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The analogous structures have similar function or macroscopic structure, but different microscopic structure; for example, no thallus has vascular tissue. In exceptional cases such as the Lemnoideae, where the structure of a vascular plant is in fact thallus-like, it is referred to as having a thalloid structure, or sometimes as a thalloid.
In lichens it refers to the region of the thallus that is free of algae. The prothallus develops from a germinating spore. It is a short-lived and inconspicuous heart-shaped structure typically 2–5 millimeters wide, with a number of rhizoids (root-like hairs) growing underneath, and the sex organs: archegonium (female) and antheridium (male ...
The thallus contains specialised sclerotic cells in its ventral region that serve as conducting tissue, though these differ from true tracheids in both form and function. These sclerotic cells are elongated, thick-walled, dark brown, fibre-like cells with pointed ends that typically occur singly, though occasionally two or three may be found ...
The thallus is in the form of a flat crust closely adhering to the rocky substrate, giving it the appearance of a coating. It grows radially, assuming a rounded, disc-like shape. It is composed of cells arranged in tightly fused vertical rows, with weakly branching. The lower layer of the thallus adheres to the substrate, without forming rhizoids.
Its undifferentiated thallus is an irregular mix of fungal hyphae and scattered photobiont cells, lacking a cortex or any definable layers. [6] [47] Morphologically, it is the simplest growth form. [48] The cell walls of leprose lichens contain chemical compounds which make them hydrophobic, and thus largely water repellent. However, the lack ...
Cells within circular regions within the perithallus lengthen to form sexual conceptacles, [8] leaving long, wefty cells around the walls of the conceptacle. [14] In the male conceptacles of Austrolithon , marginal filaments grow more quickly, bending in over the top of the conceptacle cavity and eventually setting up as distinct filaments that ...
The yeast cells are responsible for the formation of the characteristic cortex of the lichen thallus, and could also be important for its shape. [ 50 ] The lichen combination of alga or cyanobacterium with a fungus has a very different form (morphology), physiology, and biochemistry than the component fungus, alga, or cyanobacterium growing by ...
These regions include a central pith, a surrounding cortex, and an outer epidermis, each of which has an analog in the stem of a vascular plant. In some brown algae, the pith region includes a core of elongated cells that resemble the phloem of vascular plants both in structure and function.