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.
Meristematic cells are generally small and cuboidal with large nuclei, small vacuoles, and thin walls. A plant has four kinds of meristems: the apical meristem and three kinds of lateralâvascular cambium, cork cambium, and intercalary meristem.