ABSTRACT
This chapter reviews the structure, development and functions of protonemata from data on wild and cultured materials of over 200 different mosses. Protonemata are defined as multicellular filaments with new cells being added either by division of the apical cell or by the formation of side branch initials. This diagnosis includes chloronemata, caulonemata and rhizoids, all three interrelated developmentally but each with a wide range of distinctive attributes, embracing cytological organization, wall architecture, mode of growth and tropisms. Unlike protonemata perturbed by growth regulators, and drugs that affect the cytoskeleton, which revert to normal morphogenesis when transferred to media lacking these agents, hypomethylated protonemata retain their abnormal morphogenesis. The chapter presents what is probably the first comparative account of the morphological diversity of moss protonemata. This new information is then used to assess the possible relevance of protonemata in moss systematics and phylogeny.
