Sentence:  Drawings and pictures are more than mere <WSD>ornaments</WSD> in scientific discourse. Blackboard sketches, geological maps, diagrams of molecular structure, astronomical photographs, MRI images, the many varieties of statistical charts and graphs: These pictorial devices are indispensable tools for presenting evidence, for explaining a theory, for telling a story. 
Meaning of the word marked with <WSD> tags:  (element of decoration) An element of decoration; that which embellishes or adorns.