This question is about roots that grow upward, against gravity, purely to help the plant breathe. Think about where a plant would need this trick: soil so waterlogged that normal roots cannot get enough oxygen.
- Pillar roots: These grow straight down from horizontal branches, as in the banyan tree, and their job is extra mechanical support, not respiration, so they do not fit.
- Stilt roots: Seen in maize and sugarcane, these grow obliquely from lower nodes to prop up the stem. Again the purpose is support, not gas exchange.
- Pneumatophores: Mangrove and marsh plants growing in oxygen starved, waterlogged soil send special roots upward, above the mud or water line. These carry pores called lenticels that let atmospheric oxygen diffuse down to the buried root system.
- Velamen roots: Found in epiphytic orchids, these aerial roots are wrapped in a spongy velamen layer that soaks up moisture and some nutrients from humid air, not oxygen for a submerged root system.
Only pneumatophores combine the two features the question asks for, growth against gravity and a role in supplying oxygen, so that is the answer.
Let's summarize:
- Pillar and stilt roots: mechanical support, not respiration.
- Pneumatophores: negative geotropism, lenticels for oxygen uptake in waterlogged soil.
- Velamen roots: moisture absorption in epiphytes, an unrelated function.
So the roots described are pneumatophores.