1. The vegetative forms of amebae may be developed in vitro from the cysts. 2. The cysts of Entamoeba tetragena and Entamoeba coli each produce only a single vegetative individual. It has not been observed in vitro that a number of daughter amebae, corresponding to the number of nuclei present in the cyst, emerge from the mother cyst, as claimed by Casagrandi and Barbagallo, Schaudinn, and a nu...

The non-Mendelian mutant d48 of Paramecium tetraurelia contains micronuclear wild type A genes, but at autogamy and conjugation proper processing fails and new macronuclei lack A genes. When cloned A genes are injected into the macronucleus of d48, proper processing is restored at the next autogamy; d48 is rescued, becoming permanently wild type. In the present study we have injected portions o...

The location and extent of local degeneration of cilia during sexual reproduction of Paramecium was studied using scanning electron microscopy to examine cells undergoing conjugation and autogamy. At some time during the mating reaction, but prior to conjugant pair formation, ciliary degeneration begins at the antero-ventral tip of cells and proceeds posteriorly along the suture. In the anterio...

Paramecia cells, like human diploid cells cultured in vitro, provide a useful model system for understanding the mechanism that limits division potential. The reported maxima of the clonal lifespan of Paramecium tetraurelia fall into two ranges: from 220 to 258 fissions and from 310 to 325 fissions. We found that neither the selection of vigorous lines nor the cryptic occurrence of autogamy off...

The factors maintaining the cytoplasmically inherited killer trait in populations of Paramecium tetraurelia and Paramecium biaurelia were examined using, in part, computer simulation. Frequency of the K and k alleles, infection and loss of the endosymbionts, recombination during conjugation and autogamy, cytoplasmic exchange and natural selection were incorporated in a model. Infection during c...

The relation of mortality and the proportion of progeny with reduced fission after autogamy to the clonal age in Paramecium aurelia was investigated. This relation is not linear but the proportion of defective progeny in creases stepwise. The observations are in agreement with those expected from the calculations of the number of deleterious mutations in the micronucleus.

Abstract Plant mating systems may reflect an adaptation to a habitat type, with self-pollination being potentially common in unstable and disturbed conditions. We investigated the reproductive ecology of Alpine, narrow-range toadflax, Linaria tonzigii Lona (Plantaginaceae), occurring steep dynamic mountain screes. explored self-compatibility spontaneous autogamy, seed viability, daily nectar pr...