ge themselves only after contact
of the cell with one of another filament of the plant. This zygoblast
only becomes free after the process of conjugation, as described below.

3. The oosphere of characeae, mosses and liverworts, and vascular
cryptogams, where in special structures produced by cell-divisions there
arise single primordial cells, which divide into two portions, of which
the upper portion dissolves or becomes mucilaginous, while the lower
contracts and rearranges itself to form the oosphere.

4. Spores of mosses and liverworts, of vascular cryptogams, and pollen
cells of phanerogams, which are the analogue of the spores.

The type in all these cases is this: A mother-cell produces by
cell-division four daughter-cells. This is so far vegetative. Each
daughter-cell contracts and becomes more or less rounded, secretes a
wall of its own, and by the bursting or absorption of the wall of its
mother-cell becomes free. This is evidently a rejuvenescence.

Examples of reproductive cells formed by free-cell formation are:

1. The ascospores of fungi and algae.

2. The zoospores or mobile spores of many algae and fungi.

3. The germinal vesicles of phanerogams.

The next portion of my subject is the study of the methods by which
these special cells reproduce the plant.

1st. Asexual methods.

1. Rejuvenescence gives rise to a swarm-spore or zoospore. The whole of
the protoplasm of a cell contracts, becomes rounded and rearranged, and
escapes into the water, in which the plant floats as a mass of
protoplasm, clear at one end and provided with cilia by which it is
enabled to move, until after a time it comes to rest, and after
secreting a wall forms a new plant by ordinary cell-division. Example:
Oedogonium.

2. Free-cell formation forms swarm-spores which behave as above.
Example: Achlya.

3. Free-cell formation forms the typical motionless spore of algae and
fungi. For instance, in the asci of lichens there are formed from a
portion of the protoplasm four or more small ascospores, which secrete a
cell-wall and lie loose in the ascus. Occasionally these spores may
consist of two or more cells. They are set free by the rupture of the
ascus, and germinate by putting out through their walls one or more
filaments which branch and form the thallus of a new individual. Various
other spores formed in the same way are known as _tetraspores_, etc.

4. Cell-division with rejuvenescence forms the spores of mosses a