Colonies of the red- orange fungus Oidium aurantiacum as they appear to the naked eye in the cavities of infected bread. A similar colony cut in two, showing in the red area a thick layer composed of innumerable small spores formed at the end of radiating filaments. The latter are yellowish white. Similar colonies that have grown up completely in the dark, with the result that the red color has not developed. One of the colonies in b seen after exposure to light for one hour.
Color begins to appear and then pigmentation progresses rapidly.
Branching filament, about 150 x. Spore treated successively, under the microscope, with a dilute solution of potassium hydroxide, and aqueous alcoholic solution of iodine, then with gradually more concentrated solutions of sulfuric acis. This acid, which separates parts of the cellulose envelope that contains less nitrogenous substance, results in a blue color turning to purple, which is characteristic of the state intermediate between cellulose and dextrin. Termini of well developed filaments, showing spores and young cells.