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.
Apical Meristems. Apical meristems are the site of primary growth in a plant, and can be found at the root and shoot tips. Here you can find unspecialised cells, which undergo the following sequence to become a functional part of the plant. 1  New unspecialised cells become available at the meristems, the site of mitosis.