Ambassador Seeds were first documented about 150 Earth years ago. They occur about once every 400 days if the trees remain healthy. Natural seed swaps occur between pairs of seeds that (we now know) dropped simultaneously from healthy trees in paired sphere. When each seed was touched by species in sphere the swap occurred - sending an "ambassador" from each sphere to the paired sphere.
Location of the swap is defined by the locations of the pairs of seeds. After the first swap the seeds recharged quickly - allowing for a quick return. "First meetings" were intense but naturally short (it was quite a surprise for both the Mofang and us.) Over time the seeds required more time to recharge - producing longer visits between species.
Everyone who arrives is familiar with the Collector Seeds. The bright light that we were all drawn to right before the event that brought us here is a Collector Seed. What new arrivers may not be aware of is that these seeds (like all seeds) come in pairs. When the Tree drops a Collector Seed on the ground it signals that its twin has begun its quest for a new being. That search may take hours or it may take years. When an appropriate situation (unnatural threat of death?) is found, the seed activates and swaps a smaller (but varying sized) sphere from Earth (or whatever appropriate home world) here to Hunrath.
As Hunrath became more populated we would watch for a newly dropped Collector Seed, collect it, and place it in the entry canyon area. This allowed us to provide a more predictable entry experience for new arrivers, and provide a single area to collect any resources that may have come along with the new arriver.
Unlike Ambassador Seeds (and Mother Seeds?), Collector Seeds do not seem to survive -- the inner core is spent, leaving only the lifeless outer husk.
(Postulated but unverified) First suggested by Alima Hamsa (2232BH), the notion of Mother Seeds extrapolates the behavior of the lesser seeds to a super-seed. She posited that the process that actually "created" the paired spheres was similar to all other swaps, but on a much grander scale.
The idea is that two seeds (from a Mother tree?) were scattered on the "galactic winds" to "find" appropriately similar environments. When matches were found, some process was triggered that swapped large portions of landscape between vastly different worlds. Alima further noted that the Trees' locations in the center of the spheres suggested that the Trees grew from these Mother seeds.
Because of the similarities, it has been conjectured that re-swapping the entire environmental spheres might be possible with a larger scale version of the Ambassador Seed machine.