We seldom see most of the living parts of a fungus. They lie
concealed beneath the surface of its substratethe soil,
a tree, a loaf of bread, or an orange. All fungia mould,
yeast, mushroom, or a relativeis a mass of fine, branching
threads or tubes, called hyphae
(singular: hypha), forever spreading outwards in their
quest for food.
The whole diffuse mass of hyphae is called a thallus
(plural: thalli, mycelia). Unlike a plant or animal,
the body of a fungus is not divided into tissues or organs such
as leaves, roots, or a nervous system .