Amyloid (mycology)

In mycology a tissue or feature is said to be amyloid if it has a positive so-called amyloid reaction when subjected to a crude chemical test using iodine in either Melzer's reagent or Lugol's solution, producing a black to blue-black staining. The term "amyloid", meaning "starch-like", refers to the fact that starch gives a similar reaction, also called an amyloid reaction. The test can either be on microscopic features, such as spore walls or hyphal walls, or the apical apparatus on an ascus, or be a macroscopic reaction on tissue where a drop of the reagent is applied. Negative reactions, called inamyloid or nonamyloid reactions are for structures that remain pale brown or clear. A reaction producing a deep reddish to reddish brown staining is termed either a pseudoamyloid reaction or a dextrinoid reaction.