Roots absorb ions (and small amounts of some small molecules non-specifically) through protein channels. The largest channels are about the diameter of a small anionic dye ion. Most channels are specific for a particular nutrient ion or water. Outdoor soils contain essential oils, you can smell them when cultivating moist organic soils. I don't think roots absorb very much e/o.
E/o, resins and alkaloids are the most common medicinal compounds found in medicinal plants. Used in pharmaceutical preps for 1000s of years. Shortages of thymol in WW2 forced them to use less effective carvacol for wound dressing. Still used extensively today, many e/o's are now produced in chemical factories. New uses like Rosemary extract (rosemarinol) to preserve meat.
E/o's (mono, sequi and a few di-terpenes) and resins (mostly di-terpenes) are very important for cannabis medicinal effects. E/o is readily absorbed by the lungs, moves through most tissues easily, across the blood brain barrier a few minutes later.
Add e/o to bud? I guess a small amount of e/o might cross the cuticle to enter into solution in the globular head.
Why bother adding e/o. Breeders should make varieties with high e/o content, not stealth varieties. Growers gotta learn their trade to make bud with high e/o.
Cannabinoids alone have medicinal value and you get a little high. Mixed with the right blend of e/o and resin, potential for much more medicinal value. And you can get very high.
I wonder about some LP's, almost no e/o, like they don't want people to get high.
