Presence of Amoebae in the Rhizosphere of a Beach Grass1

The occurrence of amoebae in the rhizosphere of a beach grass (Panicum sp.) collected at the Hempstead Lake State Park, Long Island, New York, was investigated throughout the growing season of 198 1. Amoebae achieved increased population density in the root system when compared with that in the surrounding bare sand; moreover, numbers of amoebae were higher only during the period of active plant growth and up to flowering. Following flowering, the numbers of amoebae in the root system fell to the level found in bare sand. The species diversity of amoebae in this system was compared with that in the carposphere of the mushroom Laccaria trullisata which appears at the same site but at a different time of year.     

METHODS FOR THE STUDY OF BLOWFLY POPULATIONS

1. A simple method of radioactive labelling of L. sericata larvae is described.
2. More uniform count levels are obtained in individuals which have fed entirely on radioactive foods than in those which first feed on non-active food.
3. The radioactive count rates of the larvae are correlated with larval live weight and the counting rates of resulting imagines correlated both with corresponding larval counting rates and with imaginal live weight.
4. The loss of ³²P in the larvae due to causes other than decay of the isotope is traced from the prepupal stage to 3 weeks after emergence. The first and major loss occurs at emergence, when about 10% of the original ³¹P is shed as empty puparium and meconium. Adults lose about 1.5% per day.
5. The distribution of ³²P in the adult body of L. sericata labelled in the larval stage has been determined. The abdominal tissues have a lower activity than the rest of the body.     

Carbon Fixation by Paphiopedilum insigne and Paphiopedilum parishii (Orchidaceae),{dagger}

Measurements of stomalal conductance, ¹⁴CO₂ fixation and aciditylevels indicate that Paphiopedilum insigne (Walhch) and P parishii(Rchb f) Stein, Orchidaceae, do not fix carbon via the Crassulaceanacid metabolism pathway Acidity, C₂ pathway, CAM, stomatal conductance     

Dermal Chromatophoies

SYNOPSIS The pigmentation of poikilotherms is based upon thepresence of deimal chiomatophoies melanophores, lndophores,and xanthophores The form function, and composition of eachchromatophore type is discussed, and variations n melano somecomposition are described Recent theories about the mechanismof melanosome movement are discussed The role of mdophores inpigmentation processes is described and their impoitance instructural coloration is evaluated Interrelationships of thepigmentary organelles of all three chromatophores are discussed,and evidence is piesented that they have a common origin Associationsof pigment cells with themselves or with other elements of theintegument are described as i basis for chromatophore function     

Absence of spirochaetes (Borrelia burgdorferi) and piroplasms (Babesia microti) in deer ticks (Ixodes dammini) parasitized by chalcid wasps (Hunterellus hookeri)

An entomophagous wasp (Hunterellus hookeri Howard) parasitizes about a third of the host-seeking nymphal Ixodes dammini Spielman et al. ticks on Naushon Island in Massachusetts (U.S.A.) where the agents of Lyme disease (Borrelia burgdorferi Johnson et al.) and human babesiosis (Babesia microti Franca) are enzootic. Following blood-feeding, wasp-parasitized ticks are destroyed by the developing wasp. The prevalence of either human pathogen in host-seeking ticks collected in wasp-infested sites is nearly 40% lower than that found in other sites. Nymphal ticks, collected early in their season of activity, are more frequently parasitized by the wasp and less frequently by the Lyme disease spirochaete than those collected later in the summer. Spirochaetes never infected wasp-infected ticks, and few wasp-infected ticks were concurrently infected by the Babesia piroplasm. Taken together, these correlations indicate that the wasp may render the tick inhospitable to both pathogens. The presence of the wasp may have reduced risk of human infection on the island by either pathogen by as much as a third.     

The influence of leaf‐atmosphere NH3(g) exchange on the isotopic composition of nitrogen in plants and the atmosphere

The distribution of nitrogen isotopes in the biosphere has the potential to offer insights into the past, present and future of the nitrogen cycle, but it is challenging to unravel the processes controlling patterns of mixing and fractionation. We present a mathematical model describing a previously overlooked process: nitrogen isotope fractionation during leaf‐atmosphere NH_3(g) exchange. The model predicts that when leaf‐atmosphere exchange of NH_3(g) occurs in a closed system, the atmospheric reservoir of NH_3(g) equilibrates at a concentration equal to the ammonia compensation point and an isotopic composition 8.1‰ lighter than nitrogen in protein. In an open system, when atmospheric concentrations of NH_3(g) fall below or rise above the compensation point, protein can be isotopically enriched by net efflux of NH_3(g) or depleted by net uptake. Comparison of model output with existing measurements in the literature suggests that this process contributes to variation in the isotopic composition of nitrogen in plants as well as NH_3(g) in the atmosphere, and should be considered in future analyses of nitrogen isotope circulation. The matrix‐based modelling approach that is introduced may be useful for quantifying isotope dynamics in other complex systems that can be described by first‐order kinetics.