Auxin: A plant hormone that simulates elongation of young developing shoots.  The type of auxin found naturally in plants is the compound indoleacetic acid (IAA).  Primary production of Auxin is in the apical meristem - the tips of roots and stems.  Auxins are responsible for phototropism, the growth pattern of plants toward sunlight (flash animation below).  Auxins promote growth on the "dark" side of the plant so that the stem bends toward the sunlight.  And are also involved in cell elongation and fruit development.

Gibberellins stimulate cell elongation - aka growth. These are also often tell the plant embryo to cease being dormant and germinate.

Cytokinins are forms of adenine that promote cell division and differentiation through the stimulation of molecular syntheses in the cell.

Ethylene is a gas product of plants that causes the termination of leaf growth and promotion of fruit ripening.

Abscisic acid (ABA) is a hormone that inhibits leaf abscission (termination of leaf growth) and causes buds and seeds to become inactive. Another example of ABA is the closing of stomata when leaves begin to wilt due to loss of moisture.

Next:  "Animal Endocrine System."