Types discussion: Autism (a developmental brain disorder characterized by impaired social interaction and communication skills, and limited range of activities and interests) is the most characteristic and best studied PDD.
A meristem is the tissue in most plants containing undifferentiated cells (meristematic cells), found in zones of the plant where growth can take place. Meristematic cells give rise to various organs of the plant and keep the plant growing.hese secondary meristems are also known as lateral meristems because they are involved in lateral growth. At the meristem summit, there is a small group of slowly dividing cells, which is commonly called the central zone.
As we mature, our bones, skin and muscle all increase in size. Trees do not grow like this. Trees grow by producing new cells in a very limited number of places. These places of cell division are called meristems. Meristems are zones of intense activity. They are where all new cells are formed and where they expand.