One goes up... and one goes down. I was a college freshman in Botany 101 when I first learned about xylem and phloem, the two transport tissues which carry water and nutrients up and down a tree's trunk. The two fluids, I learned, work in tandem:

Xylem [zī' ləm] effectively sucks water and minerals from the earth, drawing nourishment into the roots, then upward along a tree's trunk or a plant's tender stem, into the aerial parts of the plant – the leaves and flowers and fruit. Some of that water is released into the air in a process called “transpiration,” helping smaller insects like moths to maintain a steady body temperature. Excess moisture is drawn upward by the heat of the sun, becoming clouds and then eventually dropping as rain on the earth below.

But that's not the whole of it. Located in the leaves are chloroplasts, tiny energy factories which collect energy from the sun, then convert carbon dioxide and water into sugars through the process of photosynthesis. Then the plant, exuberant with liquid nourishment, sends those sugars as Phloem [flō' əm] back down the plant's arterial system, carrying food and nutrients downward to storage areas (such as roots and rhizomes) and to the new growth areas.

It's pretty neat, the way it all works together! The whole system reminds me of... well, of God! The complex ecosystem that ensures that the plants on which we depend will be healthy and strong is mirrored in our relationship with our Creator. One might think of prayer as the xylem, and grace as the phloem.

When we pray, our thoughts and our worship and our deepest earnings travel up, up like the water and minerals in xylem, from way down here on earth to God, Who rules the heavens and the earth. God, for his part, sends down his grace – like phloem, pouring down to fill our hearts and minds, strengthening us to know his will and to act accordingly. God's grace is always available to us; but when we pray, that transformation is accelerated as God answers our prayer, opening the heavenly gates to offer more, still more of his abundant graces. Like phloem, God's grace makes its way to where it is needed the most – our hardened hearts, our confused minds, our timid wills. Like phloem, grace stimulates the “new growth areas,” spurring us on toward virtue and filling us with love and with a resolve to do his will.

Who wouldn't want that?