The physiology of development in fungi

Abstract

Fungi differ widely in vegetative form and in details of their life-cycles. A few fungi are unicellular but most consist of branched filaments or hyphae. When a fungal spore germinates it gives rise to a germ tube which, under suitable conditions of growth, continues to grow and to branch, forming a mycelium or mass of hyphae. At first the hyphae are more or less similar in structure, but sooner or later according to the species and to the external conditions, changes set in leading to sporulation or to the formation of characteristic aggregates of vegetative hyphae such as sclerotia, mycelial strands or rhizomorphs. With most fungi the first type of spore to be produced by a young colony is asexual. These may be motile zoospores (Figs. 1 and 2)1 as in the Chytridiales, Blastocladiales, Monoblepharidales and most Oomycetes; non-motile sporangiospores (Fig. 3), as in most Zygomycetes; or conidia (Figs. 5 and 6) as in the more advanced Oomycetes and Zygomycetes and in the Higher Fungi. The fungus may usually be maintained through several generations by the production of asexual spores only. Some, the Fungi Imperfecti, lack any trace of a sexual or perfect stage. Most Lower Fungi (Phycornycetes) and many Higher Fungi, however, also produce a second type of spore, usually in response to particular environmental changes, often to conditions less favourable to vegetative growth.