Stem cells are undifferentiated cells. This means they have not yet become specialised, and they can divide to make more cells.
In animals, stem cells are found in embryos. Embryonic stem cells can become almost any type of cell. Adult animals also have stem cells, for example in bone marrow, which make blood cells.
In plants, stem cells are found in meristems. Meristems are at the tips of shoots and roots, and they produce cells that grow into any type of plant cell for as long as the plant lives.
Because meristem cells can make a whole new plant, gardeners can clone plants. Small pieces of cauliflower containing meristem tissue can be placed on a growth medium, where they grow into new cauliflower plants that are genetically identical to the original.