Joe, a mentor pollen is pollen that which is used to make a pod parent's reproductive system more receptive to a distant partner that it would normally not accept. Usually a mentor pollen is closely related and is one the pod parent likes and the style and ovules become stimulated. Without this stimulation, distant incompatible pollen grains might not be able to travel and survive through the style tube. And if they did make it, the ovules most likely wouldn't accept them. So to make that all possible (at least theoretically), a likeable (mentor) pollen is mixed with the distant unlikable pollen and a mixed seed pod will develop. A mentor pollen sort of tricks the pod parent's reproductive system into thinking everything is great while the distant villain pollen sneaks in and pollenates right along with it. It would be nice if that's all there was to it with Trumpet XX Maragons but it ain't quite all that simple.
