The article presents the life and work of Konstanty Roman Jelski (1837–1896), one of the eminent, 19th century Polish naturalists and travelers. He significantly contributed to zoological and botanical collections from French Guiana and Peru, carried out his geological work in Poland and in the Southern Hemisphere. Many naturalists benefited from the Jelski specimens for examinations. Numerous species originate their names from his name. The life of K. Jelski was recently presented in the book Konstanty Jelski (1837–1896). Naturalist and explorer of South America (by R. Tarkowski, in Polish). K. Jelski’s life is a story of the fate of a representative of the borderland nobility in the second half of the 19th century, who, following education, became a political emigrant after the 1863 uprising. In search for a job in the learned profession, he first left for the Ottoman Empire, then France and thence South America. After several years of a fruitful stay in French Guiana and Peru, where he collected natural specimens for various institutions in Europe and North America, he returned to Europe. In Cracow, he was employed as a custodian of scientific collections at the Physiographic Commission of the Academy of Arts and Sciences. The article is based on rich, unknown materials of K. Jelski (letters, travel diary) found in the monastery of the Vincentian Priests and Brothers in Cracow. These have been supplemented with documents and information about zoological, botanical and geological specimens retained in several institutions (Warsaw and Cracow) and private collections of the Jelski family. These materials have allowed a verification and a significant broadening of our knowledge about the life and activities of Jelski, known from previous publications. In particular, the material found refers to the period after Jelski’s departure from Kiev (in 1863): his stay in French Guiana and Peru (1864–1879) and in Poland (1880–1896), as well as his cooperation with W. Taczanowski and A. Waga, work for A. Raimondi, contacts with Poles in Peru and Europe, his work in the Physiographic Commission of the Academy of Arts and Sciences in Cracow, geological activities, and details of his private life. The analysed material also brought interesting information concerning the activities of the Zoological Cabinet in Warsaw and the patronage of natural sciences of Konstanty and Aleksander Branicki, the cooperation of Raimondi with Polish naturalists and engineers in Peru, the constraints on and the exploration of neotropical flora and fauna, the life of Polish émigrés in Peru. The collection of K. Jelski’s letters includes more than 360 items held at the Vincentian Priests and Brothers in Cracow, and covers the period of 1864–1890. The letters were addressed to the following persons: Władysław Taczanowski, Antonio Raimondi, Aleksander Miecznikowski (most the letters), E. Boroz, Luis Santa Maria, Juan Gasteki, A. Waga (less numerous) and Aleksander Jelski, Aleksander Bagiński, Botino Jorge, Konstanty Branicki, Jean Luis Cabanis, Tytus Chałubiński, Carlos Gadaro, Abelino Collasa, Hipolit Crosse, Artur Delteil, Henri and Emil Deyrolle, Meletiusz Dutkiewicz, Emil A. de Para, Tilarcio Espinosa, Eli Franconie, Eduard Hartnack, Charles Oberthur,
Ignacy Szyszyłowicz, Antoni Wałecki, August Wrześniowski (several letters) and others. There are also letters addressed to various institutions. The letters arrived from Poland, Russia, France, French Guiana, Peru, Guadeloupe and other places. The travel diary by K. Jelski covers the period of 1869–1875.
