unidentified gall on tree root...

[lipase]

I found these two galls on a root of a tree last autumn. It was difficult to tell which tree the root was from since there were a number of trees in close proximity but my knowledge of tree species is shocking anyway so I wouldn't have been able to identify the tree if i could tell which tree the root belonged to.

Anyway, here's a couple of photos of the galls, I was hoping someone might be able to help me identify it?

[Johnny Redgate]

I think that might be an Alder root nodule. See picture here
File:An alder root nodule gall.JPG - Wikipedia, the free encyclopedia

They are made following invasion by Frankenia bacteria allowing Alder to benefit from nitrogen fixation in much the same way as clover and other legumes do (though with different species of bacteria). Other plants that have a symbiotic relationship with nitrogen fixing bacteria include Gunnera and (if my memory is correct) and the Water Fern Azolla.

John

[The Woodman]

I'd agree with Johnny's ID of a nitrogen nodule, especially if the tree in question was an Alder!