Picture your reed basket as a rectangle with the short sides stitched together (a cylinder). Add a circle on one end (the base). What do you get when this object deteriorates? After 7,000 years, probably a rather tattered rectangle.
I suppose it could be the long sides of the rectangle that are attached, for an elongated rather than stubby cylinder.
Picture myself in a reed boat, on a river, with short sides stitched up, and a circular base...