- Why Do Trees Grow in Spirals? (Washington Trails Association)
- A clockwork pine – Now we know why some trees get so wound-up (New Scientist)
- Why Do Trees Form Spiral Grain? (The Gymnosperm Database)
- Function of spiral grain in trees (Kubler, 1991 Trees)
- The cause of the prevalent directions of the spiral grain patterns in conifers (Skatter & Kucera, 1998 Trees)