The Structure and Development of a New Aquatic Phycomycete

Abstract

Among the aquatic Phycomycetes the genus Araiospora of the family Leptomitaceae was first established by Thaxter in 1896 upon the single species A. pulchra, The genus is readily dis? tinguished by the presence of two types of sporangia, one subcylindric with thin, smooth wall, the other obpyriform with thick, spinose wall, and by the formation within the oogonium of a periplasmic layer of hexagonal appearing cells surrounding the central oospore. To this newly erected genus Thaxter at the same time (1896) transferred Cornu's Rhipidium spinosum (1872) because of its spinose thick-walled sporangia, calling this new combination A. spinosa. It remained for von Minden (1915, 1916), however, to add to our knowledge of this scantily described species, for from material collected and studied in Germany he described in detail the developmental stages not only of the spo? rangia but also of the sexual organs hitherto unknown. Since the two foregoing species were both characteristic of temperate regions, Linder's (1926) description of a new species from British Guiana is of interest, for it is the first instance in which a member of the genus Araiospora, or indeed a representative of the entire family, has ever been reported from the tropics. This species, A. coronata, is unique in that the 4 to 6 spines about the apical exit papilla of the secondary sporangia are 7.9 fx in length, whereas in A. spinosa the spines are more numerous and much longer (60-70/x). Although the sexual organs were not found in Lin? der's species, there was ample basis for his establishing it as new since in addition to the distinctive number and arrangement of the spines the sizes of the various organs differed from those of the already established species (see Table 1).