" The stages of yoga are eight : Yama (moral commandments), Niyama (rules of self-purification), Asana (yoga positions), Pranayama (control of breathing), Pratyahara (withdrawal of sense), Dharana(concentration), Dhyana (meditation) and Samadhi (absolute bliss,salvation). They are all integrated.
A tree has roots, trunk, branches, leaves, bark, sap,flowers and fruits. Each one of these components has a separate identity, but each component can not by itself become a tree. It is the same with Yoga. As all the parts put together become a tree, so all the eight stages put together form Yoga. The universal principles of Yama are the roots and the individual disciplines of Niyama form the trunk. Asanas are like various branches spreading in different directions. Pranayama, which aerates the body with energy, is like the leaves which aerate the entire tree. Pratyahara prevents the energy of the senses flowing outwards, just as the bark protects a tree from decay. Dharana is the sap of the tree that holds the body and intellect firm. Dhyana is the flower ripening into the fruit of Samadhi. Even is the fruit is the highest development of the tree, the realisation of one’s true self (atmadarsana) is the culmination of practice of Yoga." (Iyengar)