This rather messy looking pile of...straw?...is actually a really close up view of cottolin (purple) and cotton (pale blue) woven together. It is hard to make out but the purple yarn is a two ply - if you look really closely, you might be able to see the one ply of purple on the surface with the other ply in the background. Look for the shadow of the ply.
Cottolin is a blend of cotton and linen. In terms of fibres, they have different characteristics. Some people think that blending them together improves both; others think it brings out the worst in each!
Cotton fibres are from the seed pod of the cotton plant. When harvested the 'tube' of fibre collapses into a flat ribbon which twists. The pale blue fibre in the foreground probably shows this the best. (Do click on the photo for a bigger view.)
Linen fibres come from the stalk of the flax plant and fall into the category of 'bast' fibres. In order to blend the two fibres, the flax fibres are cut up into a shorter length, close to the staple length of the cotton. In the photo, the much darker fibres are the flax while the lighter shade of purple are the cotton fibres.
In preparation for the Next Big Project, I bought a little digital microscope. This is about as far as it will go in terms of magnification. It's still not enough to easily see the structure of the fibres. However, there is a possibility of getting some images from a scanning electron microscope. I'm hoping to get cross sections of the fibres as well as just an enlargement of the fibre.
Knowing the inherent characteristics of the fibres means having the knowledge to choose materials wisely. The more I know about the fibre, the better.