Chapter Summary

1. Members of the Plant Kingdom have a cuticle and produce their gametes and spores in multicellular organs surrounded by a sterile jacket of protective cells. Their zygotes develop into embryos; and tissues specialized for photosynthesis, conduction, support, anchorage, protection, and reproduction are produced.

2. Cell plates and phragmoplasts appear when plant cells divide. Outside of the Plant Kingdom, these occur only in certain green algae. The similarity in pigments, food reserve (starch), and occurrence of cell plates suggests a common ancestor for the green algae and plants. The Plant Kingdom includes three phyla of bryophytes and several phyla of vascular plants.

3. Bryophytes (liverworts, hornworts, mosses) occur in highly varied and also very specific habitats.

4. Water is essential to bryophyte reproduction. Most water is absorbed directly through the plant surfaces.

5. Liverwort gametophytes with flattened, dichotomously forking thalli are common, but about 80% of the liverwort species are "leafy." Liverworts have distinct upper and lower surfaces, with one-celled rhizoids that function in anchorage on the lower surface.

6. A Marchantia thallus has a central lengthwise groove along its upper surface and is chambered, each chamber containing chlorenchyma cells and having a surface pore. Rhizoids and scales arise from the thallus base.

7. Marchantia reproduces asexually by means of gemmae produced in surface cups and by thallus fragmentation.

8. Marchantia reproduces sexually by means of eggs and sperms produced in archegonia and antheridia on archegoniophores and antheridiophores that arise from the thallus.

9. The zygote develops into a sporophyte that is anchored to the archegoniophore by a foot, from which is suspended a capsule connected to the foot by a seta. Sporocytes in the capsule undergo meiosis, producing spores. Diploid elaters that aid in spore dispersal do not undergo meiosis.

10. The calyptra and other membranes protect the spores until they are released as the capsule splits; the spores may then develop into new gametophytes.

11. "Leafy" liverworts have two rows of overlapping "leaves" and frequently a third row of "underleaves" not visible from above. The "leaves" often have lobes that retain rain water.

12. Hornworts have one chloroplast with pyrenoids in each cell, and they resemble liverworts in their gametophytes. Their sporophytes are hornlike and have a meristem above the foot. Hornwort thalli have pores and cavities filled with mucilage, where cyanobacteria often grow.

13. Asexual reproduction in hornworts is by fragmentation. Sexual reproduction involves archegonia and antheridia produced in rows beneath the upper surface of a thallus. The tip of the hornlike sporophyte splits vertically, releasing the spores.

14. A moss gametophyte consists of an axis to which "leaves" are attached, with rhizoids at the base. The "leaves" are haploid and have no mesophyll, stomata, or veins. Water is absorbed primarily directly through the plant surfaces.

15. Multicellular archegonia and antheridia are produced at the tips of "leafy" shoots. Each archegonium has a cavity, the venter, containing a single egg and a neck through which a sperm gains access to the egg. Sperms are produced in antheridia.

16. After fertilization, the zygote grows into an embryo that is attached to the gametophyte by an embedded foot. The sporophyte developing from the embryo consists of a capsule and a seta. A calyptra derived from the gametophyte partially covers the capsule. Sporocytes in the capsule undergo meiosis, producing spores that are released through the teeth of the peristome, a structure at the tip of the capsule.

17. An operculum that falls off when the spores mature initially covers the peristome and protects sporocytes and spores. When moss spores germinate, protonemata with "leafy" buds develop. The buds grow into new gametophytes.

18. Mosses may be pioneers, along with lichens, on bare rocks. They are indicators of soil calcium, salinity, and acidity. Mosses are not generally edible, although a few are grazed in arctic regions. Some mosses are used for packing material, but the most significant use is that of peat mosses for soil conditioners. Peat mosses can absorb and retain large amounts of water, and their natural acidity gives them antiseptic properties. Peat deposits, from peat mosses that flourished in past eras, are used for fuel and also as a soil conditioner.