The life cycle of moss
As with any plant without seeds, "where do mosses come from?" is a logical question. The old riddle of which comes first, the chicken or the egg, can be applied to moss as well ... for there is an egg, and there is a sperm. But there is also protonema, and this seems the best place to start in any consideration of moss origins.
Protonema is a fine green filamentous web beginning with the division of a single cell and spreading out over a favourable growing medium, such as soil, wood or rock. The web sends down tiny rhizoids for nutrition and support, and in due time produces little buds on the surface that grow into moss plants. These may be male or female plants, or they may be sterile.
Where does the protonema itself come from? Well, it starts growing when a single spore from a ripened moss capsule finds itself surrounded by all the right conditions, swells and breaks open, and releases its treasures of life and growth. But protonema will also develop asexually from the living cells of chopped pieces of any part of the plant. In other words, you can cut up a moss plant and get any part to grow into separate plants! Indeed, some mosses depend on being disturbed and broken up in dry weather for distribution and revival in new locations. It is believed that by far the greatest proportion of moss propagation is by asexual reproduction.
Now let's turn to the sporophytes, those little spikey projections above many beds of moss that can be produced only by the union of male and female, sperm and egg. Each sporophyte stalk bears its capsule-shaped spore case at the top, which is the offspring of sexual union hosted by the female, or mother plant.
I find it very significant that the private life of mosses bears, at least to me, no small resemblance to our own. In the mosses, for instance, the male and female parts of some species may be found "intermingling in the same receptacle" (in the same bed). In other species the male and female may be found in separate locations (beds) on the same stem (room). Or they may occupy separate rooms (stems) in the same house (plant). As long as the male and female parts occur on the same plant, the moss is said to be monoecious. But if they can be found only on different plants (houses), the species is dioecious. It is often necessary to know whether a moss is monoecious or dioecious for positive identification. In a larger context, mosses are classed together with most other seedless plants, as Cryptogamia (spore-bearing plants) and the word means, literally, "hidden marriage"!
The domestic life of moss differs from ours in at least one way, however. In human society, the male usually takes the female into shared occupancy of
his home, or their home. In moss society, the male is often an occupant of the female's "house" in one way or another, maybe even an insignificant appendage to her. It is true there are species where the male is an independent, even colourful dandy in his own "house" which is sometimes part of a separate all-male "apartment" or "subdivision." The antheridium, or male sexual part, of Juniper Moss is an example with its open, red-lined cupshape, in company with its kind, blazing like red stars in the dewy grass; here we have a fine case of the dominant male. But usually it is the female who plays the dominant role. She is superior in physical size and station. In the role of "mother," she visibly supports the sporophytes, the fruit of their sexual union.
Now, let's see how all this happens. Put as simply as possible, the female plant produces her egg in a flask-like organ called the archegonium. And the male plant produces sperm in the antheridium, which is situated in his saucer-shaped perigonium.
Although land-bound as a species for millions of years, mosses still require water as a medium for reproduction. So the egg and sperm are both matured and released at a time when the plants are bathed in moisture from rain or dew. Some mysterious attraction brings the sperm cell swimming with its flagellate appendages through the film of moisture on the surface of the plant to the nearest mature egg. This maturity is indicated by a gluey substance exuding from the mouth of the female archegonium.
But what is this mysterious force that draws the male cell unerringly to the oozing archegonium into which it dives to unite with the egg? We can feel the attraction of electrical energy in two magnets, but how do you comprehend the chemical attraction between two bodies joined only by moisture over an uncertain and hazardous distance? Perhaps there's no easy answer to this obvious question. E.V. Watson in his
The Structure and Life of Bryophytes drops a casual bit of information that has intrigued me: the gluey substance exuded by the archegonium is
pure cane sugar! So what else is new? The mosses did it first. To ensure perpetuation of their kind, the female is provided with accessory sweets for enticement of the male!