Yes I do, Bill. Trees contain a fair amount of carbon dioxide, which is acted upon by temperature. When it's warm, the CO2 expands and creates pressure, which will cause the tree to "bleed" through a wound, or taphole. Colder temps will cause the CO2 to contract, which creates a vacuum and draws water through the roots and up into the crown.
So, the warmer daytime temps expand the CO2 and the resulting pressure increase, (along with gravity), cause the sap to run back down from the crown, creating the flow that sugarmakers harvest. At night when the temps drop, water is pulled back up the tree, replenishing the reservoir. To get a sap run, we need nighttime temps below freezing, (mid 20's), and daytime temps above freezing. (low to mid 40's).
I'll try and post a vid from earlier today, showing the CO2 bubbles in our first run of tubing.
