The transport of water

Water

Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

 and nutrient

Nutrient

A nutrient is a chemical that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. They are used to build and repair tissues, regulate body processes and are converted to and used as energy...

s through the voluminous cortex of the cactus

Cactus

A cactus is a member of the plant family Cactaceae. Their distinctive appearance is a result of adaptations to conserve water in dry and/or hot environments. In most species, the stem has evolved to become photosynthetic and succulent, while the leaves have evolved into spines...

 is possible because of the presence of a vascular system exclusive to cacti, the cortical bundle. The cortical bundle emerges radially from the xylem and produces shoots that run tangentially to the cortex, branching extensively and vascularizing every part of the cortex.

Because cacti live a long time, the cortical bundles have to function for many years. In every cactus species, the cortical bundles produce secondary phloem

Phloem

In vascular plants, phloem is the living tissue that carries organic nutrients , in particular, glucose, a sugar, to all parts of the plant where needed. In trees, the phloem is the innermost layer of the bark, hence the name, derived from the Greek word "bark"...

s. In very old cortical bundles located at the base of very old shoots, the secondary phloem may attain a thickness of several millimeters.

External links

• http://www.cactus-art.biz/note-book/Dictionary/Dictionary_C/dictionary_cortex.htm
• http://aob.oxfordjournals.org/content/70/4/317.abstract
• http://www.sbs.utexas.edu/mauseth/weblab/webchap11stem/11.3-7.htm