I've been told they are insect-polinated (by a commercial vendor of Asian seeds who offers many brassicas).
He warned me they should be grown ONE THIRD OF A MILE APART to ASSURE no cross-polination (his idea of the foraging range of some insect pollinators). I thin k he is being very careful!
>> from another plant
That, I don't know. However, you could bag the branches you want to keep clean, then one night after the bees are asleep, cover everything ELSE with row covers, well-battened-down.. The next morning, un-bag only the branch you want pollinated.
