Some other lycophytes coexisting with the tree lycophytes were small herbaceous plants that resembled modern Lycopodium and Selaginella species. However, the vascular cambium had one major flaw: Pteridophytes also show a transition from simple to complex leaves. Notice the prominent indusia , and the small sporangia peeking out from beneath. Whereas cotton absorbs times its dry weight, dried sphagnum can absorb 20 times its own weight in fluids!
A gymnosperm ovules and seeds develop on the surfaces of specialized leaves and also includes ginkos and cycads. We'll look at these tissues in a later lab. It was less than 15 cm tall, with stems that dichotomously branched. At the apical bud of the stem, or at the apex of a fertile stem, a strobilus forms. There are about , species of vascular plants, grouped in nine divisions. Typical heterosporous life cycle. In some species "side-branches" arise from these nodes.
The Division Psilophyta consists of Psilotum nudum the whisk fern, shown in Figure 11 , a living plant that resembling what paleobotanists believe Cooksonia to have been: The sporophytes are horn-like projections that rise from the gametophyte. Sporophylls may be aggregated into definite strobili, or there simply may be fertile and sterile regions along a stem, the sporophylls resembling vegetative leaves. Farabee at Estrella Mountain Community College. Spores that are wind-borne to shady, moist habitats germinate and yield multicellular, but microscopic, gametophytes, the sexual stage of the life cycle.
Their sexual reproduction is done through spores. Further study supports the status of Psilotum as a true fern that has apomorphically reversed some of its character states so that it superficially resembles the extinct species. The sperm swim in soil water to the open archegonium. In the center of the leaf base you can see the leaf trace, or vein to the leaf. So if Psilotum is a "primitive" vascular plant, then a dicot root haplostele form of protostele is more "primitive" than a dicot stele eustele form of siphonostele. The spore cracks open, exposing the archegonia megagametangia and permitting fertilization by swimming sperm cells. Drepanophycus is a middle Devonian lycophyte from the Northern Hemisphere, also shown in Figure