Fizzy bark

It has been such a wet, dark grey day that I despaired of finding a blip, However, when out walking with Bertie in the late afternoon I came across this tree with patches of froth forming near the base so I thought that I would try snapping that phenomenon. 
When I got home I did a bit of research and found the following explanation: Foam forms on the trunks of trees in heavy rain when the water flows down the bark and picks up dust particles and plant residue. Chemical interactions form a simple soap, generating bubbles which collect at the base of the tree. TRUE or FALSE?