Tuesday, January 15, 2019

My Year of Orchids: Wandering orchid roots

A hundred years ago when I used to teach general biology I tried to spend as much time as I could talking about plants. I can’t tell you how much this was a source of dismay for my students. Especially when I started to talk about the strange habits of plants like thigmotrophy, the way plants grow along surfaces.

Of course I had seen many examples of this working in the field and I had plenty of pictures to share, not that it made anything any clearer or more relevant to my students. Now that I have a little more time on my hands I can observe it in spades with my orchids and I have the opportunity to think about it a little bit more.

Thigmotrophy is especially evident in the way orchid roots function. You may see a large root just growing up or down the bark of a shrub that the orchid is growing on.. Slightly more subtle but extremely interesting to me is when I see a root growing straight down the middle of an orchid leaf. It seems to me that this is a perfect way to pick up water that accumulates in these indentations. Sometimes the root just grows down along, but not attached to its host plant. What are these orchid roots sensing?

Similar to the way roots grow on a leaf they may grow up or down the stem. It’s kind of cool to see that this can happen in any position. Roots don’t have to grow straight down.

On some species I have noticed that when the roots are accidentally pushed sideways they try to correct themselves and face downward. So there must be certain cells in the roots that sense things like surfaces, gravity, and perhaps moisture and they influence the surrounding tissue to grow in a particular direction that’s beneficial for the orchid.

Lots more to think about as I study orchid habits. So curious about the way orchid roots wander in an accidental on purpose manner. 

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