In the early 19th century, the fertile delta of northwest Mississippi gave rise to a thriving cotton industry. As White cotton planters turned profits, Blacks toiling in their fields turned to singing and hollering to lighten their load, pass the time, and communicate with each other. Early Mississippi Delta blues songs reflect Southern Blacks' struggle to cope with racial oppression, illiteracy, and poverty. As worksongs grew in length and complexity, blues music moved from the fields to juke joints. Musicians like Charley Patton, Son House, and Robert Johnson accompanied their harsh, raspy vocals (sometimes spoken rather than sung) with powerful, driving rhythms on the guitar or harmonica. The Delta blues style continues to be characterized by raw vocalizing and rhythmic intensity. In addition, Delta blues musicians often employ slide techniques, meaning they move a glass or metal tube called a slide along a guitar's strings to change the notes.