Do two dishes per student. Replace the cover of the petri dish and wrap with parafilm. The parafilm will stretch to seal the dish. Place the vessel under lights for 16 hours per day if possible. Do not put cultures in direct sunlight, but make sure the area where they are placed is well-lighted by fluorescent bulbs.
Growth is slower at lower temperatures.
Look for small green shoots forming on or near cut surfaces. It may take 2-3 weeks or more before any visible evidence of new growth is noticeable. You may need a microscope to see these structures as they begin to grow, but after 5-6 weeks, they should be visible to the unaided eye. If a sterile environment was not maintained, contamination will be obvious within 3 to 4 days. Materials contaminated by fungus will have a fuzzy growth on them, whereas material contaminated by bacteria will have slimy growth on them.