Difference between VOLATILE OIL&FIXED OIL?

Essential oils(volatile oils)are steam volatile while fixed oils on heating ,decompose and therefore can not be distilled.Fixed oils form a permanent stain when a drop is placed on paper or cloth while volatile oils(essential oils) do not form a permanent stain because they evaporate.Essential oils (volatile oils) are derived from mevalonic acid and shikimic acid while fixed oils are derivatives of polyacetic acid and are glycerides of fatty acids The principal source of fixed oils is the seeds of plants while volatile oils are present in barks,leaves,roots,in petals