Abstract
The thermo-osmotically driven air stream that temporarily ventilates the plant body of Nelumbo nucifera, supplying rhizome and roots with oxygen, takes its way through interconnected canals and caverns. The course of this circulation, starting with the uptake of gas through leaf stomata and ending with its expulsion via the specialized navel (“central plate”) of the leaves, as well as organs regulating the circuit, were examined using anatomical, pneumatic, and silicone casting methods. The aerenchyma of the peltate leaf, closely paralleling the nervature, is divided into four separate domains: two mirroring lateral halves including halves of the central plate, and each half again separated into an adaxial (basal) and abaxial (distal) sector. Gas absorbed by the adaxial sectors flows through a definite pair of pipes down the petiole into three lateral pairs of the eight main tubes of the horizontal shoot. There it passes several nodes with adjoining leaves, where homologous ducts, arranged in series along the shoot, contribute to the gas flux in its basipetal course. A reverse gas flow, confined to another pair of cauline pipes and also arranged in series, enters in the nodes another pair of petiolar pipes that directly lead to the foliar central plates, where it is released through stomatal pores. These pores are three times as large as the laminal stomata and control the gas release by opening and closing. Each abaxial leaf sector is, apart from its ducts leading down the petiole, via a shortcut connected with the upstream pipes supplying the central plate, so that its air circuit, when active, is only intralaminar and does not join the entirety of the system. The question where, and how, the two downstreaming currents merge into the two upstreaming ones remains unresolved. The structure of the two types of air canal diaphragms, petiolar and nodal, are documented by SEM.
Published Version
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