es are unlike generation B, which may either
go on to produce another generation, C, and then back to A, or it may go
on producing B's until one of these reproduces A, or again it may
directly reproduce; A. Thus we have the three types:

1. A-B-C.--A-B-C.--A..................... etc.
2. A-B-B.--B-B...................B--A ... etc.
3. A B A B A............................. etc.

The first case is not common, the usual number of generations being two
only; but a typical example of the occurrence of three generations is in
such fungi as _Puccinia Graminis_. Here the first generation grows on
barberry leaves, and produces a kind of spore called an _aecidium spore_.
These aecidium spores germinate only on a grass stem or leaf, and a
distinct generation is produced, having a particular kind of spore
called an _uredospore_. The uredospore forms fresh generations of the
same kind until the close of the summer, when the third generation with
another kind of spore, called a _teleutospore_, is produced.

The teleutospores only germinate on barberry leaves, and there reproduce
the original aecidium generation.

Thus we have the series A.B.B.B ... BCA

In this instance all the generations are asexual, but the most common
case is for the sexual and the asexual generations to alternate. I will
describe as examples the reproduction of a moss, a fern, and a
dicotyledon.

In such a typical moss as Funaria, we have the following cycle of
developments: The sexual generation is a dioecious leafy structure,
having a central elongated axis, with leaves arranged regularly around
and along it. At the top of the axis in the male plant rise the
antheridia, surrounded by an envelope of modified leaves called the
perigonium. The antheridia are stalked sacs, with a single wall of
cells, and the spiral antherozoids arise by free-cell formation from the
cells of the interior. They are discharged by the bursting of the
antheridium, together with a mucilage formed of the degraded walls of
their mother cells.

In the female plant there arise at the apex of the stem, surrounded by
an envelope of ordinary leaves, several archegonia. These are of the
ordinary type of those organs, namely, a broad lower portion, containing
a naked oosphere and a long narrow neck with a central canal leading to
the oosphere. Down this canal pass one or more antherozoids, which
become absorbed into the oosphere, and this then secretes a wall, and
from it grows th