Nitrogen fixing root nodules - ever wondered what they look like?

I have often wondered about this ... all gardeners learn about the joys of legumes, that class of plants which are particularly useful to gardeners, because they possess the useful ability to "fix" nitrogen, ie to take it in from the atmosphere, convert it into something useful, then put it back into the soil so the plants can benefit from it.

We like this, because nitrogen is a fertiliser, and we spend much of our lives adding it to our gardens, in the form of soil conditioner, organic matter, liquid feeds, and chemicals such as Gro-more, 

The "usual suspects" in the legume family are things like broad beans, and runner beans in the vegetable garden: and the clovers, which are sometimes used as green manures. 

If you look up "nitrogen fixing nodules" on the internet, you get pictures of things like this:

This, apparently, shows the nodules on the roots of Medicago, a common weed wildflower.

There's no indication of scale, here, but I know that Black Medick is a small weed, and the roots are quite tiny, so these must be pretty microscopic.

So I have grown up with the idea that nitrogen fixing nodules are teeny, tiny things, not easily visible to the naked eye.

Then, last week, I was moving some mature Lupins, and was very surprised to find a whole lot of lumpy things on their roots:

Here we are - right - with my Trainee's hands for scale.

Can you see all those lumpy things on the roots?

At first, we wondered if they were galls of some kind: I have never seen anything like this, before.

Here's the best I can manage for a close-up - left - as my phone isn't very good at getting up close and personal to plants and things.

See how huge they are?

Great roundish knobbly things... whatever can they be?

Well, apparently, these are indeed nitrogen fixing nodules, according to my friend and colleague, Robert (*waves*), who tells me that on lupins, they can indeed grow quite large.  

Large enough to be seen, very clearly, with the naked eye.

So there you go - now we have all seen some actual nitrogen-fixing nodules!

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