During the late summer of 1855, Gray made his third trip to Europe. This was an emergency trip to bring his ill brother-in-law home from Paris. Gray spent only three weeks in London and Paris, and on the way back he read the newly published "Géographie botanique raisonnée" by Alphonse deCandolle. This was a ground-breaking book that for the first time brought together the large mass of data being collected by the expeditions of the time. The natural sciences had become highly specialized, yet this book synthesized them to explain living organisms within their environment and why plants were distributed the way they were, all upon a geologic scale. Gray instantly saw that this brought taxonomic botany into focus.