Each turn of the page reveals a species from within the current family's section. The left page has the scientific and common names at the top in 3 languages - English, German, French - with a brief description of some of its properties below in the same languages, one language per column. The right page shows the wood of the species cut in 3 directions: transverse (crosscut), radial (quartersawn), tangential (flat or plain sawn).
In the original editions of this book, assembled by Romeyn Beck Hough between 1888 and 1913 in 14 volumes, the woods - reproduced in print here - were actual veneer-width samples of wood from the original species, cut in the directions listed above into 2"×5" rectangles and mounted on card stock. I believe the left page is new information not in the original book, as the new information reflects changes to the taxonomic classification (species name, etc) shown in the century-old text surrounding the prints of Hough's wood samples.