Wednesday, March 18, 2015
Fragrant Foliage
If you’ve ever brushed against a scented-leaved Pelargonium like the one above (or any other fragrant-leaved plant) and noticed the scent, here’s where that fragrance is actually stored. The leaves are covered in fine pointed hairs (second photo from bottom) but scattered amongst them there are two other kinds of hair – short (third from bottom) and tall (fourth photo from bottom). At higher magnification (top photo) you can see the oily fragrance compounds stored in the bulbous cell at the tip of the hairs, that are released when the hairs are damaged. These fragrance chemicals are a key part of the plant’s defence system against insects and are secretions that either make the leaf too sticky for small insects to move around or repel them, but commercially they are of immense importance in the fragrance industry. Many of those scents that saturate the air around the perfume counter in department stores contained chemical compounds distilled from the ‘gunk’ that you can see in these plant hair tips. Perhaps the most extraordinary is labdanum, which is stored in the sticky hairs of Cretan rock roses (Cistus species). Tradionally, this was once collected by scraping it off the fur of goats that grazed amongst the Cistus shrubs on Cretan hillsides. You can read about it at http://botano.gr/herbs-and-spices/cistus-creticus-labdanum.html
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