The book, Goethe: Journeys of the Mind, by Gabrielle Bersier, Nancy Boerner, and Peter Boerner, concerns Goethe's immersion in foreign lands without the necessity of leaving the premises of his home. Some of this armchair traveling was in the interest of his poetic production, e.g., West-östlicher Diwan and Chinesisch-Deutsche Jahres- und Tageszeiten. For research, he had access to the Weimar library as well as to scholars of "the Orient." For me, the most interesting chapters of Journeys of the Mind concern his reading and correspondence with scholars and scientists, especially those working in the field of botany and natural science. With Alexander von Humboldt he was on close terms, and they met and corresponded often, both before Humboldt's journeys to the Americas and afterward.
As I mention in my review, by the early 19th century Goethe was Germany's most famous product, and it was not surprising that many scholars traveled to Weimar to share their findings. One of these was Carl Friedrich Philipp von Martius, a professor from Erlangen, who traveled to Brazil in 1817 as part of a scientific expedition of Bavarian and Austrian scientists that accompanied the bridal ship bearing the daughter of the Hapsburg emperor to marry the Portuguese crown prince. The Leopoldina edition of Goethe's scientific writings is named for the archduchess.
Martius's treatise on the natural history and morphology of palm trees complemented Goethe's ideas of plant morphology. Nevertheless, the enigmatic entry in Ottilie's diary entry -- "Es wandelt niemand ungestraft unter Palmen" -- could not have been suggested by Goethe's acquaintance with Martius, as Elective Affinities was published already in 1809. The relationship between Goethe and Martius was obviously of great importance to both men, as can be seen in Goethe und Martius, which includes the correspondence between the two men.
My TLS review was accompanied by a lovely illustration from Mauritius's study of Brazilian vegetation, Historia naturalis palmarum. I include another illustration at the top of this post from a book review of an English translation of Book of Palms that appeared in The Gardening Register.