Is this cotton or viscose? I have to examine the exact material of a specific fabric (non-woven), of which I know is either viscose or cotton. I know that viscose and cotton are structurally similar, but there should be a way to tell them apart.

This is the result of the microscopic examination (x 100):


My professor tells me this is viscose, but I thought of cotton because of the long fibers. But I also know that cotton has a 'twisted' look under the microscope. 

My professor doesn't give any more clues, which leaves me with a bit of a problem. How can I tell the two apart? Does the picture show enough evidence for viscose (because of the linear structure)? I would like to double check this, just to be sure.
Yes, the picture should be sufficient to decide between viscose and cotton; see photo of cotton at http://whrhs-forensic-chem-spring-2010.wikispaces.com/Fiber+Analysis?responseToken=906bf6a76a5e268a00e54c8bce6927ba.

Recall that cotton was the cell wall of a plant cell, so it retains some of the shape of the cell. (Silk, on the other hand, is excreted from spinnerets, as are man-made fibers, so it looks more like viscose).