Bacterial Crown Gall

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 Plant galls are growths or lumps that form on plants as a response to stimulus by other organisms. Insects laying eggs, fungi and bacteria can all cause galls.

I walked past one of my favourite trees in the area yesterday - a wych elm that must be hundreds of  years old- and was struck by the size and number of galls on the trunk of the tree. Here is a close up of some of them.


I reckon that these growths are caused by infection by a bacterium found in soil Agrobacterium radiobacter.  This bacterium infects plant cells and "messes with" the plant DNA causing the plant itself to cause the outgrowth. This life cycle diagram explains it.
The galls don't kill the tree and in some species the burrs they cause  in the timber are valued by craftsmen.

Diary.
I saw three red squirrel at the same time today. The long tailed tits have been at the bird feeders. The new David Attenburgh TV series "Green Planet": aired this week and the new technology used in the time lapse shots is staggeringly beautiful and not to be missed.
I purchase some seed to boost the wildflower meadows a bit. Some of it should not be sown until March but the yellow rattle seeds need to have some frost and "vernalise" so I have been putting some out this week. I have been lazy and have been using the mole hills and using the loose soil as little seed beds all over the field. I will sow the rest of the seed later in the year.






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