The stem is an important part of a plant's body. In ordinary plants, the stem stands upright on the ground, with leaves, flowers, and fruits growing on its branches. At the same time, the stem also serves as a channel for connecting the roots and leaves, transporting the water and nutrients needed by the plant back and forth. Almost all plant stems are upright and grow upward. Regardless of their thickness, length, or hardness, they resemble small round sticks "standing" on the ground. However, there are exceptions. Some plants' stems undergo metamorphosis, taking on bizarre shapes, which are referred to as metamorphosed stems. Although they lose their function of transporting water and nutrients, they acquire other special functions.
The potato is one of the metamorphosed stems. Its aboveground part, like ordinary plants, has an upright stem, but underground it also grows another round stem, which looks similar to the color of the soil and resembles small lumps of earth, hence it is also called potato, Irish potato, or yam egg. The greatest function of this metamorphosed stem of the potato is to create "nutrient warehouses" for the plant. If faced with harsh climatic conditions, although the aboveground part withers and dies, the underground tubers will not perish. Relying on the abundant nutrients stored within, they can survive for a long time. When the climatic conditions improve, the tubers can sprout young shoots and give rise to new plants.
The onion head is also a very special stem, which botanists have given a special name - bulb. Its body is surrounded by many layers of fleshy scaly leaves, as if it were wearing dozens of clothes. These scales not only store nutrients but also protect the young shoots inside the bulb and prevent water loss. There's also the familiar lily, which is a typical bulb plant. Its underground part has a snow-white, lotus-shaped thing, which is its underground bulb. If we peel off the thick fleshy scales on the outside, we will see a tightly protected, disc-shaped, greatly shortened stem.
In summary, many plants, under the natural selection of different environments, develop various bizarre-shaped stems, all with the aim of better adapting to the environment and ensuring survival.