Sinningias form tubers, storage organs which preserve the plant in a dormant state through the non-growing season (usually winter for sinningias, but other bulbs such as tulips are dormant during summer and autumn) and give the plant a boost in making new growth in the spring.
Tubers come in many shapes, but the most common is the vertically flattened sphere. New shoots emerge from the top of the tuber, as shown in this picture of Sinningia hatschbachii. Note the beet-red color of the tuber, which is characteristic of this species. Also note the knob on top, like a second tuber sitting above the first one -- several species form such tuber knobs.