Because the concentration of agar and other conditions in the same Petri dish are the same, the diffusion rates of various substances such as nutrients in all directions are equal. That is to say, the substance diffused in the culture dish is round in shape. Plus the colony is round. Therefore, designing the Petri dish into a circle is beneficial to the complete diffusion of experimental substances in the whole Petri dish and to scientific experiments that need to control variables.
2) Considering the durability of equipment and laboratory hygiene:
The circular Petri dish has no edges and corners, so it is easy to clean, and there will be no residues such as experimental flora accumulated in the corners of the Petri dish to cause pollution, which will affect the subsequent experiments. In addition, the usual disinfection methods of Petri dishes are high-temperature methods such as steamer or fire roasting. Without edges and corners, Petri dishes will not break due to thermal expansion and cold contraction.
3) Considering the difficulty of production:
Early Petri dishes were all made of glass, and the round shape was easier to make than other angular shapes, such as square, because the corner position was easily broken or worn when demoulding and cooling.