Growth after the Roots and Shoots are in Position.

An entire plant's final growth cannot be determined; however, its "organs'" can.  How might you ask?  It is quite simple and efficient really; plant have specific cells whose purpose is solely to grow.  These embryonic tissues are called meristems.  Cells in the meristem have two fates: 1) differentiate and divide, or 2) simply keep dividing.  Non-woody plants only have an apical meristem, or a meristem located at the top.  Elongation in an upward direction is called primary growth.  Woody plants have two types of meristems:  apical and lateral.  Lateral meristems are responsible for creating the girth (large trunk) of a tree; this is produced by elongation parallel to the ground (left and right, front and back).

More on Woody Plants.

Primary and secondary (lateral) growth occur simultaneously.  Primary growth occurs in the younger tissue at the tip of the tree; secondary growth occurs in the older tissue away from tips.  This lateral growth creates a new epidermis and replaces the old epidermis and vascular tissue with vascular tissue and dead tissue, respectively.  To skip primary growth and lean about secondary growth, click here.

Primary Growth.

In the Roots.

The root tip is covered by a root cap.  The root cap protects the meristem as it pushes against the soil, partially by secreting a slime whose main component is a polysaccharide.  Growth is concentrated where else but the tip!  There are three areas of cells responsible for successful root growth;  these areas a directly related with the stages of growth:  1) division 2) elongation 3) maturation.

Cell Division.  Here, near the tip cells divide rapidly; however, at the quiescent center cells divide more slowly.

Elongation.  Here, cells grow to about 10 times their original length for the main reason of moving the root tip ahead.  During this stage, the cells begin to differentiate into the protoderm, vascular tissue and ground tissue.

Maturation.  Here, cells finish specializing into the dermis, vascular tissue and cortex.

What are these Primary Tissues of Roots You are Talking About?

Ground.  Mostly parenchyma fills the cortex.  The cortex is between the dermis and vascular tissue and active in mineral uptake.  The innermost layer of the cortex is referred to as the endodermis.  This is a one-cell thick selective barrier surroundind the vascular tissue.

Vascular.  The procambium eventuallly becomes the stele (central vascular cylinder where xylem and phloem mature).  In dicots, the xylem radiate from the center and phloem is the areas inbetween.  In monocots, there is a parenchyma core surrounded by a ring of xylem and phloem, xylem and phloem (alternating)....

Dermal.  This eventually becomes the epidermis.

How do Lateral Roots Develop If It Is a Taproot?

The outermost layer of the stele is an area of hibernating meristematic cells, called the pericycle.  Here is where lateral roots originate.  A clump forms in this area and migrates out through the two processes of mitosis and elongation.

In the Shoots.

Apical meristems are shaped like a dome at the tip of the terminal bud.  It produces primary meristems (protoderm, procambium, ground meristem).  Leafs begin as leaf primordia on the edges of the apical meristem.  Axillary buds mature from isolated areas of the apical meristem outside the leaf primordia.  In a bud, nodes are crowded close together because internodes are not yet elongated.  At this time, most elongation is a caused by that of older shoot areas below the area of growth.

Why Axillary Buds can Grow into New Branches.

Vascular tissue is near the surface; therefore, without beginning deep in the stem, a new branch can "hook itself up" to the internal transport system.

Primary Tissue in Shoots.

There are several strands of vascular tissue in shoots - as opposed to one continuous bundle in the roots.  The part of plant where the shoot and the root merge is called the transition state.  At the transition state several bundles converge (or one bundle diverges depending on your perspective).  Each bundle is surrounded by its own ground tissue composed of pith (the parenchyma core) and cortex.  In the stems of dicots (since it is circular) xylem face pith and phloem face cortex.  In monocot stems the ground tissue is mostly parenchyma but is a large collection of collenchyma beneath the epidermis.

Leaf Tissue Organization.

Leaf is surrounded by the epidermis tightly formed around a bunch of cells.  Around the epidermis is a waxy cuticle that serves as a water barrier preventing desiccation.  This barrier is only broken by stomata (tiny gates into the leaf's gas exchange chamber).  The leaf ground tissue is mesophyll (parenchyma with chloroplasts).  Dicots have 2 pronounced mesophyll regions:  upper and lower.  The upper layer is composed of one or more layers of palisade (column-shaped) parenchyma.  The lower layer is the spongy mesophyll that interacts in gas exchange.

The Leaf Vascular System.  Leaf traces (branches of the bundles in the stem) travel through the petiole.  They support the leaf mesophyll cells and bring the xylem and phloem close to areas of photosynthesis for more energy efficient transporting of food.

Next:  "Shoot Anatomy."