1. Created By: Kyana Pereira & Sindy Morales March 11, 2011 Period 08

2.  Woodiness is one of the most important and noticeable stem distinctiveness.  These plants are created with thick cell walls that sustain the plant body.  Woody plants include trees, shrubs, and vines.  Woody plants dominate the vegetation wherever conditions are favorable for plant growth.  Their large, permanent stems and stable root systems place their leaves in position to capture most of the incoming light energy.  The woody habit has been independently acquired in various divisions of the plant kingdom in the past.

3.  Today only the three divisions of gymnosperms and the anthophyta aretruly woody, because of their scattered, closed vascular bundlesmonocots ca  In dicots a small apical meristem can give rise to a massive treebecause the bundles retain active cambium which can expand thediameter of the stem.  Tree-like monocots such as palms have a massive apical meristem thatgenerates the full width of the stem immediately form wood.  The vascular cambium derives from the procambium which in the stemsof dicots persists between the phloem and xylem of the bundles and asinterfascicular cambium.  In the root the cambium arises partly in the pericycle and partly in thearches between xylem and phloem.

5.  Herbaceous plants have plant stems that are smooth and nonwoody.  These plants do not produce wood as they grow.  Examples of these plants are dandelions, zinnias, petunias, and sunflowers.  In the mature root the epidermis has lost its root hairs, the cortex is greatly enlarged and serves for food (starch) storage, and the central stele is surrounded by the endodermis.  Each cell in this layer is suberized in a (Casparian) strip around the radial walls initially and later over its whole surface.

6.  Inside the endodermis are a few layers of cells that remain meristematic, then the phloem and finallythe xylem which is often arranged in a band or cross.  The root apical meristem does not branch.  Roots continue their exploration of soil space by developing new apical meristems from the pericycle.  The new roots break through the cortex as they grow.  Although they are not as diverse as shoots, roots are sometimes modified for special purposes,particularly food storage.  Some of our "root crops" are really stems but carrots, parsnips and sweet potatoes are roots.  In dicots such as sunflower each bundle consists of phloem on the outside and xylem on the inside ofthe stem.  There are usually some fibers associated with the bundle which can be in a cluster outside the phloemor a sheath around the whole bundle (or both).  Across the middle of the bundle is a band of small cells which are capable of cell division. Thiscambium may extend across the pith rays between the bundles when it is called interfascicularcambium.  In monocots such as corn the bundles are scattered, and contain xylem (inside) and phloem (outside) -there are fibers around the outside and the large air-filled cavity in the mature bundle from destructionof the first formed xylem and phloem.  There is no cambium and certainly no interfascicular cambium.