1) A cultural experiment was carried out in order to determine the morphology and embryology of either zoospores and gametes of Hormiscia penicilliformis (R_OTH) F_RIES and H. incrassata (K_JELLM.) C_OLLINS.
2) In H. incrassata all kinds of the reproductive cells, namely the anisogametes, macro-and microzoospores are produced in one and the same filament. The macrozoospores are obovoid in shape, 30μ long, l6μ wide, provided with 4 cilia at the anterior end which is square pyramidal in shape, and extending posteriorly into a long tail. The tail is up to 30μ in length. The microzoospores are smaller, ovoid in shape, l6μ long, 10μ wide, with 4 cilia at the anterior end which is not pyramidal, and with a shorter tail.
3) The zoospores appear to be negatively phototactic. On germination they give rise directly to new filaments. Within three weeks the young filaments become composed of ten or more cells and already provided with the characteristic extramaterical rhizoids arising from some of the basal segments.
4) Sexual reproduction by 2-ciliated anisogametes. The macrogametes are spindle-shaped, 14μ long, 6μ wide, and bright green in color, while the microgametes much smaller, ovoid in shape, 4μ long, 2.5μ wide, and pale green.
5) The chromatophore of H. incrassata is coarsely reticulate with many large openings, containing a number of refractive globules, which the writer believes to be nuclei and not pyrenoids as interpreted by previous investigators. The chromatophore changes its form according to the reproductive condition of the segment. The breaking up of the chromato-phore into areolae precede the formation of the reproductive cells as has been described by some authors. In young sporangial segments the nuclei undergo mitotic division repeatedly.