system
Given the following post, respond as if you're commenting on Reddit:
human
Does my Christmas tree really drink from its stump or am I just kidding myself when I water it?

And if it does drink, how is it able to do so without its roots? Can the trunk just absorb water at any level of the tree?
gpt
You have to remember that plants rely on the physical properties of water to move it around.  Trees and other plants have no "beating hearts" to artificially move fluid around, so they rely on osmosis.  As water evaporates from leaves (or in your Christmas tree's case, needles) it sets up an osmotic imbalance in the tree, where the concentration of water at the "stump" (which is soaked in water) is greater than at the tips of the brances, where water is evaporating more rapidly due to the higher surface area and much higher permiability of the leaves/needles (higher compared to the trunk, that is).  The xylem and phloem of the tree are still intact inside the trunk, so the water naturally moves from the area of high concentration to the area of low concentration, along the same channels a full rooted tree would use.  Incidentally, this is why coniferous trees with waxy needles are more drought resistant than deciduous, leafed trees.  They lose water less rapidly from waxy needles than deciduous trees do from delicate leaves.

The main thing roots do is create areas of higher surface area in the soil, allowing the tree to absorb more water in dry conditions.  Roots are just the absorbing conterparts to the respirating leaves.  Roots also do a few cool things like exude acids into the soil to facilitate the absorption of important chemicals like phosphorous, nitrogen and magnesium, but at their simplest, they're just parts of the tree designed to put the most surface area possible in contact with the relativly wet (compared to the air) soil.  But basically, if the truck is litterally sitting in a pool of water, they're not really that necessary to just move water up the tree.  Now, the tree couldn't survive forever like that, unless you were adding the right fertalizer mix to the water to make sure the tree was getting all the nutrients it needed, but for a few weeks in December, the tree is just fine "drinking" from the stump.

TL:DR:  Yes, your tree drinks through the stump!