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If you spend a little time gardening, you soon become aware that plants store energy in their roots, which they collect from the Sun through their leaves. By the end of Autumn, perennials usually have thick roots—the best time for making them into tinctures. In the Spring, many perennials produce new stalks, flowers, and leaves in a burst of growth which depletes their roots, leaving them shriveled up and needing a summer to replenish. Biennials produce no flower or seed their first year. Instead they produce only leaves to gather sunlight to store energy in their roots, which they expend in their second year to flower and reproduce. Some annuals, like potatoes, store up energy in tubers underground, which then power the growth of new stalks and leaves—or supply energy for us when we eat them. There are yet more variations, but you get the idea: plant life is a yearly rhythm of collecting energy, storing it, and using that energy to fuel the start of the next cycle.

I figure the ancients and medievals spent a lot of time gardening or doing its larger-scale variant, agriculture, so all of the above must have been even more obvious to them. How, then, did they describe the yearly flow of energy from Sun to leaves to roots to new plants? What did they call the thing that the plants accumulate and store in their roots? Or did they not think of it this way at all?

diagram showing light energy entering through leaves and being stored in fruits or tubers

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    "Or did they not think of it this way at all?" I think this, but if there is anything in it, it might be found in Vergil's Georgics or Columella. I don't remember reading anything similar at all in Catos' De Agri Cultura.
    – cmw
    Mar 31 at 4:21
  • @C.M.Weimer: Or perhaps (natural) philosophers like Epicurus, Lucretius, Aristotle? I could imagine terms like vita, vitalitas, medulla, dunamis or similar being used by some philosopher. P.S. Lovely question. P.P.S. Or perhaps simply sucus "juice", which was also used metaphorically for "strength".
    – Cerberus
    Mar 31 at 5:01
  • @Ben Kovitz: This Q. could have been: "Did the Ancients have a Word for Photosynthesis?"; more prosaically, "....Sugar?". OLD gives "saccharon" = "sugar". I thought that the only sweetening agent available to the Romans was honey; perhaps not.
    – tony
    Mar 31 at 8:36
  • @cmw If it's anywhere, it must be in those works, or maybe Lucretius or Aristotle, or even Aquinas. (I've only read short excerpts from each.) I got to thinking about this because seeing everything in terms of flow of (conserved) energy sounds like a distinctively modern scientific way of looking at things (e.g. leaves are "solar collectors"), but how do you miss this in the garden? Without some notion of energy, how do you understand the function of leaves? Or why people and animals get tired after physical exertion? Or why eating food helps with that?
    – Ben Kovitz
    Mar 31 at 11:01
  • Maybe a Latin word for "fuel" was put to use for whatever plants get from the Sun and store in themselves? Indeed when you burn wood, you're releasing it.
    – Ben Kovitz
    Mar 31 at 11:13
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Perhaps the word sucus "juice", which was in any case also used metaphorically used for "vigour, essence":

amisimus, mi Pomponi, omnem non modo sucum ac sanguinem sed etiam colorem et speciem pristinae civitatis. — Cicero, Epistola XVIII ad Atticum, 2.

The Loeb edition translates sucum et sanguinem as "vital essence". I don't have a source yet for this from agricultural or pastoral texts.

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    Interesting: I often say "juice" metaphorically for energy, or whatever is the relevant limiting factor that gets consumed by use (e.g. oxygen), when describing attention.
    – Ben Kovitz
    Mar 31 at 11:11
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    @Cerberus: Winstedt (Letters to Atticus Vol. 2) gives "sap & blood" = "sucum ac sanguinem". In the phloem tubes sugar, manufactured in the leaves (photosynthesis), is transported downwards as a sweet, watery syrup (sap). This, beloved of insects, who gnaw at the tree-bark.
    – tony
    Mar 31 at 12:48
  • @BenKovitz: Exactly! Often used forbattery charge.
    – Cerberus
    Mar 31 at 14:54
  • @tony: Voilà! It makes sense.
    – Cerberus
    Mar 31 at 14:55

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