''I have gathered a garland of other men's flowers,'' the French philosopher Montaigne famously wrote, ''and nothing is mine but the cord that binds them.'' The first decade of the twenty-first century appears to belong to the collagist, for whom the creative act is not creation sui generis, but rather the collecting, cutting and pasting of the already extant. Collage, which began as an art meant to confound the brain with its disparate components, has jumped the flat surface, so that almost all musicians, designers, writers and bloggers might today be described as collage artists. ''Collage Culture'' contains two essays, buttressed by artworks and vividly typeset by Brian Roettinger. The first essay, by Mandy Kahn, chronicles collage's forays into the realms of music, fashion, literature and architecture. The second, by Aaron Rose, examines what he sees as the neutralization of countercultural energies in today's pic 'n' mix world.