Yep, its roots like 001100010010011110 said.
If there no rootspace in the bottom, they grow roots way upper to cover more area. This roots work so well, because
-they can also stabilize your plant,
-absorb nutrient built ups from the surface,
-will assist the 02 input of your plant
-and also helps them to outgrow other unwanted new plants around, if your outdoor.
Overall: They banging.
Happy Growing!