The pore of the leaf cavity of Azolla: Morphology, cytochemistry and possible functions

Light and transmission electron microscopy were used to describe the leaf c avity pore of Azolla. The morphological analysis of the pore revealed that it remains open during leaf development as well as in mature leaves. As it seems that there is no obstruction of the pore by any mucilage, gas exchang es between the atmosphere and the inner gaseous compartment of the leaf cav ity are likely to occur. The pore, which is cone-shaped and protrudes into the leaf cavity, is limited by two epidermal cell layers. The cells lining the inside of the pore become teat-shaped during pore morphogenesis. Ultras tructural study of these cells showed the presence of a large number of org anelles, paramural bodies and 'wart-like' projections at their cell wall su rface, suggesting a secretory role. Cytochemical stains showed that these p rojections are made up of pectin, callose and protein. The role of the pore as well as the possible functions of the teat-cells and their projections are discussed.