The stem
Feb 23, 2016
The stem
The Stem
• A stem is one of two main structural axes of a vascular plant.
Stems• In most plants stems are located
above the soil surface but some plants have underground stems
• A stem develops buds and shoots and usually grows above the ground. Inside the stem, materials move up and down the tissues of the transport system.
• The term shoots is often confused with stems; shoots generally refer to new fresh plant growth and does include stems but also to other structures like leaves or flowers
Parts of the Stem • The stem is normally divided into nodes and
internodes.• Main stem: the most important one in the plant• Secondary stem: grow from the main stem• The nodes: hold buds which grow into one or
more leaves, flowers, cones or other stems etc. • The internodes: distance one node from another. • Buds: are the responsible for plant growth;
either new stems, flowers or leaves.• - parts of the buds• Main terminal bud: is in charged of the upwards
growing of the plant• Secondary terminal bud: come out from the tip
of secondary stems, they make the secondary stem grow
• Lateral buds: are placed on the stem nodes, leaves and flowers arise from it
Functions • Stems have four main functions which are:
• Support for and the elevation of leaves, flowers and fruits. The stems keep the leaves in the light and provide a place for the plant to keep its flowers and fruits.
• Transport of fluids between the roots and the shoots in the xylem and phloem.
• Storage of nutrients. • The production of new living tissue. The
normal life span of plant cells is one to three years. Stems have cells called meristems that annually generate new living tissue.
• xylem is one of the two types of transport tissue, phloem being the other
Types of stems Herbaceus stems• Annual plants: plant with a year life-time.
Weeds generally belong to this group.• Vivacious plants: plants with aerial stems
lasting a single season, but keeping underground structures from wich new stems spring again next season.
Ligneous stems• Trees: in this case we call the stems
trunks.• Shrubs: they grow from one to five meters
tall and their branching begins at soil level• Bushes: they grow shorter than one meter
tall.