What to observe and how to do it?
Taking spore prints
Iron sulfate (FeSO4)
Potassium hydroxide (KOH)
Tissue and structure
Microscopic features of the basidiome can roughly be classified into three categories: (1) features concerned with hymenial structures, (2) features of the superficial layers of stipe and pileus (the pellis) and (3) the features of the trama. Maire (1910), in what can be considered as the first important contribution to the study of the most important microscopic features of Russulales, already supplied precise drawings of the most important microscopic features with his descriptions. Unfortunately, the example of Maire was not always followed and we can only deplore the fact that many mycologists do not yet fully conceive the importance of good illustrations. I think, for example, of the many new taxa described by Singer, usually without a single good illustration. I firmly contest Singer's statement that descriptive terms in the genus Russula "are so standardized and so frequently defined that the only form of illustration necessary or desirable in order to improve on the description would be colored plates of the species involved" (Singer 1957: 143). On the contrary, original studies in mycology should always lead to the publication of numerous good and high quality illustrations, especially of the microscopic features! The importance of providing precise illustrations has very recently been demonstrated by Buyck (1990).
Precise illustrations not only add to a better understanding of a description, but sufficient illustrations may also reduce the number of requests for loan of type-specimens, which is a very time-consuming factor in any systematic study and involves an unnecessary risk for the specimens themselves.
For most European species, the monograph of Romagnesi (1967) has partly compensated the need for better illustrations (just try to imagine the utility of this book without the illustrations for spores and pileipellis!). It is my intention to comment on my experience on microscopic features of Russula, in particular on the tropical African and South American species. It is obvious that many useful characters have simply been neglected because of the lack of precision in the present descriptions - especially where features of hymenial structures are concerned. Most descriptions aim too often at identification, not at a full analysis of all possible characters. In spite of Romagnesi's convinction that new microscopic or microchemic characters of taxonomic value were unlikely to be found for Russula, it is clear that more precise observation and especially the careful illustration of all cell-types can supply a whole series of new and useful characters.
Sufficient accuracy can only be obtained through illustrations, not through the use of a descriptive terminology. I think it may, therefore, be very useful to start this series with a few guidelines on how to make better drawings of microscopic features:
Information on descriptive methods can be found in Josserand's magnificent treatise on mycological description and terminaology (2nd ed., 1983), of which there is unfortunately no English translation available.
In the following pages, I am not going to explain once more all general tecniques, nor the advantages of the use of chemicl reagents. The objectives are, firstly, to analyze shortly the taxonomic value and description possibilities fo the currently used important microscopic features and, secondly, to point out some features which are generally ignored or which deserve more attention than they now receive, not because they should enable us to identify certain species more easily, but because these features can teach us more about the evolution and relationships in the Russulales as a group. As said before, most of this series is based on my study of tropical Russulae. Because the same kind of precise observations rarely have been made on Russulae of the temperate flora, extrapolation of my findings to the latter is difficult or sometimes impossible.
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