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 the second or asexual generation.  The peculiarity of this asexual or spore-bearing plant is that it is parasitic on the sexual plant; the two generations, although not organically connected, yet remain in close contact, and the spore-bearing generation is at all events for a time nourished by the leafy sexual generation.

The spore-bearing generation consists of a long stalk, closely held below by the cells of the base of the archegonium; this supports a broadened portion which contains the spores, and the top is covered with the remains of the neck of the archegonium forming the calyptra.

The spores arise from special or mother-cells by a process of division, or it may be even termed free-cell formation, the protoplasm of each mother-cell dividing into four parts, each of which contracts, secretes a wall, and thus by rejuvenescence becomes a spore, and by the absorption of the mother-cells the spores lie loose in the spore sac.  The spores are set free by the bursting of their chamber, and each germinates, putting out a branched thread of cells called a protonema, which may perhaps properly be termed a third generation in the cycle of the plant; for it is only from buds developed on this protonema that the leafy sexual plant arises.

The characteristics, then, of the mosses are, that the sexual generation is leafy, the one or two asexual generations are thalloid, and that the spore-bearing generation is in parasitic connection with the sexual generation.

In the case of the fern, these conditions are very different.

The sexual generation is a small green thalloid structure called a prothallium, which bears antheridia and archegonia, each archegonium having a neck-canal and oosphere, which is fertilized just as in the moss.