Michael,

Certain wide crosses (interspecific or intergeneric) produce seemingly good embryos that don't develop, for a number of reasons, because a growing organism proceeds by chains of different organic reactions with a unique string of intermediates, and a wide hybrid can produce competing chains whose "gears clash". Frequently such embryos can be artificially coaxed to maturity by using the techniques of zygotic embryo culture. This subject was discussed in more detail in the Ways of 'growing' seed from aborted seed pods message thread.

MM

Thanks. I'm looking into that thread.