Last weekend, I was busy working with student papers, so today I have two experiments to report, from this week and the week before. On the week before, I ran a straight-up repetition. As described two weeks ago, the very first experiment with roots on plates ran suspiciously well. Before launching real experiments, I want to make sure things really are as smooth as they seem. For the repetition, I made sure to protect the plants from light from the computer screen by opening the laptop, launching the time-lapse acquisition program, and then closing the laptop all before opening the box containing the plants. But otherwise, a simple repetition. And the results were simply repetitive (compare circles and squares in Fig. 1).

The figure plots the growth rate of the roots versus time. The curve with squares and the one with circles both go up steadily over the 11 hours or so of measurement, meaning that the roots grew steadily faster. To be sure, all the rates for the squares were a bit higher than the circles. I don’t know why. The curves bounce around a little but this is reasonable because there were only five individual seedlings per experiment.

In principle, it would be convenient to have a growth rate that was more steady over time. I wondered whether the roots were growing slowly at the start of the experiment because they were only a little more than one centimeter long when I put them on the plate. This is pretty short. The roots might need a bit more time to ramp up and reach a stable growth rate. In the literature, maize roots given constant conditions are often reported to grow at a steady rate. I decided try starting the experiment with roots that were one day older than used for these experiments. But because the roots grow rather far in 24 hours, to minimize the chances of having too long roots, I trimmed the total growth time a little by starting the seeds in the late afternoon and setting up the experiment in the morning. For the circle and square experiment, I had soaked seeds in the morning and set up the experiment in the late afternoon.

On that morning when I unrolled the jelly roll to start the experiment, I was puzzled to find short roots. Indeed, roots were about the same length as what I would have expected to see the day before. The shoots were big, ruling out some global poison. I set up the experiment anyway and it gave a similar time course (Fig. 1, triangles), although in this case the growth rates were even higher than the squares.

But the short stature of the roots indicates a problem. I suspect toxic towels! When I explained a few weeks ago about making jelly rolls to germinate the maize seeds, I described sandwiching seeds between brown paper towels to keep the roots from disappearing into the spongy germination paper. But in setting up the jelly roll for the circle experiment (i.e., the first one) I noticed towels in the lab, white ones, that were narrower than the brown ones; using these narrow towels would save me the trouble of cutting the brown ones down. All three experiments in the figure were done with seeds germinated in white-towel jelly rolls. The towels might be laced with some kind of glue that is inimical to maize roots and the initial period of slow and increasing growth reflects recovery. Alternatively, deep in the jelly roll, conditions might go anoxic. I don’t recall this kind of problem before with brown-paper-towel jelly rolls but maybe I wrapped them tighter lately?

Anyway, on Friday, I set up two jelly rolls, one with brown paper towels and the other with white. I also placed some seeds on germination paper at the bottom of the box, no jelly roll whatever. On Monday I will compare them and if the brown paper towel crew is suitable then I will image a set on a plate.