Sylvia Plath's short stories deserve to be read and evaluated as pure fiction, and on those terms a few of them will certainly rank high -- the title story in this collection and "Stone Boy With Dolphin," for example, are both masterful explorations of extreme psychological states. But for the present and quite a bit of the future, most of the people who read these fictions will be looking in them for disguised autobiography. They will not be disappointed.

Virtually all of the 20 stories in this collection (which range from masterpieces to unabashed potboilers) contain at least a kernel of autobiography, and also included are five essays (evidently the "prose" of the book's tautological sub-title) and five selections from Plath's copious notebooks, all dedicated to chronicling her day-to-day experiences and observations. In effect, we have here -- fragmentary but richly detailed -- a sampling of what happened in the soul of Sylvia Plath during the decade before her death.

In some instances, the fictional and factual material is dovetailed so that the reader can compare a germinal experience with the story that eventually emerged from it -- or, what is even more revealing, catch a preoccupation in a story and later see it projected into her account of an event in her life. In a 1960 story, "Day of Success," she discusses a young wife's fears that a "brilliant young television producer" may steal her play-wright husband away. The story is one of her potboilers, with a totally unconvincing happy ending tacked on, but it becomes clear how much of herself the author put into it when one reads the notebook entries two years later in which the real-life Sylvia Plath experiences such fears about a neighbor's 16-year-old daughter.

Most of the essays are devoted to memories of childhood which recur thematically in the fiction as they do in some of her poetry. They are largely memories of loneliness, apartness, humiliation, and they blend into fiction about children who suffer harsh discipline, false accusations, a feeling of being pent in, stifled.

A polarity that arises naturally in this melange of fact and fiction is that between the daytime world of ordinary preoccupations and the night world of dreams, fantasies, wild terrors, madness, death. This tension is nearly as intense in the early stories (up to the spring of 1956, which seems to mark some sort of turning-point in her psychic life) as in the later ones -- and, in fact, madness and related topics have a relatively low profile in the prose produced closest to the author's death -- polished and somewhat contrived pieces in which, sometimes, a sensitive reader may feel the writer's effort to keep a lid on, to present a sunny exterior. This is a literary mistake (though the personal motivations may have been sound), because Plath's fiction functions best as poetry, in terms of texture, symbolism and subconscious probing.

At their best (in the late 1950s), the stories scorn such an effort, yield fully to the urge for self-revelation and profit enormously from the real though ambiguous benefits thereof. "Johnny Panic" and "The Daughters of Blossom Street" are two such stories, clearly based on Plath's experiences as an employe of the Massachusetts General Hospital. But the best of all is "Stone Boy With Dolphin," written a bit earlier and paralleling in some details her notebook entries on student life at Cambridge.

The world of this story is largely that of the author's unconscious -- the fairly straightforward events are wrapped in a dream atmosphere and take place in a landscape of coldness, fear, rigid rules, loneliness, violence and strange, hulking symbols. An act of love takes place midway, described so sketchily that the story is told chiefly in symbols: "Inert, she lay staring toward the high ceiling crossed by the dark wood beams, hearing the worms of the ages moving in them, riddling them with countless passages and little worm-size labyrinths." In later pages, the worm symbol is transformed: "a splinter entered her index finger, but she kept her hand sliding down along the rail, right into it. Unwincing. Here. Strike home." Earlier, it had been the spiked top of a fence: "Would it hurt? Would she bleed at all? Because the spikes were going through her hands, and her hands were so cold she couldn't feel them."

This story is probably the book's most fully worked-out essay in a special and fascinating kind of symbolism, but there are many others -- usually simpler and more transparent: "The Wishing Box," for example, in which a wife who doesn't "dream anything" is jealous of her husband's lavish, precise, Technicolor dreams.

One feels almost like an intruder, venturing thus into the mind of a dead woman, though most of the material in this book was written with publication in mind and some was in fact published during Plath's life. But whatever may be said of the motives behind the publishing and the reading of this collection, it is constantly and undeniably fascinating. As fascinating, I suppose, as the dreams of psychiatric patients were to the heroine of "Johnny Panic," who obviously is Sylvia Plath.