New York City Ballet at Koch Theater Alexei Ratmansky's "Russian Seasons" at the Koch Theater. The real test of a ballet company's health comes not at opening nights or galas, but when injuries remove beloved dancers, or new productions return, or marvelous ballets are revived with alternative casts. All the above were on view this weekend at New York City Ballet. The company's most remarkable ballerina, Sara Mearns, was one of five women featured in Saturday afternoon's performance of Christopher Wheeldon's work "Les Carillons," but after her first pas de deux, the ballet continued with only the other four. Ana Sophia Scheller, one of them, gallantly stepped in to dance Ms. Mearns's solo. Only in the finale did many in the audience become aware that a lead dancer had gone missing. Ms. Mearns suffered a back injury. On Sunday afternoon Maria Kowroski and Tyler Angle replaced Ms. Mearns and Jonathan Stafford in the second movement of George Balanchine's "Symphony in C." Ms. Kowroski, giving her finest performance of the season so far, looked softly spectacular in the famous second movement, with superb partnering from Mr. Angle. In almost every respect, the performance of that ballet was a significant improvement over the one seen at Thursday's gala; "Symphony in C," after almost four years" absence from the company's repertory, has returned to being its most "home" ballet - and the most exhilarating piece in world repertory. At the same performance, Teresa Reichlen and Justin Peck replaced Ms. Kowroski and Ask la Cour in the leading roles of Balanchine's version of "Firebird." Mr. Peck did well; Ms. Reichlen gave the finest interpretation I have ever seen of that part. The all-Balanchine program started with a rapt performance of "Serenade," led by Janie Taylor, Sterling Hyltin and Rebecca Krohn. Although some of the conductor Fayçal Karoui's tempos in "Serenade" and "Symphony in C" were exceptionally fast, both orchestra and dancers rose glowingly to the challenge. Saturday evening's triple bill of 21st-century ballets, all done to modern music, included an enthralling revival of Alexei Ratmansky's beautiful and moving "Russian Seasons." At such times, it is worth giving credit to the company's ballet master in chief, Peter Martins. For 25 years he has been the recipient of constant criticism, and the main reason is clear: He is the successor to George Balanchine, the greatest of the 20th century's several great ballet choreographers. Anyone would be inferior. Mr. Martins isn't helped by failures of inspiration in both his own choreography or his casting policies. But I have heard people speak as if the good things at City Ballet all happened despite, not because of, Mr. Martins. So he is to blame when the company, which presents far more new choreography than any other in the world, presents failures; if he introduces the occasional success, well, he was lucky. But Ms. Mearns is only the most striking of four ballerinas who have risen to principal status in the last four years; the others are Sterling Hyltin, Tiler Peck and Ms. Reichlen. Elsewhere, there have been gifted young women whose careers crumbled; but these four keep growing in beauty and artistic maturity. The company's current musical standards are also admirable. Credit must go to Mr. Karoui, the company's music director, but also to Mr. Martins, who hired him. Other companies helped to nurture the choreography of Mr. Wheeldon and Mr. Ratmansky, but there must be a reason that they have made their best works for City Ballet, and Mr. Martins must somehow be connected. I have given a great many bad reviews to Mr. Martins myself; I don't withdraw them. But it is silly and resentful of people to associate him only with the company's downside. He is responsible for both the company's failures and its successes. Both have been pronounced. It's this that makes him one of the most puzzling people in dance today. Further pleasures of this season have come from clever programming and casting. There are structural parallels between Balanchine's "Concerto Barocco" and "Kammermusik No. 2" (two ballerinas working in close duet with the solo instrument; a corps de ballet of eight largely connected to the orchestra). Perhaps the company has previously put both on one program, as happened earlier this season, but never before have the same pairs of women alternated between the two ballets: Ms. Mearns and Ms. Reichlen, or Ms. Krohn and Abi Stafford. Both ballets are in fine shape; "Kammermusik," whose details richly repay multiple viewings, is a tonic to eye and ear. Likewise, it will be fascinating to see Balanchine's two Brahms ballets, "Liebeslieder Walzer" and "Brahms-Schoenberg Quartet," sharing the same program this week and next. What is it about Brahms that prompted Balanchine to use more lifts than in any other ballets? As the Firebird, Ms. Reichlen found a wealth of remarkable detail - sudden changes of direction in midjump; loaded moments of tension as the partnering turned into a struggle for power more psychological than physical; vivid inflections of hands, arms and upper body - and made all of it acutely responsive to Stravinsky's score. Clotilde Otranto conducted a vivid account. On Saturday afternoon Ms. Hyltin and Adrian Danchig-Waring gave compelling performances in the lead roles of Jerome Robbins's "In G Major"; Mr. Danchig-Waring, despite his often too anxious expression, is developing into a valuable artist. Ashley Bouder and Adam Hendrickson led an impetuously playful "Tarantella." In "Symphony in C" the corps's battements tendus still have a mere fraction of the voltage I remember in Balanchine's lifetime, and yet I testify that Sunday's performance was otherwise life-enhancing. Megan Fairchild, with her delicious footwork, found brio in her second solo, to pizzicato music, in the first movement; her partner, Jared Angle, is having altogether his freshest, brightest season in years; in the third movement Joaquin de Luz's elevation kept taking the breath away; and Ms. Peck brought a range of new inflections to her fourth-movement solo, giving one complex pirouette a delivery so ultra-crystalline that it encapsulated the sparkle of the entire ballet. The New York City Ballet season continues through June 10 at the David H. Koch Theater, Lincoln Center; (212) 870-5570, nycballet.com.