Anatomy of the gas canal system of Nelumbo nucifera

Nelumbo nucifera (Gaertn.) grows by extending a creeping rhizome through anaerobic sediments. Nodes form at intervals along the rhizome, each producing a single leaf, and gas canals channel air from the leaves throughout the petioles and rhizomes. The gas flow pathway was mapped by casting the canals in growing shoots with silicone and by blowing air through complexes of rhizomes and petioles. Air from a leaf flows to a rhizome through one of two petiolar canal pairs, joining with the lowermost of three canal pairs in the rhizome through a chamber in the node. The lowermost canal pair links these nodal chambers along the length of a rhizome, allowing air from a node to flow both forward, toward a growing shoot, and backward, toward preceding leaves. These linked chambers also connect with the middle pair of canals on their proximal side, enabling flow to proceed backward along the rhizome to an adjacent node. A chamber in the next node then diverts the flow into the upper canal pair. This pair leads to a third node and chamber from which the air vents to the atmosphere through the second petiolar canal pair. Thus, pressurised air from one leaf must flow backward through two nodes before it returns to the atmosphere. Forward flow also ventilates a shoot's growing tip, with air from the lowermost canal pair entering a chamber in the developing node which, as described above, connects with the middle canal. This allows the air to reverse direction at the tip and enter the vent flow pathway.