Illustration of the stages in the lifecycle of a Basidiomycetes fungus. In the vegetative asexual stage (orange arrow), the fungal mycelium germinates from basidiospores (bottom right). Each mycelium cell contains a single nucleus. At left, two mycelia have fused, and the cells now contain two nuclei. A mushroom fruiting body grows the mycelium. Within the gills of the mushroom are basidia, specialised reproductive cells. During the sexual stage of the life-cycle (green arrow), nuclear fusion occurs in each basidium, then meiosis, to produce four basidiospores (blue and green), which are released into the air and will germinate as mycelium, starting the cycle again.