220 The Palaeontological Record. IT. Plants 
sprang into being in obedience to a Law of Advance (“Vervollkom- 
mungsprincip”), from which other contemporary Lycopods were ex- 
empt, involves us in unnecessary mysticism. On 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 én statu nascendi—in all known 
cases they were already highly developed organs and far removed 
from the crytogamic 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 (p. 208), 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. 
As evolution went on, one function was superadded on another, and 
it appears impossible to resist the conclusion that the whole differen- 
tiation of the seed was a process of adaptation, and consequently 
