In Lactarius the pleurocystidia are of two major types: macrocystidia and pseudocystidia (in our terminology) with an intermediate type intergrading with pseudocystidia (see subgenus Piperites). Pseudocystidia, as the term is applied by some authors, refers to a cystidium which is the termination of a lactiferous hypha and which projects into the hymenium. Pseudocystidia, as we define them, apply to the filamentous elements normally occurring in the Lactarius hymenium embedded or with only the tip projecting slightly. Their length is about that of the basidia or occasionally slightly longer, their diameter about 2-4 u, and in outline they may be straight, crooked, or, toward the apex, variously contorted. In most, the cystidium is refractive in KOH and the content may be granular, globular, or homogeneous. When embedded in the hymenium these cells are often very difficult to locate, and we do not attach much taxonomic importance to them in the recognition of species because nearly all species have them. They are, rather, a generic character. We do not regard the chemical nature of the content of pseudocystidia as revealed by empirical tests with dyes as a factor in the definition of cystidia per se; rather, it is a separate category entirely, one associated with other features of the basidiocarp such as the latex, and deserving of equal ranking with cystidia and latex in systematic work. Macrocystidia. As we define them here, they are the prominent pleurocystidia of the Lactarius hymenium. They measure up to 130 X 18,u as the upper range for the genus, but at the small end of the range intergrade with pseudocystidia. At first they are often cylindric in shape but soon become narrowly clavate, then subfusoid, finally becoming aciculate to lanceolate or fusoid.
