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.
Lateral, or secondary, meristems, consist of the cambium and the phellogen (also known as cork cambium). These are tissues in the stem, branches and roots that generate other tissues via mitosis. These tissues participate in the secondary growth of plant, that is, in the thickening of the stem, branches and roots.eristems are the tissues that produce plant growth, and are the origin of all other tissues. They are formed of undifferentiated cells with an intense cell division rate. Meristems are classified as primary meristems and secondary meristems.