the other hand it is not difficult to see how
these seeds may have arisen, as adaptive structures, under the influence
of Natural Selection. The seed-like structure afforded protection to the
prothallus, and may have enabled the embryo to be launched on the world
in greater security. There was further, as we may suppose, a gain in
certainty of fertilisation. As the writer has pointed out elsewhere,
the chances against the necessary association of the small male with the
large female spores must have been enormously great when the cones were
borne high up on tall trees. The same difficulty may have existed in the
case of the herbaceous Miadesmia, if, as Miss Benson conjectures, it was
an epiphyte. One way of solving the problem was for pollination to take
place while the megaspore was still on the parent plant, and this is
just what the formation of an ovule or seed was likely to secure.

The seeds of the Pteridosperms, unlike those of the Lycopod stock,
have not yet been found in statu nascendi--in all known cases they were
already highly developed organs and far removed from the cryptogamic
sporangium. But in two respects we find that these seeds, or some
of them, had not yet realised their possibilities. In the seed
of Lyginodendron and other cases the micropyle, or orifice of the
integument, was not the passage through which the pollen entered; the
open neck of the pollen-chamber protruded through the micropyle and
itself received the pollen. We have met with an analogous case, at a
more advanced stage of evolution, in the Bennettiteae, where the wall
of the gynaecium, though otherwise closed, did not provide a stigma to
catch the pollen, but allowed the micropyles of the ovules to protrude
and receive the pollen in the old gymnospermous fashion. The integument
in the one case and the pistil in the other had not yet assumed all
the functions to which the organ ultimately became adapted. Again, no
Palaeozoic seed has yet been found to contain an embryo, though the
preservation is often good enough for it to have been recognised if
present. It is probable that the nursing of the embryo had not yet come
to be one of the functions of the seed, and that the whole embryonic
development was relegated to the germination stage.

In these two points, the reception of the pollen by the micropyle and
the nursing of the embryo, it appears that many Palaeozoic seeds
were imperfect, as compared with the typical seeds of later times