends. A part of a cone is illustrated diagrammatically in fig.
71. The whole had much the appearance of a complex fruit. In some
specimens these features alone are present in the cones, but in younger
cones from the American plants further structures are found attached.
Below the main axis of the seed-bearing part of the cone was a series of
large complex leaflike structures closely resembling fern leaves in their
much-divided nature. On the pinnæ of these leaves were crowded
innumerable large sporangia, similar to those of a fern, which provided
the pollen grains. The fossils are particularly well preserved, and have
been found with these male (pollen-bearing) organs in the young unopened
stages, and also in the mature unfolded condition, as well as the
ripening seed cones from which they have faded, just as the stamens fade
from a flower when the seeds enlarge.
[Illustration: Fig. 72.—Diagram of Complete Cone of _Bennettites_
A, Central axis of conical shape terminating in the seed-bearing cone
S. (After Wieland), and bearing successively Br., bracts, comparable
with floral leaves; M, large complex leaves with pollen sacs.]
It appears that these huge complex leaflike structures were really
stamens, but nevertheless they were rolled up in the circinate form as
are young fern leaves, and as they unrolled and spread out round the
central cone they must have had the appearance of a whorl of leaves (see
fig. 72).
This, in a few words, is the main general character of the
fructification. The most important features, on which stress is laid, are
the following. The association of the male and female structures on the
same axis, with the female part _above_ the male. This arrangement is
found only in the flowering plants; the lower plants, which have male and
female on the same cone, have them mixed, or the female below, and are in
any case much simpler in their entire organization. The conical form of
the axis is also important, as is the fact that it terminates in the
seed-bearing structures.
[Illustration: Fig. 73.—Diagram of Cross Section of _Bennettites_,
Seed, with Embryo
_c_, Double-layered seed coat; _n_, crushed nucellus; _cot._, two
cotyledons which practically fill the seed.]
The position of the individual seeds, each on the end of a single stalk,
is remarkable, as are the long-stalked bracts whose shield-like ends join
in the protection of the seeds. These structures together give the cone
much of the appearance of a complex fruit of a flowering plant, but the
structure of the seeds themselves is that of a simple Gymnosperm.
Public-domain text, read in full here on John Shaqi.
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