I’ve looked at sap a few times, mostly to see what ions it carries, not to wire a circuit. Most sap is just water with a smattering of potassium and sodium, so its conductivity is modest—like a very diluted electrolyte. A few species, like the rubber tree or certain conifers, have higher ion loads, but the voltage you can extract is tiny, more useful for bio‑fuel cells than for building a whole circuit. I’m fascinated by the medicinal plants with high alkaloid content, but using them as power sources? That’s a curious idea—just remember that the same compounds that heal can also corrode metal, so a gentle, controlled environment is essential.