​The radial growth of mycelium can be easily demonstrated with minimal contamination using sclerotia of Rhizoctonia solani cut from the surface of infected potato tubers. This technique does not require aseptic technique and is unlikely to provoke any allergic reactions. Tubers with sclerotia of R. solani (figure 1) can be purchased at most grocery stores. Students cut several sclerotia from a tuber with a scalpel or razor blade, with as little potato tissue as possible, and place them on water agar with forceps. The septate mycelium with its characteristic right-angled branching will grow from each sclerotium across the water agar in 4 to 7 days at room temperature (figure 2). The hyphae can be clearly observed at 200x magnification when the culture plate, with its lid removed, is placed directly on the microscope stage. Because the agar contains no nutrients, there is usually minimal growth of bacteria or other fungi. Rhizoctonia solani will not sporulate under these conditions. If students take the culture plate home with them, they can observe the mycelial growth over time and observe the hyphae microscopically at the next class meeting.​