So, fungal spores are literally everywhere, and the requirements for fungus to thrive seem to be trivially low; give it a moderately humid environment and it’ll grow on a bare concrete wall ffs eating god only knows what; the dust from the air maybe?
Well, and the great outdoors is full of slightly damp places, many of them downright soggy most of the time - and absolutely rife with organic material to snack on.
Where’s the bottleneck? Why isn’t the world a choking fungal hellscape?
Well, one makes you bigger, one makes you small. Of course the one’s mom gives out don’t do anything at all.
Just go ask Alice if you don’t believe that. Preferably when she is at about 10ft tall.