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There are two divisions or phyla here: the Bryophyta, or mosses, and the Hepaticae, or liverworts. They are often combined into the one phylum, the bryophytes. The essential common feature of mosses and liverworts is that the sporophyte generation is a kind of symbiont with the gametophyte. The latter grows out of the ground in moist places; the former grows out of the gametophyte. The life cycle of a moss is shown in Fig. 12-4. As is characteristic of gametophytes and sporophytes, the one producing the gametes is haploid, the other is diploid. Meiosis occurs in the diploid sporophyte, and haploid spores are formed and then released to germinate and thus start a new gametophyte generation.

In mosses, water is absorbed through rhizoids. These are filamentous chains of cells that extend underground, like roots. The stem is a vertical growth of cells from the rhizoids. Never over a few inches long, it brings water and dissolved minerals up to the small leaflets that grow directly out of the stem. Active photosynthesis occurs in the leaflets. Because the cells are small, water, nutrients, and products of photosynthesis can be distributed by diffusion throughout the plant body. This is thought to be the reason why cells and tissue specialized for a transport function are notably absent. Vascular plants without seeds. Not only do all the remaining land plants show vascular tissues, their sporophyte and gametophyte generations differ from those seen in the mosses and liverworts. From among the various seedless vascular plants, let us look at the ferns as typifying the essential features of this group.

A fern, as most commonly encountered, is a sporophyte, or diploid plant. Its most visible part is the frond (leaf), which extends gracefully upward from a root stock which in most cases has roots extending into the soil. On the underside of the frond, which can be undivided or subdivided into a delicate array of subparts, there are quite often sporangia containing spores. After meiosis, the spores formed here are released; upon germination, a spore produces a tiny, haploid gametophyte. This tiny plantlet develops both sperm-forming and egg-forming parts. A sperm fertilizes an egg and initiates a new diploid sporophyte.

Note, especially, the relative roles of the sporophyte and the gametophyte. Both are necessary for a complete life cycle, but here they draw independently from their environment to exist autonomously. There is no dependence of sporophyte on gametophyte, such as the symbiosis seen in liverworts and mosses. Furthermore, the sporophyte is the more conspicuous of the two plant stages or generations. As regards the details of sporophyte structure, we find the already-mentioned root structures and frond. Vascular tissues are quite well developed in the stem of the frond. Here we can see the xylem, which functions principally to transport water and dissolved minerals, and the phloem, which distributes dissolved foods (mostly carbohydrates)