The sorus of Polypodium virginianum: some aspects of the development and structure of paraphyses and sporangia

Abstract

A comparative study of the ontogeny of sporangia and paraphyses showed that these organs are homologous, with divergence in structure and function occurring after several divisions in the initials of these organs. Paraphyses develop an elongated stalk bearing several vesiculated cells, most of which bear appendages or glandular hairs. Sporangial initials form stalks that subtend the sporangium or spore case enclosing cells which undergo meiosis to form spores. The stalk and vesiculated cells of each paraphysis have a rather complex cytoplasm in the early stages of ontogeny, but ultimately these cells become vacuolated with large deposits of tannins. The tannin bodies originate in small cytoplasmic vacuoles which appear to fuse, forming larger vacuoles with tannin deposits. Stalk and annulus cells of the sporangia also form vacuoles with tannin inclusions. The appendages of the vesiculated cells remain cytoplasmic much longer than the subtending vesiculated cells, but eventually they vacuolate and form tannins as well. It is suggested that the paraphyses perform a protective function for the developing sorus to prevent the loss of water from the developing sporangia.