Thursday, September 08, 2022

Designing A Plant Growth Experiment

A while back, when I posted an update to my tobacco plant growth, Tim left a typically interesting comment, wondering about plant growth in general.  I replied saying that I think plants grow as a percentage of their size, a kind of vegetable compound interest.

How could you quantify this?

Oregano is a ground-hugger and it grows like the weed that it is. What if you cleared out some space, outlined the area in a circle and planted the oregano in the center. A photo from above would allow you to measure the percent of the circle inhabited by oregano. That ought to give a decent measure of growth.

If you did an experiment with tobacco, you could measure height, but that doesn't seem to get the volume of the plant. Since oregano clings to the Earth, it's more of a 2-dimensional creature and better suited to photo measurements.

Kind of like this.

It's something to ponder.


tim eisele said...

Yeah, that's usually the problem in designing biological experiments - how do you quantify the results?

You might actually be able to use image analysis to estimate the leaf area and volume of plant matter. For the tobacco plants, given that they have a generally conical shape you might get a reasonable proxy for the actual mass of plant matter just from measuring height and leaf-span when measured from the side, and calculating the volume of the smallest cone that would fit over it. And then estimate the active leaf area by holding your camera at the angle the sun would strike the plant, and measuring how much green area there was in the picture.

Ohioan@Heart said...

As I recall (from the dim recesses of mind), plants are typically modeled as having a non-Euclidian (i.e., fractal dimension), which tend to run between 2 and 3. Anyways, I’d expect the dimensionally of the growth to reflect the same. Your oregano should be less than the tobacco, but that’s as close as can come. Mandelbrot goes on for pages about this (and it is persuasive, at least to me, but he really never does anything in the way of actually trying to measure it for a real plant).