Griffith's R strain of pneumococcus is called rough because it:

1. The names describe how the colonies look under magnification. 2. The R strain is non-pathogenic and is called rough because its outer surface is a cell wall and lacks a capsule. 3. As a result the cell surface appears uneven under the microscope. 4. The S strain has that capsule, so it has a smooth appearance instead. _Source: OpenStax Biology for AP(R) Courses (CC BY 4.0), Ch 14 'DNA Structure and Function', sections 14.1-14.6_