Johann Horkel, Schleiden's uncle, encouraged him to study plant embryology. He soon developed his love for botany into a full-time pursuit. Schleiden preferred to study plant structure under the microscope. As a professor of botany at the University of Jena, he wrote "Contributions to our Knowledge of Phytogenesis" (1838), in which he stated that all plants are composed of cells. Thus, Schleiden and Schwann became the first to formulate what was then an informal belief as a principle of biology equal in importance to the atomic theory of chemistry. He also recognized the importance of the cell nucleus, discovered in 1831 by the Scottish botanist Robert Brown, and sensed its connection with cell division. He became professor of botany at the University of Dorpat in 1863. He concluded that all plant parts are made of cells and that an embryonic plant organism arises from the one cell. He died in Frankfurt am Main on 23 June 1881. "Die Entwickelung der Meduse" ("The Development of the Medusae"), in Schleiden's "Das Meer"  Schleiden was an early advocate of evolution. In a lecture on the "History of the Vegetable World" published in his book "The Plant: A Biography" (1848) was a passage that embraced the transmutation of species. He was one of the first German biologists to accept Charles Darwin's theory of evolution. He has been described as a leading proponent of Darwinism in Germany. Dot matrix printing  Dot matrix printing, sometimes called impact matrix printing, is a computer printing process in which ink is applied to a surface using a relatively low-resolution dot matrix for layout. Dot matrix printers typically use a print head that moves back and forth or in an up-and-down motion on the page and prints by impact, striking an ink-soaked cloth ribbon against the paper, much like the print mechanism on a typewriter or line printer. However, a dot matrix printer is able to print arbitrary patterns and not just specific characters. The perceived quality of dot matrix printers depends on the vertical and horizontal resolution and the ability of the printer to overlap adjacent dots. 9-pin and 24-pin are common; this specifies the number of pins in a specific vertically aligned space. With 24-pin printers, the horizontal movement can slightly overlap dots, producing visually superior output ("near letter quality" or "NLQ"), usually at the cost of speed. Dot matrix printing is typically distinguished from non-impact methods, such as inkjet, thermal, or laser printing, though they too may use a bitmap to represent the printed work.