Ellen wrote:
I've seen these from time to time in my garden. This one, if I'm not
mistaken, looked like it was *attached* to a withered ivy leaf.

I cut it open to see what was inside. Fascinating ... what is it?

TIA

You have the dreaded Marphistes Gall. It is caused by the Marphistes
Mite which mates and lays its eggs in the spring. The plants attempt to
heal themselves by making a "gall" around the egg mass.

Muriatic acid usually proves to be an effective cure, but in this case
stronger measures are required. Go to your nearest fertilizer
wholesaler and beg, buy or steal about a kilogram (about 2 pounds) of
ammonium nitrate. Avoid prills if at all possible, although they will
work in a pinch. When you get home put the ammonium nitrate in a large
baking dish. Mound it up in the baking dish and make a depression in
the center, just as if you were going to bake a cake. Pour in about 1/2
cup of diesel fuel and start mixing the fuel with the ammonium nitrate.
Continue to knead the mixture and add diesel fuel as necessary to
obtain a doughy mixture.

Shape the resulting mixture into a ball about the size of a small
cantaloupe. Before it hardens, be sure to use a pencil or similar
object to poke a fuse hole in it just large enought to hold a small
firecracker. Set your ball out in the sun until it dries completely.
When your mixture has cured, insert a small firecracker into the fuse
hole and use a small dab of putty, spackle or similar substance to hold
the firecracker in place and to fill any voids.

Light the firecracker fuse with a match or lighter and you will see
results immediately.