It requires at least 25 Zelkova branches. Deliver them to Biologists Chaegirab. He examines the branches, but sometimes he breaks them, and you have to get a new one. You can onlydeliver a branch every 24 hours.
The Zelkova branches can be found only during the quest, oce you get one in your inventory you can't get another drop. Once you begin these quests the expert mission books quests do not work.