LEAF EVOLUTION : SOURCES : ALCHEMY
The alchemists sought to transform one element into another - something accomplished by leaves within their cell structure every moment of daylight, thus making life on earth possible. It's recognised now that what the alchemists were trying to do was in fact to speed up evolution - although they had no knowledge of the term, but believed life to be a continuum from the mineral, base metal to more refined metal, to vegetable, to animal. So they hoped to persuade lead to evolve into gold, and thence into "vegetable gold", the "philosopher's stone" and the elixir of life - the basic substance of life, which we might call "the life force" today.

The four elements, earth, water, air, fire, corresponded to the four humours (subtle essences) and four temperaments of human beings. People were classified as predominantly one temperament or another, according to the balance of humours in their body. Ill health could be healed by re-balancing the humours. Modern endocrinal medicine is returning to a similar holistic view of the body, with its functions balanced by various hormones and other subtle fluids.

Each humour was thought to partake of a combination of four qualities, hot, dry, moist, cold. This philosophy was at the basis of both medicine and alchemy, there being less division between the sciences in earlier times.

The temperaments corresponded thus:
Phlegmatic - earth - cold and dry
Melancholic - water - cold and moist
Sanguine - air - warm and moist
Choleric - fire - hot and dry

The names of the temperaments have survived as descriptions of personality types or moods which most people would recognise.