Partial Veil - Structure

Structure

In the immature fruit bodies of some basidiomycete fungi, the partial veil extends from the stem surface to the cap margin and shields the gills during development, and later breaks to expose the mature gills. The presence, absence, or structure of the partial veil is an aid to identification of mushrooms. Some fruit bodies may have both a universal and partial veil, others may have only one or the other, while many lack both types of veils. The partial veil may be membranous or cobwebby, and may have multiple layers. Various adjectives are commonly used to describe the texture of partial veils, such as: membranous, like a membrane; cottony, where the veil tissue is made of separate fibers that may be easily separated like a cotton ball; fibrillose, composed of thin strands and glutinous, with a slimy consistency. Some mushrooms have partial veils which are evanescent, which are so thin and delicate that they disappear after they rupture, or leave merely a faint trace on the stem known as an annular zone or ring zone. Others may leave a persistent annulus (ring). Occasionally, the partial veil adheres to the edge of the cap as shreds of tissue, forming an appendiculate margin.

The partial veil of some species, like this Stropharia ambigua, may form an appendiculate cap margin

The cobweb-like, fragile partial veil of some mushrooms, especially those in the genus Cortinarius, are known as cortinas. The fibrous threads of the cortina often catch the brown spores as they drop, making them visible as fine brown streaks along the stem. Some species of Agaricus, such as Agaricus arvensis, have a partial veil that resembles a cogwheel. Mycologists Alexander H. Smith and Harry D. Thiers, in their 1964 monograph on the bolete genus Suillus, proposed the term "false veil" to account for those species of Suillus that have a "conspicuous cottony roll" of tissue that originates from the cap margin (especially in young specimens) and never becomes integrated with the stem tissue.