Did you do this in grade school? You should do it again. Watching beans grow inside a jar is like Jack and the Beanstalk meets x-ray vision.
I did it recently to get pictures for a Gardening with Children Master Gardener presentation I was writing. But with the beans growing right beside me on my desk, I could not stop obsessing over roots and shoots and roots again! And so began my geeky, grownup fascination with the bean seed experiment.
Seeds from last year’s scarlet runner beans (Phaseolus coccineus) were the subjects. The stage was an old lab jar lined with moist paper towels, with a crumpled paper towel in the bottom to wick up moisture.
The seeds went in, some upside-down and some sideways, between the paper towel and glass roughly half way down the jar. In hindsight, they could’ve been higher to make room for the roots, but half way held these large beans in place.
Have you ever paid close attention to a bean seed? I mean, it’s a bean, after all. What could be simpler? A balloon-like oval with a belly button. Well, after countless beans planted over a lifetime, my eyes have been freshly opened.
Confess. Have you paid much attention to that itty-bitty, pimple-like bump, called the hydropyle? I hadn’t. Right there beside the “bellybutton” (or hilum), which marks were the bean was attached to the pod, it’s more important than its insignificant appearance suggests. At fertilization, the hydropyle is where pollen would have entered the ovary. At germination, aka when the bean sprouts, it’s where water enters the seed to trigger the growth process.
All of this piqued my need to find out as I noticed where the roots always appeared first. That tiny hole must also make a convenient break in the tough bean skin, perfect for the tiny emerging root to escape.
The idea that a plant’s roots respond to gravity was introduced to me in Daniel Chamovitz’s excellent book What a Plant Knows. Find it. Read it. It’s short (less than 140 pages), science-y, and full of wonderful, easy-to-understand info. This article from NPR.org gives the nutshell details of gravitropism in roots.
Yes, lots of good Scrabble and crossword words in this post.
Once the bean gets going, things move along quickly. About 10 days after the first questing roots appear, growth has advanced significantly, up and down.
The most fascinating aspect for me was the part we don’t usually see: the roots. The root caps that act as armour allowing tiny roots to drill through the soil were highly visible. Behind the caps are the areas of active cell division (meristematic cells) that cause the roots to elongate. Also near the tips are the weighty cells you saw in that link earlier that respond to gravitational forces and sending the roots downward.
If you look closely, you can also see a little fungal growth happening in one dark area. I also wondered if the round blob on the left near the top of the tap root might have been a root node created to fix nitrogen. Members of the legume family, such as beans and peas, do this in collaboration with soil microbes. But on further research into the nitrogen-fixing process (recommended reading for soil and plant fanatics like me), I concluded: it’s just a round blob.
Cursor over the smaller images to read the captions, or click any image for a slide show (unfortunately, without captions).
My little friends lived beside me in my office for the better part of a month. I became very attached. As you’ve strolled through this with me, rather than thinking I have too much time on my hands, I hope you’ve thought of it as taking a few minutes for horticultural mindfulness over the course of three weeks or so.
At a certain point, however, I knew it would be time for us to part. As beans don’t transplant well once the roots develop (though you can pre-sprout them to speed up germination before planting) and as it was February – and February 2019 in Toronto – they had to meet their end in the compost. Thank you, little beans, for educating me so well!
If you want to try the bean seed experiment, or try it again, this activity sheet from Kean University in New Jersey is a terrific primer. Let me know if you do.