There’s a lot of conjecture in this thread so I might as well throw in a couple cents. Mold is saprophytic so it’s more often than not advantageous to grow tow

There’s a lot of conjecture in this thread so I might as well throw in a couple cents. Mold is saprophytic so it’s more often than not advantageous to grow toward larger stationary objects in its environment to eat. The stack of discs deformed the agar gel, the mechanoreceptors on the periphery hyphae detected the tiny deformation and set off a chemical cascade for growth in that direction. What if the substrate is lumpy and harder than agar? The researchers disabled the mechanoreceptors and there was no “mass detection”. If there’s no deformation in the substrate by discs on a hard bumpy surface then I’m guessing those mechanoreceptors won’t detect the mass. So mold uses gradient deformation of mechanoreceptors to move toward possible food sources.