A Literary Form Without A Name
The novel that comprises a number of seemingly independent stories -- usually of novelette or novella length -- appeared only with the advent of literary Modernism (the earliest example I can think of is Hemingway's "In Our Time," and that only if you don't declare it a collection), and has never been terribly popular, in large part because it seems to confuse publishers. (Random House insisted in calling Faulkner's novel "God Down, Moses and Other Stories" in its first edition.) But it is a form that affords great pleasures.
It is also a form that is particularly common in science fiction. John Clute once coined the term "fix-up," which he has since decided causes more problems than it solves, to describe novels that first appeared in independent sections in magazines. Early examples include A.E. van Vogt's early work, as well as Asimov's "Foundation" novels. The problem with "fix-up" is that the term can be used to describe a straightforward story series eventually published in volume form and called, perhaps for obvious commercial reasons, a "novel" rather than a "collection." Van Vogt's "The Voyage of the Space Beagle" is a fix-up by this definition, but it isn't at all a single, unified work. So "fix-up" doesn't help us, either.
Perhaps the first really good example in SF is James Blish's "The Seedling Stars" in 1957. The novel's five sections share no characters or locale, and each is set in a widely differing era. The volume is a unified novel, however, held together by forces other than the usual narrative continuities. You don't find too many artistically fruitful examples over the next dozen or so years, although some prolific writers -- Robert Silverberg, for one -- would bat out stories set in a single milieu until he had about a volume's worth and then published them as a novel. The only one I can think of that really made use of the form's peculiar resources is Keith Roberts's "Pavane" (1968).
The early seventies, however, saw a bunch of them. The Wolfe and Disch novels I cited, plus Disch's unfinished "The Pressure of Time," Roberts's "The Chalk Giants," and, I suppose, Asimov's "The Gods Themselves." This minor trend continued through the decade -- I remember examples by Joe Haldeman, Kate Wilhelm, Richard Lupoff, Pamela Sargent, plus one that Harlan Ellison never finished -- then seemed to trail off.