Platyamoeba stenopodia. n. g., n. sp., a Freshwater Amoeba*

SYNOPSIS. Platyamoeba stenopodia n. g., n. sp., isolated from a lake in Alabama, is an amoeba with flattened form, usually more than 2.5 × as long as broad, the anterior half hyaline and the posterior half granular, with a single vesiculate nucleus at the posterior edge of the hyaline region. It forms a transitory floating stage with slender, hyaline pseudopods. Its cyst is spherical, uninucleate, with a smooth inner wall and a thinner, closely applied outer wall, which is often slightly wrinkled. Length of locomotive amoeba 15–36 μ diameter of cyst 7–11.5 μ Reproduction by binary fission with mesomitotic nuclear division, the nuclear membrane disappearing in prophase. The genus Platyamoeba is erected for amoebae including this organism; the type species is P. placida.     

The world in a grain of sand: evolutionarily relevant,small‐scale freshwater bioregions on subtropical dune islands

1. Conservation plans are required to safeguard freshwater biodiversity in the face of increasing threats. Traditionally plans have used surrogates for biodiversity that do not account for the evolutionary process, but genetic data in the form of comparative phylogeography can fulfil this role. 2. Comparative phylogeographic analyses of multiple freshwater fish and decapod crustacean species were carried out with specimens from two model systems, namely the sand dune islands of Fraser and North Stradbroke in eastern Australia. 3. Almost all of the species studied from both islands displayed an intraspecific evolutionary split between sides of the island (east/west on North Stradbroke Island, and north/south on Fraser Island), indicating that each side of each island hosts its own distinct community of populations of freshwater animals. 4. The probable process responsible for both of these divergent communities is different source populations for each side of each island. 5. This study shows that biodiversity will not always follow obvious geography and that significant diversity may exist at small scales within multiple species. These evolutionarily relevant units of biodiversity should be incorporated at the beginning of the conservation and resource management planning process.     

The Diffusion of KCI from Micro-electrodes

The diffusion of salt from the tips of 3 M KCI filled micro-electrodesis measured. The leakage of KCI in 3 min is found to be 5.70x 10^–12–1.08 x 10^–11 mol for tips of 0.2–0.6µm diameter, and 2.70 x 10^–11 mol for tips of 0.6–1.0µm diameter. The observed leakages compare with estimatesbased on the diffusion coefficient of KCI and micro-electrodegeometry. The results confirm that the use of 3 M KCI in micro-electrodesmay lead to serious contamination of impaled cells providedthe electrode tips remain unoccluded.     

Rates of production and internal levels of ethylene in the vegetative cotton plant

The internal levels of ethylene in and the production ratesof ethylene by various parts of the cotton plant {Gossypiumhirsutum L. cultivar Acala 4–42) were determined by separatetechniques. Wounding of tissue, which resulted from both techniques,increased ethylene production. A peak in wound-induced ethyleneoccurred around the second to third hour after wounding andgradually declined until the sixth or seventh hour when ethyleneproduction began to level off. Using two techniques, with numerousobservations from each technique, ethylene levels were foundto be relatively uniform throughout the vegetative cotton plant.There was a small trend for levels of ethylene to increase fromthe bottom (oldest tissue) to the top of the plant (youngesttissue). Of major interest was the observation that the productionrates and internal concentrations of ethylene in the petiolewere two to six times higher than those in the leaf blade. Thisrelative concentration of ethylene in the petiole supports thehypothesis that ethylene is a natural regulator of abscissionwhich acts, in part, through modification of auxin transport. ¹ A contribution of die Texas Agricultural Experiment Station.Supported in part by Grant GB-5640, National Science Foundationand grants from the Cotton Producers Institute. The data forthis paper was taken from a Master of Science Thesis by J. A.M. submitted to Texas A & M University January 1970. ² Present address: Department of Agronomy, Purdue University,Lafayette, Indiana, U.S.A. (Received June 29, 1971; )