This boxed set is a project worthy of the Franklin Mint. It spreads sixty-five tracks across three CDs, three tapes or five LPs, which are packaged in a nice purple box with a twenty-four-page booklet.

Although subtitled The Definitive Collection, the album is filled with four hours of largely unreleased flotsam and jetsam that plays to the sensibilities of the collector, not the casual listener. Noted iconoclast Ian Anderson — Jethro Tull's flute-playing main man and madman — left no stone unturned and avoided obvious choices. He's collected twenty-three live cuts, nineteen studio outtakes and twenty-three previously issued recordings, fifteen of them rare B sides and whatnot. Of the meager eight tracks that appear as they did on Jethro Tull albums, Anderson's choices verge on the eccentric: "Cheap Day Return," from Aqualung, and "Only Solitaire," from Warchild, for example.

The encyclopedic set is subdivided into "The Radio Archives," "Rare Tracks (Released but Only Just)," "Flawed Gems (Dusted Down)," "The Other Sides of Tull" and "The Essential Tull." The radio material — especially the BBC shows from 1968 and '69 — is the most interesting. You can hear the nascent band catapulting into the unknown as it hybridizes blues, jazz and progressive rock in fresh ways.

For their own part, the rare tracks are not shoddy outtakes but rather songs that didn't fit into a given project. Because Tull has often been conceptually heavy-handed, these leftovers sometimes prove more listenable than the leaden albums they failed to make.

The "flawed gems" and "other sides" are the real litmus test of devotion to this band. You can hear the hinges creak on some of these riff-sodden songs; others are promising experiments. Of the latter, a three-song suite from a scrapped 1972 album, here dubbed "The Chateau D'Isaster Tapes," is more dynamic than its title might suggest.

Obviously, "The Essential Tull" is something of a misnomer, since only one Tull standard, "Bungle in the Jungle," appears as it did in its original release. Still, the live versions of such Tull classics as "Aqualung" and "Locomotive Breath" — numbers for which nearly every arena goer in America has flicked his or her Bic at one time or another — are performed in sprightly, spruced-up versions that belie their age.

By weight and volume, 20 Years of Jethro Tull is cumbersome. Yet in reconstructing the history of his band, Ian Anderson has emphasized its lilting, acoustic-textured aspects and removed ballast from heavier Tull favorites in the more limber live arrangements he chose. With its obsessive emphasis on unissued material, this boxed set is perhaps best described as a deluxe souvenir for serious fans only. Yet there are doubtlessly some recent Tull converts who will dive into this deep mother lode headfirst — and not come up disappointed.

“Help Me”

Joni Mitchell wrote and recorded this song for her album Court and Spark, but she had to switch from her regular band to make the song sound exactly the way she wanted. "I had attempted to play my music with rock & roll players," she told Rolling Stone. "They’d laugh, 'Awww, isn't that cute? She's trying to teach us how to play.'" Mitchell switched to a jazz band, Tom Scott’s L.A. Express, and scored the biggest hit of her career in the process.