Aldiss has already affectionately plundered the space-opera inventory in an anthology of that name (1975), followed by Space Odysseys (1976) and now by a two volume installment. Here indeed is a vegetable love to grow vaster than the Oxford English Dictionary--Aldiss keeps coming up with selections of real merit and/or historical interest. These volumes are equally strong; most of the 26 stories date from the Forties and Fifties. They include such nuggets as the original short-story version of Asimov's Foundation (rather callow and unfleshed, truth to tell) and a bit of incisive iron-gray suspense--involving hot pursuit across parallel space-time probabilities--by none other than John D. MacDonald. Space-opera fans will slurp up the cardboard thrills of Gardner Fox's ""Tonight the Stars Revolt!"" and Alfred Coppel's ""The Rebel of Valkyr."" On another plane, there is a splendid A. E. van Vogt about a ship's captain interrogating a mysterious interstellar weather-watcher, a gentle Clifford Simak about a human immigrant learning to make the most of a frustrating alien utopia, and one of James White's nimbler medical-detection chronicles of Sector General, more formally known as Galactic Sector General Twelve Hospital. R.A. Lafferty re-examines the monkeys-and-typewriter situation with mad inventiveness, and there are excellent stories by James Blish, Cordwainer Smith, and Poul Anderson. Aldiss' notes and introduction are a disappointment, full of scattershot generalizations and hello-fellow-kitsch-lovers jocularities that are far from the best capabilities of this fine sci-fi writer and critic.