As recently as twenty years ago the isolation of natural substances and the elucidation of their structure had to be performed almost exclusively by chemical means. Large quantities of starting material were required, and time consuming methods had to be applied. As a result, only the main constituents of essential oils were discovered. Thus, progress in this field was very slow.
The discovery of gas chromatography by James and Martin and the development of spectroscopic methods revolutionized the analysis of natural products. Suddenly it became possible to detect trace components. (By trace components I mean sensorily active compounds which are present in a complex mixture in amounts below 1%. This level is obviously chosen arbitrarily.)
This revolutionary development is particularly impressive in the field of flavors, if the number of products discovered in one year is taken as a measure. In 1967 not more than 750 aroma components were known, but today there are around 3,000. This means a quadruplication within the last 10 years. We observe the same tendency in the field of essential oils, and there is no sign when this curve is going to level off.