Complex sentence: By the end of 1872, Sargent became the first Director of the Arnold Arboretum, a post he held until his death, and Director of the Botanic Garden in Cambridge (long since given up).
Split into simpler sentences: By the end of 1872, Sargent became the first Director of the Arnold Arboretum, a post he held until his death. He was also Director of the Botanic Garden in Cambridge (long since given up).