What to observe and how to do it?
Taking spore prints
Iron sulfate (FeSO4)
Potassium hydroxide (KOH)
Tissue and structure
The term cystidium, in its broadest sens, has been applied to almost every type of sterile element of the lamellae and of the outer layers of a carpophore which is morphologically or chemically different from the other elements. According to its position on the carpophore or depending on certain morphological or chemical features, several specific terms are applied to classify the cystidia. According to their place on the carpohore, their morphology, their ontogeny or the properties of their contents, cystidia have received different names, the interpretation of which can differ significantly from author to author. A detailed survey of cystidial terminology will be publsihed elsewhere.
In the following discussion, the term cystidium refers to the "typical" cystidia of Russulaceae, i.e. the macorcystidia sensu Romagnesi (pseudocystidia sensu Singer).
A second type of sterile element exists near the edge of the lamellae and will here be referred to as "marginal cells" (Fig. 9). These marginal cells occur on the edge of the lamellae of many tropical Russula and Lactarius (less so in temperate regions) and they resemble the terminal elements of the stipiti- and pileipellis with which they form a continuous layer. This type of element has been named very differently by different authors.
In Aphyllophorales, cystidia, like basidia, have received more attention and have been described in more detail than for Agaricales. Making detailed drawings of the sterile hymenial elements of every specimen makes one soon realize that the variation and the diagnostic or taxonomic value of cystidia of Russula is much greater than the existing studies suggest.
Just as for the basidia (Buyck, 1991), the present study of cystidia results principally from a doctoral thesis on African Russulae (Buyck, 1989), but preliminary observations on some Russulae from other parts of the world suggest that the results can be extrapolated to the entire genus. As precise illustrations of sterile hymenial elements do not exist for most non-African Russula-species, comparison with the latter stays difficult.
Hymenial cystidia of Russula are usually described as cilindrical or fusiform. The difficulty of expressing precise morphological variation for cystidia results once again from the hardly accurate descriptive terminology which is available. Just as for basidia, an illustrated and statistically-based series of cystidium types should be used as a reference for accurate description purposes. Fig. 10a represents some examples of different types of cystidia in tropical, mainly African, Russulae. When comparing these illustrations with Fig. 10b, which represents a typical pseudocystidium of Lactarius, it is clear that the term pseudocystidium is hardly appropriate for the cystidia of Russula. The absence of these typical pseudocystidia in the hymenium of Russula-basidiomes is a constant feature and a good difference with Lactarius (see Buyck, 1988; Buyck & Schoonackers 1986, 1987a, 1987b; Buyck & Van Nieuwenhove, 1987). A more detailed account of cystidial morphology will be provided in future, when the author has studied more collections. At present, it is suggested that the recognition of different cystidium types should take the following features into consideration:
A general feature of Russula-species that possess cystidia on the edge of the lamellae, is the fact that these marginal cystidia are smaller (fig. 11) and sometimes morphologically different (fig. 12) from the cystidia on the sides of the lamellae. I will not discuss now whether the term cheilocystidia should be used for these marginal cystidia, but it needs to be emphasized that similar morphological gradients are common on other parts of the basidiome. In the centre od the pileus, for example, pilocystidia are distinctly smaller and sometimes morphologically slightly different (esp. towards the apex) than the pilocystidia near the pileus margin.
A very interesting feature, which has never been studied in detail for Russula, is the number of cystidia. This can esaily be estimated by counting the cystidia on a limited and easily recognizable surface-area (a perfect solution is to count the cystidia which can be seen within the rectangle delimited in many types of photographic oculars). For easy comparison, the number of cystidia per mm² could then be calculated. Becaues of the number of cystidia increases towards the edge of the lamellae in those species that have no marginal cells, a safe distance of 400 µm away from the edge must be respected when counting cytidia.
From cystidia counts in more than 150 Russula species, I established 6 categories (only 4 in Buyck 1989) for cystidia numbers:
Some species may fall in two categories when the number of cystidia per mm² is close to either the upper or lower limit of an abundance class. The intraspecific variation, however, appears to be low enough to fit easily in one single class (usually variation does not exceed 500 units per mm²).
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