Glans is singular, glandes is plural. Weird, but that is Latin for you. In any case, making glandes for a trebuchet would be a waste of time, in my un-humble opinion. Glandes are intended to be slung so that they spin like a rifle bullet. Every trebuchet I have seen, would impart a backspin to the load. The specialized shape of the glans were therefore wasted. I do not know if an onager would put any spin at all on its load, so again, no advantage.
The "dough" of which Siguy wrote, is just a mix of flour, water, and salt. A recipe was posted by a member by name of Jareth, in
this topic
. I made an "Indian war club" out of this stuff and a piece of a broom handle, when I was a kid. I eventually threw the club out, about eight years later. It was still in good shape. However, I lived in a dry climate; I think I remember someone here saying that in moister climes, the stuff tended to start molding after a year or three.