Feather These barbules have minute hooks called barbicels for cross-attachment. Down feathers are fluffy because they lack barbicels, so the barbules float free of each other, allowing the down to trap air and provide excellent thermal insulation. At the base of the feather, the rachis expands to form the hollow tubular "calamus" (or quill) which inserts into a follicle in the skin. The basal part of the calamus is without vanes. This part is embedded within the skin follicle and has an opening at the base (proximal umbilicus) and a small opening on the side (distal umbilicus). Hatchling birds of some
Acorus calamus of the fleeting nature of childhood: in the story, Alice picks scented rushes but complains that the prettiest ones are always just out of reach, while the ones she is able to reach fade and lose their scent as soon as they are plucked. The root of the calamus (Tamil vasambu வசம்பு) is cut into disc-shaped beads, and made into bracelets, which are typically worn by newborns for the first few months. A vasambu bracelet is a symbol of a newborn baby in Tamil culture. "A. calamus" and products derived from "A. calamus" (such as its oil) were banned from