Chapter 13

In spite of penetrating stains and brightfield optics of considerable resolution, definite limits of observation inevitably were reached in traditional cytology. Although the light microscope revealed basal bodies in the spores of watermolds, how did they anchor successfully against the forceful beating of flagella? While the best of optical glass could reveal bivalent rings in presumed meiotic figures, were these truly bivalents, and how did they separate and migrate? These are just two of many questions that cytology with the light microscope could not resolve. At hand was the electron microscope, capable of further resolution and presumably able to suggest answers to these questions that had been so tantalizingly just out of reach. This is not to say that all traditional cytological work on the Saprolegniaceae was untrustworthy; it is to say that it had attained an inviolable limit dictated by certain physical principles of light. The first watermold to be subjected to the preparative treatment necessary for electron microscopy was Saprolegnia ferax, about which Manton and her colleagues published in 1951 and 1952. It was to be some 15 years later -beginning about 1966 -that biologists again applied electron microscopy to the watermolds. In a very real sense, this delayed application of ultrastructural methodology to these fungi proved to be advantageous. The use of the electron beam just to discover organelles and to catalogue them had flared into prominence, and while such work had by no means halted abruptly, it was giving way to interpretive, comparative ultrastructure. Indeed, this approach is encouragingly prevalent among the existing accounts of the fine structure of watermolds. It should hardly be surprising that the burst of elegant electron images published in a short span between about 1966 and 1978 should be differently interpreted on occasion or that faults in preparation should creep into methodology. As we are not experienced investigators in ultrastructure, we cannot choose confidently between what is adequate preparation and what is not. Accordingly, we do not sort out the doubtful bits and pieces, but we do erect signs along the way pointing to differences of opinion or interpretation. Perhaps at some later date, the accumulated knowledge can be analyzed and positive interpretations brought forward. Relatively few members of the Saprolegniaceae have been probed with the electron beam and their inner structures uncovered. Chiefly these have been Achlya ambisexualis [studied by Tontz (Ellzey)]; A. bisexualis (Dargent): A. recurva (Steffens), Aphanomyces euteiches (Hoch and Mitchell); Saprolegnia ferax, Dictyuchus sterile†, Thraustotheca clavata (Heath, Greenwood, and Gay); S. furcata† (Beakes, and Beakes and Gay), (Hagedorn and Weinert), and S. terrestris (Howard and Moore). At least some of these species mentioned are particularly thorough review papers that serve an additional purpose of acquainting the reader with the events and theories of interpretive ultrastructure: Bracker (1967), Beckett et al. (1974), Kubai (1975, 1978), Bartnicki-Garcia and Hemmes (1976), Fuller (1976), and Heath (1976).