Porocyclocytic stomata in Christensenia cumingiana Christ (Mariattiacere - Marattiales - Eusporapgiopsida).

Abstract

This paper deals with the epidermic morphology and the peculiar pneumathodes found in the fronds of Christensenia cumingiana Christ (Marattiacere). The epidermic patlem has been found to differ in the abaxial and adaxial surfaces of the pinnae, with frequently sinuous and poligonal to subpoligonal models respectively. (Rolleri & Deferrari 1986). This is similar to the pattem found in especies of genus Danrea l.E. Smith. The pneumathodes are here consider as special type of cyclocitic stomata. Surfaces and cross sections of pinnae had been studied, both in juvenile and adult epidermic areas. As results of the rccording of all the probable slages of development, the genesis stomato can be consider as a perigenous one. The name porocyclocytic stomata is here proposed for the mature pneumathode. This dessignation alludes to its essential characters: the pores are always wide open, while the subsidiary cells are arranged in 2 concentric and superimposed crowns of encircling ceIls. The whole structure protrudes above the adjacent epidermis. The porocyclocytic stomata would function as doubIe structures for gaseous exchange and elimination of liquid water (guttation). They would behave as stomata and, eventually, also as a simple and passive hidathodes - which would be justified by the mesophyll characteristics, the hydric needs of the fronds and the fore ts environment where these plants grow. The porocycIocytic stomala are here considered as a functional specialization ofthe common cyclocytic typeof stomata, generally present in Marattiales sensu lato.