Like every other living thing, plants also undergo growth in size (length and width). This growth in length is a characteristics of the cellular division that occurs in a region called MERISTEMS. Meristems are those part of a plants that contain tissues whose cells are always young and actively involved in cell division.
The cells in the MERISTEMS called TOTIPOTENT, which are found at the top or apices of root, shoot etc are involved in continual division, hence, the regions they are found visibly undergoes changes in length as cells multiplies in that region.
