As harmonica legend and southern gentleman Charlie Musselwhite notes in Todd Kwait's new and fascinating documentary about jug-band music, Chasin' Gus' Ghost, the basic jug band lineup of guitar, harmonica and bass (or in this case, jug), is the very thing that evolved into the electric sound of the Chicago blues. And as any fan of early Elvis, the Rolling Stones, the Grateful Dead, Lovin' Spoonful, Cream, Led Zepplin, Creedance Clearwater Revival and so many other classic rock bands knows, the Chicago blues (and jug-band music) were huge influences in the development of rock 'n' roll.

So there's your lineage right there, and reason enough for all us aficionados of Americana roots music to be interested in the story of jug-band music (hereinafter referred to as JBM).

JBM originally flourished briefly on record in and around Louisville, Ky., and Memphis, Tenn., in the 1920s. Recording and record sales for the music crashed along with the stock-market in 1929 and never recovered until a brief blip during the folk boom of the late 1950s and early '60s. The music and musicians did continue to survive, though, on the streets and in the dancehalls of the region.

Some of the seminal bands included the Memphis Jug Band, Dixieland Jug Blowers, Louisville Jug Band, Mound City Blue Blowers and Whistler & His Jug Band. But perhaps the most well-known champion of the genre was Gus Cannon and his band, Cannon's Jug Stompers. And it's the ghost of Gus Cannon that Kwait trails throughout this 90-minute investigative exploration of JBM's roots. Hence the film's title.

Kwait starts with a trip to see former Lovin' Spoonful front-man John Sebastian in concert with his current "J Band" (J for jug), where he is surprised to discover Sebastian's jug-band roots. From there, the filmmaker traces John's influences back to the folk music boom of the '60s when various white middle-class Americans discovered JBM, this African-American blues genre. For example, Grateful Dead founders Jerry Garcia, Bob Weir and Ron "Pigpen" McKernan started their musical careers in Mother McCree's Uptown Jug Champions, Sebastian was a member of the Even Dozen Jug Band, and Maria Muldaur (of "Midnight at the Oasis" fame) met her future husband, Geoff Muldaur, when the two of them joined up with the Jim Kweskin Jug Band.

Kwait includes interviews with Sebastian, Weir, Kweskin, David Grisman and both Muldaurs, as well as footage of the Even Dozen, Lovin' Spoonful and Kweskin band in full flight. Then he heads off for the Mississippi -- but only after a detour trip to Sweden (no kidding), where he interviews JBM chronicler Bengt Olsson and field recording pioneer Sam Charters to help him along the path.

Back when Charters began his field recording, he recalls in an interview, "it was like the whole African-American community didn't exist." I think he's mistaken, though, when he asserts of black and white America that "we literally knew nothing about each other." Perhaps whites knew nothing of blacks, but I'll bet the reverse was not true. Oppressed groups invariably make it a point to know their oppressors. It's a matter of survival.

In Louisville and Memphis, Kwait gets down to exploring the places where many of the jug-band originators played out their lives. He looks briefly at harmonica great Noah Lewis, mandolinist Yank Rachel and Gus Cannon himself, including a visit to Cannon's gravesite. Blues legend Taj Mahal does an interesting voice-over, recreating some of Cannon's own historical statements. He uses lots of historical footage, audio recordings and photographs where these are available. I particularly liked the current interview material with Charlie Musselwhite.

There follows a moving interlude to mark the premature death by cancer of Kweskin's premiere jug blower Fritz Richmond and to pay homage to his skill with a jug and dedication to the genre. Richmond appears both in concert in the film and in on-camera interviews, including emotional clips from when he knew he was dying.

Kwait concludes his documentary by bringing us full circle, accompanying Sebastian, Kweskin, Geoff Muldaur and others on a trip to the Yokahama Jug Band Festival. Concert excerpts from this event are sprinkled throughout the film. Who knew that JBM was so big in Japan?

My favourite part of the documentary, though, is the footage featuring the Sankofa Strings, a trio of young, contemporary, black singers/musicians who are reviving the roots of African-American string band music (of which JBM is really just one part). The Sankofa Strings (Sule Greg Wilson, Rhiannon Giddens and Dom Flemons) are also taking this music to the next generation of African Americans with workshops in public schools. (Note: This band seems to have evolved since the filming of Chasin' Gus' Ghost into the Carolina Chocolate Drops, with the addition of Justin Robinson and only the occasional continuing participation of Wilson. In whichever incarnation, they are musicians worth paying attention to.)

But whatever band he belongs with, jug and banjo player Don Flemons makes a fascinating point in this documentary about the connection between the percussive rhythmic sound of the blown jug and the percussive mouth music of contemporary hip-hop, which uses the microphone to the same effect as those older musicians achieved with the jug. The similarities are obvious once Flemons points them out. So forget the Rolling Stones. They are just a way stop in a lineage that runs all the way from Gus Cannon (and before) to Kanye West (and beyond).