Definition of "sphaerocyst"

Russulaceae is distinguished from other families of mushroom-like fungi with gills by the presence of cells (swollen hyphae called sphaerocysts) and filaments which constitute the fruit bodies and can be observed under the microscope in the gill trama and other parts. All other families lack sphaerocysts.

1996, Mark Brundrett, Working with Mycorrhizas in Forestry and Agriculture, Australian Centre for International Agricultural Research, page 121

The trama of Russula and Lactarius is termed heteromerous because of the presence of sphaerocysts (globose cells). These sphaerocysts occur in clusters, called rosettes.

1998, Jacob Heilmann-Clausen, Annemieke Verbeken, Jan Vesterholt, The genus Lactarius, Danish Mycological Society, page 17

A trama bearing many of these sphaerocysts is called a “heteromerous” (meaning “made of multiple parts”) trama. The opposite expression for an ordinary trama without sphaerocysts is “homoiomerous trama.”

2010, R. K. Sharma, D, K. Agarwal, 12: Morphotaxonomic Studies of Poisonous Mushrooms, K. G. Mukerji, C. Manoharachary (editors), Taxonomy and Ecology of Indian Fungi, page 192