There aren’t a lot of important benchmarks in the intermittent yet persistent genre of pot cinema, but “Pineapple Express” is certainly one of them. It’s like the “Gone with the Wind” of stoner comedies, breezy yet Brobdingnagian, a merry monument to Mary Jane.

Monument is the word, too. I'm not entirely certain there'd be as much burning grass in a six-hour video stream of a prairie fire in Kansas as there is in "Pineapple Express." Even for a stoner comedy, this movie has a serious reefer fixation -- you could probably get half-baked just watching it.

Bakedness of one degree or another is the perpetual demeanor of process server Dale Denton (Seth Rogen), a blue-collar paper pusher who somewhat reluctantly gets his ganja from equally herb-addled dope dealer Saul Silver (James Franco).

They've only known each other for a couple of months, but while Saul feels a borderline "bromosexual" attachment to his client, Dale thinks the fondly fraternal vibes are strictly one-directional. Then Double D inadvertently witnesses a murder perpetrated by a drug lord and a corrupt cop and flees to the first haven he can think of: Saul's apartment.

It's not safe for them to stay put, however, so the boys go on the lam until they can ... well, they aren't really planning that far ahead. Actually, that's part of the movie's charm.

The scenario that develops feels both semi-plausible and completely absurd because so much of it is driven by the bud-blasted decision-making capabilities of our heroes. If they could think straight for two seconds, then they'd probably get high again (which, come to think of it, happens more than once).

Predictably, a lot of the comedy is rooted in simple vulgarity or profanity. And there's an extended and mostly grating subplot involving Dale's teenage girlfriend (hottie-in-waiting Amber Heard, star of the legendarily unreleased splatter flick "All the Boys Love Mandy Lane") that feels like it was forced on writers Rogen and Evan Goldberg and director David Gordon Green by slacker Svengali/producer Judd Apatow.

"Pineapple Express" is pretty obviously pure fantasy, especially in terms of its gunplay, fisticuffs and car chases. The overall failure to depict any negative consequences of cannabis consumption, however, apart from a general fogging of the wits, feels reckless in the extreme.

On the other hand, Franco is a four-star hoot as deadheaded Saul, while Rogen plays the (mostly) straight man with aplomb. A lot of the humor is enjoyably broad, but Rogen and writing partner Goldberg also have a way of adding nuance to even the most obvious jokes.

"You threw up in my printer," Saul says, after Dale is momentarily overcome by panic. A half-second later, you'll think, "Saul has a printer?"

Green, who's best known for his offbeat, intensely emotional, small-scale dramas, shows himself to have a flair for both comedy and action, and deftly soft-pedals the mayhem of the film's high octane finale, which is a lot bloodier than it feels.

Fittingly, for a narco-laffer, "Express" also has good chemistry. What else, really, could make a not-quite-Confucian epiphany like "Bros before hos" not only sound, but actually seem, meaningful?

B

Pineapple Express

Director: David Gordon Green

Cast: Seth Rogen, James Franco, Gary Cole, Danny R. McBride

Running time: 1 hr., 51 min.

Rating: R for pervasive language, drug use, sexual references and violence

Location: Opened Wednesday at theaters everywhere