These “crosshatched” abstractions, as they are known, confounded critics and fellow artists — is this the same guy who painted the Stars and Stripes? — when Johns debuted them 50 years ago, at Castelli Gallery in 1976. Now Gagosian, in partnership with Castelli, is devoting the last show at its Madison Avenue location (Michael Bloomberg’s moving in) to these turning-point pictures, with an ample and very affecting display of 15 paintings and about as many drawings. Spanning two floors, this exhibition includes examples from every major series of Johns’s crosshatched phase, and culminates with an extraordinary assembly of his three greatest and saddest abstract works, each titled “Between the Clock and the Bed” (1981-83) and each lent by a major museum. (Many other works here are on loan from Johns’s own collection.)