The Mycelium and Substrates for Growth

Abstract

The vegetative body of most saprophytic fungi is the mycelium; only some members of the Chytridiomycetes and yeasts are non-mycelial. The unit of the mycelium is the hypha, which is typically filamentous except under abnormal physiological conditions. More diverse shapes and forms of hyphae, however, are to be found in vegetative survival structures and in macroscopic reproductive bodies. Hyphae are on average about 5–6 |xm in diameter and grow by wall extension at the tip. The glucan polymers of the fibrillar components of the hyphal wall are elastic and are no hindrance to the stretching process that is an essential feature of forward growth. The actual region of growth is a few micrometres behind the tip, the very tip of the hypha being non-extendable and forming a resistant shield that enables the hypha to penetrate into solid substrata. With the exception of the Oomycetes and certain ascomycete yeasts, the hyphal walls of all other fungi contain small amounts of chitin. This is a hard polymer synthesized from N-acetyl glucosamine and is non-elastic but adds strength to the wall.