•Charateristics of Bryophytic plants and Pteridophytic plants.
Answers
As we pass from mosses to ferns, we see a gradual transition from primitive to modern traits. There are two major trends you should focus on in today's lab. The first is a transition in life cycles, the second is a change in basic internal structure.
First, all plants undergo an alternation of generations, between a haploid gametophyte stage and a diploid sporophyte stage. In the most primitive plants, like mosses, the gametophyte is dominant (i.e. it's big and green). In higher plants like ferns and fern allies, the sporophyte stage is dominant. Gametophytes produce gametes (sperm and eggs) in a special structure called a gametangium (-ia), while sporophytes produce spores in a special structure called a sporangium (-ia).
Second, all plants need to get water to their cells. Primitive bryophytes like mosses and liverworts are so small that they can rely on diffusion to move water in and out of the plant. Mosses have a few strands of water conducting tissue in their central stem, but nothing like the large and well organized network of tubes in tracheophytes, or "tube plants". The vascular tissues in the more advanced ferns and "fern allies" are made up of xylem and phloem, which conduct water, nutrients, and food throughout the plant body. We'll look at these tissues in a later lab.
Bryophytes also need a moist environment to reproduce. Their flagellated sperm must swim through water to reach the egg. So mosses and liverworts are restricted to moist habitats. There are no mosses in the desert. But mosses are surprisingly resistant to drying up, and can survive under very harsh conditions. Mosses are the most abundant plants in both the Arctic and the Antarctic. Asexual reproduction in bryophytes is accomplished by fragmentation or by tiny vegetative "sprouts" called gemmae, which form in special little structures called gemmae cups.
Mosses and liverworts are lumped together as bryophytes, plants lacking true vascular tissues, and sharing a number of other primitive traits. They also lack true stems, roots, or leaves, though they have cells that perform these general functions. The leafy green plant that we see when we look at a moss or a liverwort is really the gametophyte, which is the dominant stage in all bryophytes. The sporophytes of bryophytes do not have a free-living existence. They grow directly out of the fertilized egg in the archegonia, and remain dependent on the parent gametophyte for their nutrition.