Which side is up?

[420benz]

These are roots of a trumpet vine. I don't know how to plant them

 

[Sheal]

If they are definitely roots and not cuttings I would plant them horizontally.

 

[Marck]

The trumpet vine pictured is Chinese Trumpet-creeper (Campsis grandiflora), in the Trumpet-vine Family (Bignoniaceae), native to eastern China and Japan. I agree these root cuttings should be planted horizontally about an inch below the soil surface. You may also find it beneficial to start them in containers where you can monitor their initial growth before planting them in-ground in the Spring.