Rates of Leaf and Tiller Production in Young Spaced Perennial Ryegrass Plants in Relation to Soil Temperature and Solar Radiation

In an experiment designed to investigate the rate of leaf appearanceand tiller production in young spaced plants of three clonesof perennial ryegrass grown in the field, it was found thatthe rate of leaf appearance per tiller increased linearly withmean soil temperature up to approx. 14 °C. The rate of productionof tillers in relation to the rate of leaf appearance (sitefilling) appeared to be virtually independent of weather conditions.In plants which were adequately established, but still relativelysmall, site filling was equal to or exceeded the theoreticalsteady state; all the tiller buds which were being formed weredeveloping into visible tillers. Thus the relative rate of tillerproduction was controlled by the rate of leaf appearance. Inlarger plants site filling was less complete, and site redundancieswere probably caused by within-plant competition for light atthe tiller bases. Lolium perenne L., perennial ryegrass, tillering, leaf production, solar radiation, soil temperature     

Paramecium sonneborni n. sp., a New Member of the Paramecium aurelia Species-Complex1

ABSTRACT. From an intermittent stream in College Station, Texas, a Paramecium was isolated that did not appear to belong to any recognized species. On the basis of nuclear and whole-body morphology, it can be assigned to the Paramecium aurelia species-complex, and it can be distinguished from other members of that complex on the basis of mating-type reactivity and isoenzyme patterns. These characteristics are felt sufficient to justify a new species assignment. The new species has been named Paramecium sonneborni n. sp. in honor of the late Dr. Tracy M. Sonneborn of Indiana University.     

Characterization of Plant Epidermal Lens Effects by a Surface Replica Technique

Optical replicas of leaf surfaces were made for characterizingthe lens properties of individual epidermal cells. Using a dentallatex, moulds were made of leaf surfaces and subsequently usedto produce agarose replicas. The replicas focused light in amanner similar to intact epidermal cells and it was possibleto measure both focal lengths and intensifications within leafreplicas of Thermopsis montana, Mahonia repens, and Smilacinastellata which had epidermal cells of different diameter. Focallengths ranged from 74—130 µm which indicated thatlight was concentrated within the underlying photosynthetictissues of these leaves. Focal intensifications were measuredsensiometrically and were 1.5 for T. montana and 2-6 for theother species. These values compare favourably with calculatedfocal lengths and measurements taken from isolated epidermallayers. The results indicate that the epidermis can concentratelight within the leaf to amounts well in excess of ambient light.Furthermore, the replicas faithfully reproduced fine anatomicaldetails from a wide variety of leaves and they provide a non-destructiveway to reproduce surface characteristics for anatomical andphysiological studies.     

Patch dynamics of the stream macrophyte, Callitriche cophocarpa

1. We examined changes in position and growth of Callitriche cophocarpa patches in a shallow section of a small Danish stream during the main expansion of plant cover between April and June. Mean upstream growth of patches was only 7.5% of downstream growth. The mean growth rate was 1,02cm day^?1 in length and 0.55 cm day^?1 in width and the growth rates were not significantly dependent on patch size. For patches with an area (A) above 100cm², the growth rates in patch area (dA/dt) was proportional to patch circumference and thus √Aand the relative growth rate (dA/dt A^?1) was inversely proportional to √A.The smallest patches (<100cm²), however, expanded less than expected because of their combined tendency to grow more slowly in patch length and width than larger patches. 2. The expansion of plant cover will be much more rapid in many medium-sized patches compared to few large patches of a similar combined area, because internal selflimitation by light and space is partially relieved in smaller patches. We anticipate that recruitment and mortality of new-formed patches are critical steps preceding areal expansion. Quantification of these processes are needed fully to evaluate patch dynamics and space occupation.     

Water and Solute Balance in the Transition to Land

Terrestrial crabs are physiologically rather similar to theiraquatic relatives, despite their markedly different access towater and ions. They have high evaporation rates and void vitalsalts in isosmotic urine. Some of them manage to have fairlymiserly water and ion budgets, but others succeed despite profligacy.There is no single solution to the challenges of terrestriallife; each pairing of animal and environment must be seen asa system in which a unique suite of behaviors compensates forlimited physiological prowess. By exploiting temporal and spatialvariability of available microhabitats, each species assemblesa "composite habitat" in which it can balance the "debit" sidesof its water and ion budgets with the requisite "credits."     

Inhibition of Nitrate Assimilation in Roots in the Presence of Ammonium: The Moderating Influence of Potassium

Experiments were conducted to investigate the effect of concentrationof NH₄⁺ in nutrient solution on root assimilation of NO₃^–and to determine whether the NH₄⁺NO₃^– interaction wasmodified in the presence of K⁺. Dark-grown, detopped corn seedlings(cv. Pioneer 3369A) were exposed for 8 h to 0.15 mM Ca(NO₃)₂and varying concentrations of (NH₄)₂SO₄ in the absence or presenceof 0.15 mM K₂SO₄. The accelerated phase of NO₃^– uptakeappeared most sensitive to restriction by additions of 0.15mM (NH₄)₂SO₄. In the absence of K⁺, the restriction increasedonly slightly even when solution (NH₄)₂SO₄, was increased from0.15 mM to 12.5 mM which was accompanied by an increase of NH₄⁺in the tissue from about 7.0 to 35 µmol g^–1 fr.wt. of root. Increasing concentrations of solution NH₄⁺ progressivelyinhibited net K+ uptake. At the highest solution NH₄⁺ concentrations,there was an initial net efflux of K⁺ and no net influx occurredduring the treatment period. The severity of the NH₄)SO₄ restrictionof NO₃^– uptake was moderated considerably in the presenceof K⁺ as long as a net influx of K⁺ occurred. However, net influxof K⁺ was not associated with alteration of NH₄⁺ uptake, assimilation,or accumulation in the root tissue. The lack of correlationbetween the severity of restriction of NO₃^– uptake andendogenous NHJ suggested the restriction resulted from an effectexerted by exogenous NH₄⁺ which tended to saturate at lowersolution NHJ concentrations or by inhibitory factors generatedduring assimilation of NH₄⁺. Several mechanisms were postulatedto account for the moderating influence of K⁺. In all experiments,root NO₃^– reduction was restricted by the presence ofambient NH₄⁺. The quantitative decreases in reduction tendedto be less than decreases in NO₃^– uptake and therefore,could result from inhibition solely of uptake with subsequentlimitation in availability of substrate for the reduction process,but the possibility of a direct effect on reduction could notbe excluded.     

A Note on Scanning Electron Microscopic Assessment of Stomacher Action on Chicken Skin

Scanning electron microscopy was used in conjunction with normal microbiological procedures to evaluate the stomacher as a means of recovering bacteria from chicken skin. Stomaching removed most bacteria from the skin and viable counts of skin micro-organisms obtained by this method were not significantly different from those obtained by blending. The stomacher represents a useful alternative to blending techniques commonly used to assess contamination of poultry carcasses.