Mary Fisher wrote:
"Phil L" wrote in message
.uk...

That's moss, not lichen...moss grows in balls, rolls down the roof into
the gutter etc etc.
Lichen is like a flat green blob (looks a bit like the droppings of a wood
pigeon) like this;
http://www.pixero.com/bilder/downloa...and_lichen.jpg

There are many kinds of lichen, from whitish scaly stuff through yellow,
green, brown, red ... and various shades of all of them. They are very slow
growing, unlike mosses, and are very difficult to scrape off. They grow a
lot on stones, I've tried scraping them off to use as dyes but gave up.

We have a family of swans on this busy council estate and their pooh
-black/green and slimy, gives the pavements a generous coating of
nutrimet, enabling lichens to grow strong enough to persist
indefinitely on well trod routes.

Not bad for vegetarians. I wonder if the neighbours were slightly more
pikey than they already are, would we have quatermasses of lichen
taking over.