naturae” appear as synonyms. For the preacher the book 
     of nature must figure with the Bible as a source of 
     material.

     However, it is in Dante himself, according to Curtius (p. 
326), that “the entire book imagery of Middle Ages is brought 
together, intensified, broadened . . . from the first paragraph of 
the Vita Nuova  to the last canto of the Divina Commedia .” In 
fact, the very concept of summa  inherent in all medieval 
organization of knowledge is the same as that of textbook: 
“Now to reading conceived as the form of reception and study, 
corresponds writing as the form of production and creation. 
The two concepts belong together. In the intellectual world of 
the Middle Ages they represent, as it were, the two halves of a 
sphere. The unity of this world was shattered by the invention 
of printing.” (p. 328) And as the work of Hajnal showed earlier,