Hypha

From Freepedia

A hypha (plural hyphae) is a long, branching filament that, with other hyphae, forms the feeding thallus of a fungus called the mycelium. Hyphae are also found enveloping the gonidia in lichens, making up a large part of their structure. A typical hypha consists of a tubular wall, usually made of chitin, which surrounds, supports, and protects the cells that compose a hypha. For most fungi, a cell within a hyphal filament is separated from other cells by internal cross-walls called septa (singular septum).

Some forms of parasitic fungi have a portion of their hyphae modified to form haustoria that are able to penetrate the tissues of a host organism. Similar, yet mutualistic forms of penetrating hyphae are called mycorrhizae and are important in assisting nutrient and water absorption by plants.