The basidia are 15 – 25 × 3 @.@ 5 – 5 @.@ 5 µm and have a slim , club @-@ like shape . Each basidium feature four sterigmata , each of which bear one spore . The spores ' shape is slimly ellipsoidal or cylindrical . Their surface is smooth and their walls are thin . Although they are colourless and hyaline , the spores are amyloid , meaning they will turn bluish or purple when stained with Melzer 's reagent . This characteristic differs from other very similar species , and this gave the genus its name .