Author Stephen King is thumbing his nose at the publishing industry. On Monday he will begin an experiment in which he will post the first installment of his new novel, “The Plant,” on his Web site and then he will ask readers to send him a check or money order for one dollar. (Parts II will appear Aug. 21, and if sales are good, III will be posted in September.) Payment for the 5,000-7,000-word installments is strictly on the honor system. “If you pay, the story rolls. If you don’t, the story folds,” King, 52, states on his site. “My friends, we have a chance to become Big Publishing’s worst nightmare,” he writes of the experiment to “break some trail for all the midlist writers, literary writers, and just plain marginalized writers who see a future outside the mainstream.” Later he adds, “I love my editors, and I like my publisher.” King’s first e-book, “Riding the Bullet,” became downloadable on the Web last March. The plotline of “The Plant”? “The story is sort of funny and at the same time pretty gruesome,” he writes.