In today's excerpt--the definition of spice:
"Broadly, a spice is not an herb, understood to mean the aromatic, herbaceous, green parts of plants. Herbs are leafy, whereas spices are obtained from other parts of the plant: bark, root, flower bud, gums and resins, seed, fruit, or stigma. Herbs tend to grow in temperate climates, spices in the tropics. Historically, the implication was that a spice was far less readily obtainable than an herb--and far more expensive.
"...Chemically, the qualities that make a spice a spice are its rare essential oils and oleoresins, highly volatile compounds that impart to spices their flavor, aroma, and preservative properties. Botanists classify these chemicals as secondary compounds, so called because they are secondary to the plant's metabolism, which is to say they play no role in photosynthesis or the uptake of nutrients. But secondary does not mean irrelevant. It is generally accepted that their raison d'etre is a form of evolutionary response, the plant's means of countering threats from parasites, bacteria, fungi, or pathogens native to the plant's tropical environment. Briefly, the chemistry of spices--what in the final analysis makes a spice a spice--is, in evolutionary terms, what quills are to the porcupine or the shell to the tortoise. In its natural state cinnamon is an elegant form of armor; the seductive aroma of nutmeg is, to certain insects, a bundle of toxins. The elemental irony of their history is that the attractiveness of spices is (from the plant's perspective) a form of Darwinian backfiring. What makes a spice so appealing to humans is, to other members of the animal kingdom, repulsive.
"By any measure the most exceptional of the spices, and far and away the most historically significant, is pepper. The spice is the fruit of Piper nigrum, a perennial climbing climbing vine native to India's Malabar Coast...Black pepper, the most popular variety, is picked while unripe...White pepper is the same fruit left longer on the vine."
Jack Turner, Spice, The History of a Temptation, Vintage, 2005, xix-xxi.