Here's why:

* Meristems are specialized tissues responsible for plant growth. They contain undifferentiated cells that are actively dividing via mitosis to produce new cells for the plant's development.

* Apical meristems are found at the tips of roots and shoots, responsible for increasing plant length.

* Lateral meristems (like the vascular cambium and cork cambium) are responsible for increasing plant girth and forming new tissues.

While mitosis also occurs in other parts of the plant for repair and replacement of cells, the majority of mitotic activity is concentrated in these meristematic tissues.