Before the Spanish-led defeat of the Aztecs in 1521, manuscripts were ubiquitous in Mesoamerica. Regrettably very few survive. One of them is the Aztec (Eastern Nahua) Codex Borgia painted in the Late Postclassic period (ca. 1250-1521 CE). Many of its 76 pages include maize imagery in polychrome. The plant appears amid gods of fertility hovering above naked females; associated with Quetzalcoatl, the god of wind; and rendered to look strikingly similar to grass. The questions I address in this dissertation relate to the significance of maize, Quetzalcoatl, and grass depictions. What does maize imagery convey? Why did the Nahua venerate a god of wind? How is maize related both wind and grass?Until now, scholars of the Codex Borgia have generally assumed that it records information used in divination, astronomy, and farming. What has not been considered is the possibility that it reflects scientific information about plants. I contend that maize imagery studied against the scientific record on plant domestication indicates that it does. Scientists have demonstrated that Central Mexicans were brilliant at manipulating plants, and had by approximately 6,000 BCE, through genetic selection, transformed a common grass into the maize plant. The result was a symbiotic relationship between maize and humans. Amerindians cared for the plant, continuing to manipulate it to become the modern crop, ultimately spread throughout the world, completely dependent on humans for reproduction.Scholars have lamented that indigenous people failed to make a record of their scientific achievements. I argue that maize and related images in their extant artifacts reflect those accomplishments. My research strives to shed light on the Codex Borgia, its imagery, and the ways in which indigenous people of Mesoamerica recorded scientific information. Specifically, my dissertation shows with substantial scientific, ethnohistoric, and iconographic evidence that the Nahua understood plant sexuality, that wind was the primary means of plant reproduction, and that the common grass they held in great esteem was the progenitor of maize. My dissertation seeks to establish that the Codex Borgia's imagery shows the cultural importance of maize to the Nahua and that it was rooted in scientific understanding.