I'd not heard of Arthur Rex, so scurried off to Google Books to see if I could find out what it means by seeding. I don't think I found what I was looking for, but this is hilarious:

"Sire," said Merlin, "not all women are your kinsfolks."
"Yet," said Arthur, "who might tell, with all the seed my father did broadcast?"
"But," Merlin said, "Uther Pendragon did bed in the main the female issue of churls or defeated paynims, generally virgins of very tender age, as is so often the taste of kings."