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1,700?

2,300?

develop from branching rhizomes. The leaves may be whorled or in a tight spiral and are rarely more than 1 centimeter (0.4 inch) long. Adventitious roots, whose epidermal cells often produce root hairs, develop along the rhizomes.

Reproduction

At maturity, some species of ground pines produce kidney-bean-shaped sporangia on short stalks in the axils of specialized leaves. Such sporangium-bearing leaves are called sporophylls. In other species, the sporophylls have no chlorophyll, are smaller than the other leaves, and are in terminal conelike clusters called strobili (singular: strobilus). In the sporangia, sporocytes undergo meiosis, producing spores that are released and carried away by air currents. The spores of some species germinate in a few days if they land in a suitable location, but spores of other species may not germinate for up to several years.

After germination, independent gametophytes develop from the spores. The gametophytes vary in shape, some

Zygotes And Fungi Native
Figure 21.3 A. Lycopodium cernum, a club moss native to the tropics. B. Lycopodium obscurum, native to northern and eastern North America.

resembling tiny carrots. The gametophyte body usually develops in the ground in association with mycorrhizal fungi. Some gametophytes, however, develop primarily on the surface where the exposed parts turn green. All types produce both antheridia and archegonia on the same gametophyte that, in some species, may live for several years. Since the sperm are flagellated, water is essential for fertilization to occur.

Zygotes first become embryos with a foot, stem, and leaves and then develop into mature sporophytes (Fig. 21.4). If the gametophyte is underground, chlorophyll does not develop in the young sporophyte until it emerges into the light. Several sporophytes may be produced from a single gametophyte. A number of ground pines also reproduce asexually by means of small bulbils (bulbs produced in the axils of leaves), each of which is capable of developing into a new sporophyte.

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