It is hypothesized that root hairs serve as specialized respiratory cells concomitantly with their other functions. Occurrence of "pores" (unthickened cell walls), presence of little or no cuticle (offering minimum resistance for oxygen diffusion) and dense cytoplasm studded with mitochondria at Ule tip of the root hairs, are some of the special ultrastructural adaptations of root hairs which offer an indication that at least one of their main functions involves respiration. This hypothesis is based on ultrastructural evidence and comparative anatomy such as: (1) development of more dense root hairs in soil voids, (2) occurrence of dense root hairs on the juvenile primary root of viviparously germinating seeds inside the pod (e.g., Pisum sarivum and Phaseolus vulgaris seedlings grown in paper towel and glass culture); (3) occurrence of permanently open stomata in the root hair zone of some species which is believed to be a double advantage as it may enable additional diffusion of oxygen to meet greater energy requirement of growing seedling; (4) occurrence of well developed root hairs in most of the terrestrial plants and their absence or poorly developed nature in most hydrophytes; and (5) development of maximum number and length of root hairs in relatively dry and porous soils rather than wet soils. Further, the increase in surface area that root hairs provide serves as a sort of "plant gill" to maximize uptake of oxygen as well as water and nutrients.