Pil' shchikov, F.N.; Ignat' ev, N.N., 1973: Absorption of oxygen by apple roots and by soil. Izvestiya Timiryazevskoi Sel' skokhozyaistvennoi Akademii (4): 124-129
Absorption of O2 by apple roots was several hundred times greater than that by soil without any roots in it. Fibrous roots absorbed 1.7 times more O2 than conducting roots.