Farmers' markets are one way for city dwellers to mark the seasons: fall begins when the Gravenstein apples appear; winter must be survived on broccoli and root vegetables; and then the first asparagus shows up, cluing us in that spring is indeed on the way. With the first glorious peaches and nectarines, summer has officially begun. The Old Oakland farmers' market, held on Fridays from 8 a.m. to 2 p.m., well befits a city that prides itself on cultural and ethnic diversity. Its two blocks are almost impossibly crammed with vendors, and the streets are packed with shoppers elbowing and pushing their way toward a favorite farmer. A security guard at the corner of Washington and Ninth tries in vain to stem the tide of humanity determined to cross against the stoplight. The real draw here is exotic produce. The market is just across Broadway from Chinatown, and fruits and vegetables on offer include bitter melons, long beans, pea greens, huge bunches of coriander, and lemongrass. One stand has big bins of evil-looking tiny red chiles -- with yellow ones nearby that look even more menacing. Eggplants range from big dark globes to long skinny paler purple ones to tiny striped Ping Pong ball-sized ones. Want a hot date? One vendor has deglet noor, bread dates, and "ripening like banana dates," which, a sign declares, "get sweeter and softer every day."