Studies of ectomycorrhiza can contribute to elucidation of fungal relationships (Agerer et al., 1990; Agerer, 1991a). Ectomycorrhiza structures consist of fungal tissues, the arrangement and organization of which can be used to describe fungal species in the same way as any other taxonomically suitable feature. Their characteristics are well conserved (Agerer et al., 1990). As ectomycorrhiza formed by different fungi are structurally distinct (Frank, 1885; Chilvers, 1968; Voiry, 1981; Agerer, 1987-1990), especially with respect to their rhizomorphs (Ogawa, 1981; Agerer et al., 1990), differences between them in nutrition and growth-promoting efficiencies can be expected. Some studies have already confirmed this assumption (Duddridge et al., 1980; Read, 1984; Chu-Chou and Grace, 1985; Kammerbauer et al., 1989). Thus anatomical studies of ectomycorrhiza can provide important information with respect to their physiological capabilities.

It has also been shown that there can be species-specific differences in ability to colonize roots, depending upon age of individual trees or stands (e.g. Fleming, 1983). It is also known that application of fertilizer (Alexander and Fairley, 1983; Brand and Agerer, 1988) or natural flooding events (StenstrĂ´m, 1990) can influence ectomycorrhizal structure. Furthermore, it has been shown that some ectomycorrhizal fungi can grow their hyphae within the rhizomorphs and ectomycorrhiza of other fungi (Agerer, 1990a, 1991a), suggesting that these ectomycorrhizal fungi can influence each other with respect to plant nutrition and with respect to their fruit body formation.

A large number of physiological, ecological and taxonomic studies on ectomycorrhiza have indicated that different species of ectomycorrhiza behave differently in several respects. For this reason alone, comprehensive characterizations of ectomycorrhizal structures are required urgently, so that recognition of naturally occurring types can be achieved.

As early as the end of the last century some authors had characterized ectomycorrhiza to a high standard. Very informative drawings of ecto-mycorrhiza of Castanea sativa were published by Gibelli (1883) and of Fagus sylvatica and Carpinus betulus by Frank (1885). These authors made detailed drawings of the surface views of plectenchymatous and pseudoparenchymatous ectomycorrhizal mantles. For some time after this it was apparently forgotten that such surface views and other plan views of mantles show important features. It was not until the 1960s that such techniques were used again by Chilvers (1968), Zak (1969) and Fontana (1962). Other researchers made tangential sections through mantles (e.g. Haug et al., 1986). Without doubt, however, plan views of different mantle layers are more informative and are easier to prepare and to interpret than are tangential sections. However, if the mantles are very dark, tangential sections are appropriate.

Early studies of the internal organization of rhizomorphs of ectomycorrhiza and of ectomycorrhizal fruit bodies were made by Bommer (1896), Masui (1926a,b) and Melin (1927). Compilations of different types are given by Ogawa (1981) and Agerer et al. (1986, 1990). The first comprehensive introductions to methods for the characterization of ectomycorrhiza were provided by Trappe (1965) and Zak (1973). Only brief remarks by Wilcox (1982) on the characterization of ectomycorrhiza are included in the more recent book, Methods and Principles of Mycorrhizal Research, edited by Schenck (1982). As ectomycorrhizal characterization has progressed considerably over the last 10 years, the updated compilation given in this chapter is intended to facilitate anatomical research on ectomycorrhiza.

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