Plants and society e levetin and k mcmahon pdf

They are characteristically limited in size and prefer moist habitats although they can survive in drier environments. The bryophytes consist of about 20,000 plant species. Regardless of their status, the name is convenient and remains plants and society e levetin and k mcmahon pdf use as an informal collective term.

Bryophytes exist in a wide variety of habitats. Bryophytes can grow where vascularized plants cannot because they do not depend on roots for an uptake of nutrients from soil. Bryophytes can survive on rocks and bare soil. The life cycle of a dioicous bryophyte. Gametophytes produce haploid sperm and eggs which fuse to form diploid zygotes that grow into sporophytes.

Bryophytes are gametophyte dominant, meaning that the more prominent, longer-lived plant is the haploid gametophyte. The diploid sporophytes appear only occasionally and remain attached to and nutritionally dependent on the gametophyte. Liverworts, mosses and hornworts spend most of their lives as gametophytes. Sperm are flagellated and must swim from the antheridia that produce them to archegonia which may be on a different plant.

Arthropods can assist in transfer of sperm. Fertilized eggs become zygotes, which develop into sporophyte embryos inside the archegonia. Mature sporophytes remain attached to the gametophyte. They consist of a stalk called a seta and a single sporangium or capsule. These are dispersed, most commonly by wind, and if they land in a suitable environment can develop into a new gametophyte.

The main division is between species in which the antheridia and archegonia occur on the same plant and those in which they occur on different plants. These terms occasionally may be used instead of “monoicous” and “dioicous” to describe bryophyte gametophytes. Monoecious” and “monoicous” are both derived from the Greek for “one house”, “dioecious” and “dioicous” from the Greek for two houses. The use of the “oicy” terminology is said to have the advantage of emphasizing the difference between the gametophyte sexuality of bryophytes and the sporophyte sexuality of seed plants. The exact arrangement of the antheridia and archegonia in monoicous plants varies. Hornworts include those bryophytes that are believed to be the closest living relatives of the vascular plants.