For some reason, crossbreeding fungi is one of the main quests in this game. You've taken charge of it along with Apoc, since Mariyam and Zevvie don't seem that interested. The way it works is you collect spores to bring to your fungorum and your mycologer helps you experiment with different crosses. From Mariyam's poem hunt it seems like you're supposed to be breeding for size and internal complexity. To be honest you're getting so good at the size part that your fungorum won't be enough to hold mature specimens much longer. But you bet your mycologer would faint with joy if you moved the fungorum up here.
Come to think of it, so would the manifest balancer who keeps your village the same weight as its sibling on the other half of the scale.