Between 1543 and his death in 1566 physician and botanist Leonhard Fuchs composed an expansion of De historia stirpium that he planned to have published in three volumes with a greatly expanded text and 1525 images, including descriptions of 400 plants "not mentioned by the ancients or completely unknown." However, in the interval Fuchs's publisher, Michael Isengrin, died, and Isengrin's widow was unwilling to advance the very substantial sum, known from Fuchs's correspondece to be 3000 florins, to publish the work. Thus, by the end of his life Fuchs had devoted to an enormous amount of time, effort and expense to writing a work that was never published. Remarkably, the manuscript passed down through Fuchs's family, and resisted several efforts to have it published over the centuries, and survived two world wars, before it appeared for sale at a congress of the International League of Antiquarian Booksellers in Vienna in 1954, where it was purchased by the National Library of Vienna.
In the commentary volume to their edition of The Great Herbal of Leonhart Fuchs (1999) Meyer, Trueblood and Heller devote chapter 5 (pp. 147-194) to Fuchs's unpublished manuscript, which they call "The Vienna Codex." The National Library of Vienna's official name for the manuscript is Codex Vindobonensis Palatinus 11 122. From Meyer, Trueblood and Heller's description on pp. 154-55 I quote:
"It now consists of nine small folio volumes, 4,444 pages of text and figures, with a page size of 31.5 x 20.8 cm, bound in richly ornmaented early-seventeenth century white pigskin. The Latin text is wrtten in the small italic hand of Fuchs; the plant pictures are hand-colored. The manuscript is still in good physical condition, but many of the water-colored pictures have faded because of age. Some of the illustrations suffered when the manuscript was put into its present binding, because of trimming at the top of the page, although the loss is not serious.
"The Vienna Codex includes all of the original 511 figures from the Historia of 1542 and 6 more from the German edition of 1543. In addition, there are 1,012 new figures, bringing the grand total of plates in the Codex to 1,529 by our count, although Fuchs mentions 1,525 on his title page. There are a few duplicate plates, making an accurate count more difficult. The number of plates does not reflect the number of species and other categories represented in the manuscript. Sometimes more than one species is figured on a plate, bringing the number of plants figured to ca. 1,541 in the manuscript. The count is provisional, however, until all the plants have been identified...."
When I wrote this entry in November 2013, to the best of my knowledge, Fuchs's manuscript remained the only major surviving unpublished autograph manuscript by a Renaissance scientist of the first rank.