On human bodies, the necessary part of us is our brain, at the top of our heads, and if we lose that nothing else matters.
In trees, the root ball where the trunk begins to rise is that part. From there, one could cut away the top and graft something else on and it would make no difference to the tree below, generally.
In humans, our reproductive organs and the exhalation of our waste materials happen below.
In trees, the waste matter goes up, and the flowers bloom on long stalks, where the seeds mature in the air, and spread through the air where our mammalian children run over the land to chase the cottonwood puffs far away from us.
The soul of the plant is in the ground. The way they talk and share knowledge is through the soil where roots spread and form interlocking communities with the complex web of life in the soil. They drink from there, and eat down there. This is where they live their lives, hold their parties, and ease their infants into the world of the living. The roots are larger than the trees above them. Mesquite taproots descend a mile into the earth, down and down like a tower of babel in reverse. Fig roots reach around and spread widely, seeking all the food and water greedy for it.
We are looking at each other, but we do not see each other. We see each other only upside down.
And the trees do see us. The soil is upended, and the bodies descend into the earth. They taste the bacteria and fungi of our skin, the populations of things that live inside of us, and go down into the soil, and from there they communicate with what is left of us, and learn of our strange, above-ground cities.