A Study on Air Chamber Morphogenesis in Some New Zealand Members of the Marchantiales

Abstract

The origin and development of air chambers were studied in eight genera and ten New Zealand species from the Order Marchantiales. The air chambers of all genera and species studied were found to owe their origins to a schizogenous process, which starts with the split beginning either at the surface of the thallus epidermis, between two neighbouring cells which are apical cell derivatives (exogenous), or below the surface at the junction of the epidermis and sub-epidermis (endogenous). In Marchantia polymorpha the air chambers are proposed to develop endogenously, although the tumefaction of the tissues makes it difficult to observe the exact origin beyond a reasonable doubt. In all other genera and species studied, the chambers developed endogenously (Marchantia macropora, Neohodgsonia mirabilis, Riccia fluitans) or exogenously (Lunularia cruciata, Reboulia hemispherica, Plagiochasma rupestre, Marchantia berteroana, Targionia hypophylla, Asterella australis). The ontogeny of the air pore of M. berteroana starts from cells which close the entrance of the air chamber at a later stage of its development, not from a mother cell. The mode of air chamber development was found to vary within the genus Marchantia; In M. berteroana chambers develop exogenously, in M. macropora and M. polymorpha chambers develop endogenously.