HAL BORLAND'S BOOK OF DAYS

366 (this was Leap Year, remember?) dated entries concerning the earth's diurnal round with all that is thereon, as observed by the author from rural Connecticut. In addition to brief nature essays of the sort Borland writes for the New York Times, there are segments of an extended meditation on the relation of man as a ""unique form of life"" to other forms. Borland discusses evolution with the bits of popular science and theory a lively conversationalist might toss up on a porch of a lazy summer evening. Among the thoughts-to-tinkle-your-glass-by: there's such a close structural relation between hemoglobin and chlorophyll that a few atoms of iron in the vital fluid marks a man from a stalk of corn; the ""nervous energy"" which comes from warm-bloodedness is basic to intelligence; if the purpose of nature is persistence, the insects win hands down; man could have been the result of mutations ""blasted into being"" by solar radiation eons ago. In addition to such random talk, there are general and particular views of the main presences along the evolutionary trail, from one-cellers to us, and assorted trivia: e.g. according to Jefferson's thermometer, it was 73.5 degrees at 9 P.M. in Philadelphia on July 4th (try to forget that one). For the predisposed, including the drenched subway rider who reads on June 25th: ""Over at the lake today we found the harebells in bloom. . . .