ermatozoids directly, leaving them to find their own way to the
female cells. It thus appears that there were once Spermophyta without
pollen-tubes. The pollen-tube method ultimately prevailed, becoming a
constant "morphological character," for no other reason than because,
under the new conditions, it provided a more perfect mechanism for the
accomplishment of the act of fertilisation. We have still, in the Cycads
and Ginkgo, the transitional case, where the tube remains short, serves
mainly as an anchor and water-reservoir, but yet is able, by its slight
growth, to give the spermatozoids a "lift" in the right direction. In
other Seed-plants the sperms are mere passengers, carried all the way by
the pollen-tube; this fact has alone rendered the Angiospermous method
of fertilisation through a stigma possible.

We may next take the seed itself--the very type of a morphological
character. Our fossil record does not go far enough back to tell us the
origin of the seed in the Cycadophyta and Pteridosperms (the main line
of its development) but some interesting sidelights may be obtained from
the Lycopod phylum. In two Palaeozoic genera, as we have seen, seed-like
organs are known to have been developed, resembling true seeds in the
presence of an integument and of a single functional embryo-sac, as well
as in some other points. We will call these organs "seeds" for the sake
of shortness. In one genus (Lepidocarpon) the seeds were borne on a cone
indistinguishable from that of the ordinary cryptogamic Lepidodendreae,
the typical Lycopods of the period, while the seed itself retained
much of the detailed structure of the sporangium of that family. In the
second genus, Miadesmia, the seed-bearing plant was herbaceous, and much
like a recent Selaginella. (See Margaret Benson, "Miadesmia membranacea,
a new Palaeozoic Lycopod with a seed-like structure", "Phil. Trans.
Royal Soc. Vol." 199, B. 1908.) The seeds of the two genera are
differently constructed, and evidently had an independent origin. Here,
then, we have seeds arising casually, as it were, at different points
among plants which otherwise retain all the characters of their
cryptogamic fellows; the seed is not yet a morphological character of
importance. To suppose that in these isolated cases the seed sprang into
being in obedience to a Law of Advance ("Vervollkommungsprincip"),
from which other contemporary Lycopods were exempt, involves us in
unnecessary mysticism. On