BBC News, Berlin
Modern Berlin may be a prosperous place but its troubled past has left its mark on the city's character, including a tendency to the alternative. Among the counter-culture railing against society are arsonists, saboteurs, artists and even gardeners.
Petrus Akkordeon, as he calls himself, emerges from the S-Bahn station on to Potsdamer Platz and plants a small flower.
What could be simpler?
Up he comes from the underground into the soulless square, takes out his trowel and digs and gouges between the cracks of the paving stones and plants the shoots - a line of green in the grey of the granite.
Potsdamer Platz today is a long way from what it once was - the pulsating heart of Weimar Berlin, the city's hub of charm and cafe society.
It was where the tram routes met, where the literati met and, no doubt, the not-so-literati. It was the place of chatter and deals and morning-after-the-night-before coffee.
Today, it is, I think, a pretty soulless place.
It was devastated in the war and left desolate after it - split down the middle by the Berlin Wall. On the wasteland freed for development by the Wall's demolition has arisen the cold glass of the Sony Centre, with its windy canyons of offices.
A new sort of desolation, you might think. Until that is, Petrus arrives with his gardening tools.
Petrus Akkordeon, you see, is a guerrilla gardener. He told me he does it to make people happier.
"Everything is grey," he says. "No flowers. No trees. And if you plant one flower, the whole place changes."
"For several seconds, it's a nice place. People see these flowers and feel better for a moment. There's a man planting on Potsdamer Platz, he must be crazy," he says, describing himself, of course.
He may be crazy, but in the nicest possible way. There are worse things to do than disrupt the dreary order of a corporate square by planting a flower.
Yes, indeed. Petrus is at the gentlest end of Berlin's counter-culture, a soul-brother of guerrilla knitters - not people who knit guerrillas but people who knit, in a guerrilla fashion, little cosies for bike stands, or covers for the handrails in the carriages of trains.
At the other end of Berlin's counter-culture, or anarchist culture, are less gentle people.
The police say that in the first half of the year there were 77 politically motivated arson attacks on cars. In other words, about two cars - usually expensive cars - are set on fire each week.
A sabotaged cable caused major disruption to Berlin's S-bahn railway
Banks routinely have their windows smashed in this city. So do upmarket restaurants in gentrified areas.
Back in May, a group sabotaged part of the city's railway system by cutting signalling cables. Nobody was ever caught but someone posted a notice on a website railing against German capitalism.
"Berlin is the capital of one of the leading arms exporters," said the notice. "We struck a blow against this painful and murderous normality. Something has to change. Fundamentally."
So from the violent anarchists to the gentle guerrilla knitters and gardeners, via self-styled artists who live in squats, a "counter-culture" - a minority culture of anger - remains stronger in Berlin than in any other city where I have lived.
At its most benign it is a flower in the granite. At its angriest it is the delays of a severed signalling system on the train network.
There are, I think, many reasons why it remains so strong in Berlin. Firstly, West Berlin attracted radicals because those who settled here were exempted from military service.
It became the base of the Red Army factions whose crazed beliefs transformed an anger at their parents - the so-called Auschwitz Generation - into a violent anger at the post-war West German state.
With much fevered dogma and argument among the intellectuals of the left at the time, the West German state was seen as a continuation of the Nazi state which, moreover, was simply capitalism in its extreme form.
Only in Berlin would people mount a protest under the banner: 'Help! The Tourists are Coming!'
So ran the argument. In the heat of the 1960s, moreover, they also came to see the Americans as occupiers rather than liberators.
You might contend that no city has benefited more from the intervention of American capitalism which, firstly, funded the destruction of the Nazis and, secondly, out-spent Stalin and his successors so the Soviet Union collapsed.
This is not a popular view in Berlin. Even in its post-Hitler, post-Soviet form it remains a less-than-normal city, though perhaps it is getting there.
This a government city, the war having driven industry out. Coming in now are all the moneyed accoutrements of a capital - the accountants and lawyers and, yes, the journalists.
And this brings tensions, particularly to older, down-at-heel areas of East Berlin where many of the attacks on cars and banks and restaurants happen.
The common complaint is that an area like Prenzlauer Berg, where I happen to live, has been inundated by people from - horror-of-horrors - conservative Bavaria, and this is not what Berlin is about. Oh no.
This is not a fully-formed political view. And I do not think anything like a majority view - just a very loud, minority one.
Not everyone welcomes gentrification of areas like Prenzlauer Berg
There are rants, for example, in the fringe magazines about tourists. There are lots of cities where the locals are grumpy about tourists. Londoners get exasperated when foreigners dither on the Tube. New Yorkers grunt when visitors from Wisconsin block the sidewalks.
But only in Berlin would people mount a protest under the banner: "Help! The Tourists are Coming!".
One alternative magazine even urged its readers to "steal their mobile phones and wallets as you walk by their cafe tables, burn their cars, smash their hotel windows, drop rubbish, throw stuff at tourist buses".
The grievances are varied: Tourists rattle their wheelie cases over the cobble-stones early in the morning, they change the nature of nightclubs by taking pictures of each other on mobile phones. The sins are enormous.
Sometimes I call into a small wine shop near where I live. It is run by a man called Peter who has lived here in fast-gentrifying Prenzlauer Berg since he was 13, way before the Wall came down.
I like him a lot and we discuss excellent German wine and moan about how the area has been overrun by yummy mummies pushing baby buggies the size of BMWs, and about how Bob Dylan growl-alikes howl outside the chi-chi cafes to yuppies on their Macs and iPhones.
So much worse than the rather congenial East Berlin way, which is to just get a crate of beer and three or four kitchen chairs and put them on the cobbles outside and drink and talk on the street.
But the two ways squeeze each other. The new trendy bars and the little groups of the old East Berliners on the same stretch of cobbles, jostling for space in Berlin as the city remakes itself.
And in between, I like to imagine Petrus the guerrilla gardener, the sunny side of the counter-culture, planting his shoots in the cracks. Optimistic.
He is bringing colour for all - not just with his blooms, but with a smile as warm as the Berlin sun.
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