This photo comes from microbiology, specifically antimicrobial susceptibility testing. Mold spores spread evenly across the agar plate; then a small well was punched in the center, and an antimicrobial compound was added. As the compound spreads through the agar, it stops nearby fungal growth, leaving a clear "zone of inhibition." A larger zone usually means strong antifungal inhibition.

Top-down view of a petri dish on a black surface. The agar is covered with a fine, tan layer of fungal growth. A small punched well sits in the center surrounded by a larfer, darker, roughly circular zone with no visible growht, about a third of the dish’s width.