Population equilibria and stability in plant-animal pollination systems

Differential equation models of the change in population size with change in time have provided valuable insight into nature and have served as tools for management of both predator-prey and competition systems. Presented here is an extension of the differential equation models for application to pollination ecology plant-animal interactions. Analyses define conditions for equilibria and for equilibrium stability for a one-plant one-animal pollinator system. Predictions about plant speciation and pollinator foraging behavior are discussed.     

Cloned nodulation genes of Rhizobium leguminosarum determine host-range specificity

Summary Three nodulation-deficient (nod) mutants of Rhizobium leguminosarum were isolated following insertion of the transposon Tn5 into pRL1JI, the R. leguminosarum plasmid known to carry the nodulation genes. DNA adjacent to the nod: Tn5 alleles was subcloned and used to probe a cosmid clone bank containing DNA from a Rhizobium strain carrying pRL1JI. Two cosmid clones which showed homology with the probe contained about 10 kb of DNA in common. The R. leguminosarum host-range determinants were found to be present within this 10 kb common region since either of the cosmid clones could enable a cured R. phaseoli strain to nodulate peas instead of Phaseolus beans, its normal host. Electron microscopy of nodules induced by Rhizobium strains cured of their normal symbiotic plasmid but containing either of the two cosmid clones showed bacteroid-forms surrounded by a peri-bacteroid membrane, indicating that normal infection had occurred. Thus it is clear that this 10 kb region of nodDNA carries the genes that determine host range and that relatively few bacterial genes may be involved in nodule and bacteroid development.     

Recovery from a viral respiratory tract infection. IV. Specificity of protection by cytotoxic T lymphocytes

Immune spleen cells enhanced for influenza-specific cytotoxic activity after exposure to virus-infected stimulator cells in vitro effect recovery when transferred to nude and immunocompetent mice with influenza pneumonia (5). This protective effect correlated with the virus-specific cytotoxic activity of the transferred lymphocytes and is removed by treatment with anti-0 serum and complement. The experiments presented here indicate that spleen cells taken directly from mice undergoing a primary or secondary infection are less protective than immune spleen cells that are restimulated in vitro before transfer. This decreased ability to clear pulmonary virus and effect survival correlated with their relatively lower levels of influenza-specific cytotoxicity. Protection did not correlate with the level of natural killer cell activity of transferred cells. The results also indicate the immune spleen cells that are protective are influenza A subtype cross-reactive and are H-2-restricted; H-2d immune spleen cells effected recovery of H-2d but not H-2k challenged mice.     

New Method of Isolating Salmonellae from Milk

The use of a cotton gauze swab and subsequent culture of the swab was found to be a more sensitive method for isolating Salmonella from liquid milk than the revised procedure of North. The swab method was found to be as sensitive as the North procedure for recovering Salmonella when incubated at 37 C but more sensitive when incubated at 43 C. Incubation of the swab cultures at the elevated temperature of 43 C gave good results when Salmonella was present at levels as low as one per liter. Swabs exposed to milk contaminated with 100 Salmonella per liter remained positive even when subsequently washed for 2 hr in noncontaminated milk. Bismuth sulfite agar and Brilliant Green sulfadiazine agar were equally effective for isolating Salmonella from broth cultures; use of both media resulted in maximal isolations.     

Mechanism of Antiviral Activity <Emphasis Type="Italic">in vivo</Emphasis> of Polycarboxylates which induce Interferon Production

SYNTHETIC polycarboxylates have been reported to impart resistance to viral infection to experimental animals^1–8. Injection of these polyanions induces interferon^1–3,5–9, to which it therefore seemed logical to attribute the antiviral effect. The high degree and long duration of protection, however, are not in accord with the low and transitory levels of interferon induced, suggesting that mechanisms other than interferon are involved. Certain polyanions have been found directly to inactivate virus or to inhibit its adsorption to cells¹⁰in vitro. This may delay the development of viral infection in vivo. Stimulation of reticuloendothelial cell activity, as demonstrated by increased phagocytosis induced by pyran copolymer¹¹, may deviate virus from its target cells.     

Abnormalities in synaptonemal complexes in pollen mother cells of a lily hybrid

Two abnormalities, one in lateral elements of synaptonemal complexes the other involving whole complexes, have been studied with the electron microscope in pollen mother cells of the lily hybrid, Lilium aureliensis × L. henryi, which with the light microscope showed almost complete bivalent formation at metaphase. Brief water treatment of pollen mother cells prior to fixation, revealed that the aberrant configurations in lateral elements arose by breakage and subsequent folding of severed fragments up to about 0.8 m long. The abnormality ocurred at recognisable heterologous regions, apparently immediately after pairing. The folded fragments were eliminated from the chromosomes at some time during pachytene. Pseudo pairing was observed after synapsis between either more than one pair of homologues or one pair bent back on themselves, so as to produce polycomplexes. Seemingly, central elements could develop between lateral elements on their outer face under these conditions.     

Gas-liquid chromatographic analysis of cyasin in cycad flour

A method for the quantitative determination of cycasin from cycad flour by gas-liquid chromatography is described. The flour is extracted with 70% ethanol and the residue from the dried extract is directly trimethylsilylated. Androsterone was found to be an excellent internal standard. The average content of cycasin from ten separate analyses of one lot of flour was $\text{0.429 gm}\text{100 gm}$. The method is rapid, sensitive, and not hindered by contaminating compounds.     

A new species of Polymnia (Compositae: Heliantheae) from Mexico

Polymnia mcvaughii from Jalisco, Mexico, is described as new. This herbaceous species appears to belong in the mainstream of evolution within the genus. It exhibits marked affinities to several species, but most closely resemblesP. oaxacana Schultz-Bip. Illustrations of important features are included, along with a list of key characteristics.