I have a question... lemon balm is allegedly expensive because of the low amount of volatile oils in the leaves. But, if you've ever grown it, you know that it's not a subtle fragrance if you brush up against it. If the oil content is so low, how come it puts off such a strong fragrance?
Matt not that this is really an answer or necessarily complete but the "fragrance" is also associated not only with oil content but also with volatility of the oil. Ex. is bay leaves ( laura nobilis) has probably a higher concentration than Lemon Balm but it's not as volatile so therefor our olfactory receptor sites do not pick up the fragrance due to less of the oil in nose than with Lemon Balm. If Bay has an oil content of 100, volatility of 10, and Balm is oil content of 30, yet volatility of 90 one will "smell"the Balm but not the Bay. Hope that makes sense.