cence of the
two nuclei within the substance of the germinal vesicle causes the
latter to secrete a wall, and to form a new plant by division, being
nourished the while by the mother plant, from whose tissues the young
embryo plant contained in the seed only becomes free when it is in an
advanced stage of differentiation.

Perhaps the most remarkable cases of fertilization occur in the Florideae
or red seaweeds, to which class the well-known Irish moss belongs.

Here, instead of the cell which is fertilized by the rounded
spermatozoid producing a new plant through the medium of spores, some
other cell which is quite distinct from the primarily fertilized cell
carries on the reproductive process.

If the allied group of the Coleochaeteae is considered together with the
Florideae, we find a transition between the ordinary case of Coleochaete
and that of Dudresnaya. In Coleochaete, the male cell is a round
spermatozoid, and the female cell an oosphere contained in the base of a
cell which is elongated into an open and hair-like tube called the
trichogyne. The spermatozoid coalesces with the oosphere, which secretes
a wall, becomes surrounded with a covering of cells called a cystocarp,
which springs from cells below the trichogyne, and after the whole
structure falls from the parent plant, spores are developed from the
oospore, and from them arises a new generation.

In Dudresnaya, on the other hand, the spermatozoid coalesces indeed with
the trichogyne, but this does not develop further. From below the
trichogyne, however, spring several branches, which run to the ends of
adjacent branches, with the apical cells of which they conjugate, and
the result of this conjugation is the development of a cystocarp similar
to that of Coleochaete. The remarkable point here is the way in which the
effect of the fertilizing process is carried from one cell to another
entirely distinct from it.

Thus I have endeavored to sum up the processes of asexual and of sexual
reproduction. But it is a peculiar characteristic of most classes of
plants that the cycle of their existence is not complete until both
methods of reproduction have been called into play, and that the
structure produced by one method is entirely different from that
produced by the other method.

Indeed, it is only in some algae and fungi that the reproductive cells of
one generation produce a generation similar to the parent; in all other
plants a generation A produc