How do you summarize 50 years of performance in 105 minutes?

Pennsylvania Ballet, celebrating its half-century this year, did it Thursday night with a mini-tour of its repertory as it opened a four-day run at the Merriam Theater.

The program began with "Serenade," one of the company's signature ballets. Founder Barbara Weisberger was a child in 1935 when she sat under a piano at the newly formed School of American Ballet and watched George Balanchine create it. The choreographer later gave "Serenade," along with a number of his other masterpieces, to Weisberger to get her young troupe on its feet.

"Serenade" looked as fresh as ever, with a large cast in puffs of blue tulle forming geometric patterns to Tchaikovsky's Serenade for Strings in C (Op. 48). Audience members cried out at the announcement that Amy Aldridge wouldn't be dancing in this ballet as originally planned, but a confident Brooke Moore soon made them forget their disappointment.

On the other end of the night was the company premiere of Jiri Kylian's "Petite Mort," set to Mozart, a modern piece danced in ballet slippers and beige trunks, with corsets for the women. The men brandished swords, balancing them on their fingers, slicing the air, controlling them with their feet. The women, in turn, wielded large black dresses that turned out to be sets rather than costumes. It was a fun, sexy, humorous piece that looked good on the young cast.

In between were two duets of middling success.

"Afternoon of a Faun" is a beautiful Jerome Robbins ballet, which had its company premiere in 2010. It is set in a dance studio, to Debussy, with the audience serving as the mirror. Thursday night, Jermel Johnson was the Faun, stretching and practicing when a nymph, Julie Diana, strutted in.

Their meeting should have been a magical moment, but Diana and Johnson did not connect. Also, Diana's leg extensions did not stretch as far as the role requires to make her seem anything beyond human.

"Under the Sun" saw Alexandra Hughes plucked from the corps for a pas de deux with principal dancer Ian Hussey. Margo Sappington choreographed the piece in 1976 for a Pennsylvania Ballet gala to honor Alexander Calder, and it became an iconic work for the company for many years.

The ballet, to music by Michael Kamen, is a nod to Calder's sculptures, toys, and circus, and had Hughes and Hussey, dressed in fanciful orange-and-white and blue-and-white costumes, performing amusing, difficult lifts. Their movements were correct, but rough transitions made it look more a chore than an acrobatic amazement.