A single page from a series on identifying textile fibers by microscope and chemical tests. It describes the twisted, hollow, ribbon-like form of cotton fibers and how they swell and dissolve in ammoniacal copper hydroxide (reagent No. 4). It also introduces bast fibers (flax, hemp, jute, ramie), the role of lignin and retting, and the basic equipment for fiber testing. Two microscope figures show untreated and treated cotton.