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Using a Microscope: The Cap Surface

by Michael Kuo

The cells composing the "skin" of a mushroom's cap can have many different appearances, and it should come as no surprise that mycologists use the differences as taxonomic characters. The sectioning method described and illustrated in Creating a Section to Study will provide you with a way to study the surface of the cap, along with the gills--but if your mushroom's cap is fleshy and large, you may find it easier to simply slice a paper-thin section of the cap surface from a small chunk of the cap.

Comprehensive coverage of the many types of cap surfaces classified by mycologists can be found in Largent et al. (1973; citation here). My intent here is only to introduce you to a few of the basic types. In the illustration to the right, three cellular arrangements are portrayed on the surface of the cap. On the left, a cutis consists of cells that are tangled together and run parallel to the cap surface. In the middle, a trichoderm has cells that are woven together and run perpendicular to the cap surface. On the right, a cellular layer of blob-ish cells is arranged more or less randomly. The term "cellular" is a bit confusing, but only because I have avoided calling mushroom cells "hyphae" throughout this Web site, in order to make my text accessible to a broader audience. Mycologists use the term "hypha," rather than "cell," for fungal cells because they are distinctive and elongated. The "cellular" hyphae we are discussing are an exception, and look similar in shape to many plant and animal cells.

 

A cutis, trichoderm, and cellular layer


In the schematized illustration above, it's easy to see the differences between cell types and arrangements. Things are not so easy under the microscope. For example, imagine trying to tell the difference between a cutis and a trichoderm if you have made a "crush mount" and cannot be certain whether your pressing down on the cover slip influenced the appearance. Now add the fact that there are a gazillion different types of cap surfaces, not just three, and some of them are only subtly different from one another.


Cystidia

Cystidia can be found on the cap surface in some mushrooms (and they are then called "pileocystidia"). Like cystidia on the gills, cap cystidia are diverse; see Largent et al. (1973) for comprehensive treatment. The long, pointy cap cystidia to the right belong to Rickenella fibula, which is covered with cystidia from head to toe.

 

Pileocystidia


Broom Cells

These funky cells are found on the cap surfaces of some mushrooms, particularly in the genus Marasmius, where their presence or absence, together with their shapes and dimensions, can help in the identification process. To me, they look like malformed basidia that wound up in the wrong place. The illustration features the broom cells of Marasmius cohaerens.

 

Broom cells



Gelatinized Cells

The cells on the surface of the cap sometimes appear gelatinized, vague, and permanently out of focus. When you are sure that they really aren't out of focus, you may be looking at the microscopic evidence of a "viscid" (Mycologese for "slimy") or once-viscid cap--and this can be a pretty neat trick for figuring out mushrooms that grew in dry conditions and lacked the sliminess they "should have" displayed more obviously.

 

Gelatinized Cap Surface



Cite this page as:

Kuo, M. (2006, February). Using a microscope: The cap surface. Retrieved from the MushroomExpert.Com Web site: http://www.mushroomexpert.com/microscope_cap.html

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