Friday, February 1, 2019

My Year of Orchids: Root follows water

It’s amazing to me to watch this. The water sticks to orchid roots as a thin coating before it’s absorbed. It’s simple adhesion in action, one of the typical behaviors of water, but it holds so much in the way of biological implications. As epiphytes, living in the air without a direct connection to the soil, orchids are wedded to water in a way few other plants are. They absolutely have to make the most of it.

There’s a lot written about how orchid photosynthetic metabolism utilizes water super effectively. In their own way orchids are like succulents. They open their breathing pores after dark instead of during the day in order to lose less water. This phenomenon is super interesting to me but somehow more interesting is how the orchid body interacts with water. Roots following water is just one example.

You water and watch. A drop of water forms and enlarges at the root tip. This drop lasts longer than the water that stuck to other parts of the root. I don’t know how to describe it except that it’s somehow a “lead” drop, which directs immediate and future root growth. Roots elongate in the direction of water. I’ve seen these drops at the end of thick and thin roots. The root can be suspended in air or it can be running along the surface of its host plant. Mostly the root is growing down with the dominant flow of water. Sometimes it’s growing upward, I presume to reach water flowing from farther up the tree branch. Water seems to direct the way the root will grow.

This all seems simple. Maybe silly. But it taught me something practical. I’ve noticed that orchids I put at branch tips don’t grow as well as those further down. And best is if the orchid was placed in the crook of the of the tree between two branches or twigs. It makes sense doesn’t it? The plant wants to be situated where there’s a bit of extra water. Then the roots can go to work extending in the direction of that extra flow.

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