In vivo observations of the origin of native defects in cotton hairs were carried out during their development in unopened cotton bolls. It is shown that the formation of these structural defects is related to features of their packing inside the cotton bolts during the formation of the boll segments. A mechanism explaining the origination of these morphological defects is proposed. It is based on the hydrodynamic properties of the cytoplasm at the sites of bending in developing cotton hairs.