ABSTRACT
With the exception of the yeast fungi, the large majority of fungi are composed of microscopic tube-like structures called the hyphae (sing., hypha). The hyphae spread and penetrate into substratum such as leaf litter, a fallen log, herbivore dung, or an artiœcially made agar medium. A hypha is shaped as a cylindrical tube with an average diameter of 4-6 μm and has a tapering tip that branches subapically (Figure 1.1). Each branch has a tip of its own. By iteration of this hyphal modular unit, a radially expanding mycelium is formed (Figure 1.2). At places, the branched hypha is bridged by short lateral outgrowths, bringing the entire mycelium into a protoplasmic continuity. The mycelium spreads over and penetrates into the substratum, secreting digestive enzymes that decompose the polymeric constituents of the substratum and absorbs the solubilized carbon, nitrogen, phosphorus, potassium, and sulfur compounds for its growth. This mode of fungal growth is inferred from examination of cultures grown on nutrient medium solidiœed with agar and based on observations of fungi growing in litter and in liquid-shake cultures wherein the mycelium grows as dispersed mycelium or assumes the outline of spherical pellets.
