Text and pictures share the responsibility for storytelling in picture books (Bishop and Hickman, 1992). Purists often define picture books as those books in which text and picture work interdependently, the visual and verbal are integrated, and pictures and text blend perfectly to tell a story. Pragmatists tend to include in the picture book genre all books that have a picture book format: 24 and 48 pages, pictures on every double page spread, and a brief text with equal space taken up by the pictures. Alphabet books are an important part of the picture book genre because concepts are communicated through both text and illustrations.
Kormanski, L. M., & Stevens, C. B. (1993). Alphabet Books Can Be Used With Fluent Readers and Writers. Reading Horizons, 34 (1). Retrieved from http://scholarworks.wmich.edu/reading_horizons/vol34/iss1/5