There are three general types of 
Meristems in plants.
They are either Apical, Secondary (Branches) or Lateral.
The Root and Shoot Apical
Meristems become defined during Embryogenesis. Secondary
Meristems which give rise to branches arise later in development.
We will explore Lateral Meristems
later. They increase the diameter of their axis and add to the girth of stems and
roots.
The Apical Meristems of Seed
Plants are multicellular. They may function over many years or even centuries
in the case of certain gymnosperms like bristle cone pine and giant Sequoia. They
are said to have Indeterminate
Growth!
Meristems may contain Initials.
These are undifferentiated cells that undergo mitosis at a slow rate. Their
derivative cells continue to divide, but eventually differentiate into one of the three
Primary Tissues.
Root Development
The Root is very conservative in terms of
its evolution. It is designed to penetrate the soil. Consequently, branching does not
occur at the tip, but they arise basipetally (towards the base). Their origin is Internal.
Both of these factors prevent damage to young branch roots.
The root Apex is covered by a Root
Cap which protects the Root Apical Meristem (RAM) and
secretes mucilaginous carbohydrates which act as a lubricant.
Most roots produce Root
Hairs. These occupy a zone that is posterior to the elongation (growth) zone. They
greatly increase the absorptive surface area of the root.
Meristems-1 
are said to have Indeterminate
Growth!