someone sent me gustavia seeds. they looked great and were very fresh, they started to split up, but there came never a sprout. today i cut a few seeds in two and later in several pieces to look how they look inside. there were were no embroys inside them! how is that possible? everything is great with the seeds, they are fleshy and in an excelent condition, but like allready mentioned no embryo (not even a very little one)! i know exactly how an inner seed and embryo looks, i even read the book: seeds: ecology, biogeography, and evolution of dormancy and germination. when they are not polinated, why do they look like well developed seed ?
Can't explain why your seeds look so well developed but obviously they were not pollinated, which resulted in empty seeds. According to http://tomclothier.hort.net/ (under "A note on Seed Viability") "Incomplete pollination results in a high proportion of empty seeds. They look like seeds, but there is no embryo, or one which is only partly developed. Some plants require 15 to 20 visits to each flower by a pollinator in order to produce a good seed pod or fruit. Even then, the seeds have to be collected after they have fully ripened."
Sorry to hear about the problem you're having. If you still have some seeds left, try putting them in water and plant the ones that sink. I doubt that an empty seed would sink.
We had a bad year here for pine nuts several (6?) years ago. Pinon pines had cones, cones had normal sized nut shells, but shells were hollow, nearly empty. I never heard any explanation of why it happened, but it was pretty wide-spread in this area. Pinons do not depend on insect pollination. It is weird that your seeds appeared fleshy - but it is similar to our pine nut that made empty shells - Usually there is just an empty scale on the cone, similar to blank spots on a corn cob.