Substrate Contact,Mucus, and Eugregregarine Gliding1

ABSTRACT. Experiments have been carried out on Gregarina garnhami to examine some of the factors that may be significant in gliding. Suspension of gregannes in Ficoll showed that substrate contact is essential. Reflection interference microscopy shows that there are fluctuating surface/substrate contacts, but it is not necessary for the whole of the undersurface of the cell to be in close contact with the substrate. Gliding is always accompanied by the formation of a mucus trail. The effects of the drugs amphetamine and ephedrine on mucus trail formation and gliding have been examined. Lateral undulations of the epicyte folds have previously been implicated in grcgarinc gliding, but G. garnhami does not exhibit lateral undulations of the epicyte folds as it moves. The folds are predominantly straight with indications of varicosities or swellings along the length of the folds. These observations are discussed in relation to gliding movement.     

Analysis of Form and Function in Fossils

SYNOPSIS. Paleontology and the fossil record contribute an historicalperspective on the form-function relationship that is essentialto an understanding of the particular range of biological formsand functions that exist in the living world. The record containsrich evidence of forms and functions that do not exist in themodern world and provides a context for exploring arenas oftheoretical possibility and impossibility for organisms. Althoughthe basic data of the fossil record are static forms and patternsin the rocks, paleontologists have developed methods of inferringfunction. Analogy is the most important source of hypothesesfor the function of extinct organisms and enigmatic structures.Paleontological analogy frequently extends beyond biologicalform and structure to engineering solutions in familiar simplemachines and a variety of other human artifacts. Three tools have proved especially useful in the analysis andinterpretation of form in fossils. The paradigm method is auseful procedure for rigorous evaluation of alternative functionalpossibilities for enigmatic structures in a predominantly adaptivecontext. Constructional morphology reaches beyond the adaptivecontext to provide a conceptual framework for understandingthe full range of factors that contribute to organic form. Theoreticalmorphology provides the basis for examining the range of formsand functions that have actually evolved against possible morphologicaland functional space. This essay is structured to provide applicationsof these paleontological tools and to encourage incorporationof paleontological data and perspective into instruction inintroductory biology courses.     

A study of glands on cotton responsible for the high pH and cation concentration of the leaf surface

Groups of hygroscopic microcrystalline particles were found on the leaf surface of cotton, Gossypium hirsutum and were shown to be produced by glands in the epidermis. The glands were hydathode-like, about 20 μm in diameter by 25 μm long, with swollen, rounded, apices. They secreted high concentrations of magnesium and potassium and some sulphur and calcium, as indicated by X-ray microanalysis, onto the leaf surface. The proportions of elements present in gland secretions could be altered by changing the root environment of the plant. When the microcrystalline particles were removed and made up in distilled water the resulting solution had a pH of 10.2. It was established that the glands are responsible for the high pH and cation concentrations on the cotton leaf surface. The morphology and structure of the glands was investigated by light and electron microscopy and their possible function is discussed.     

Overwintering problems of newly established Miscanthus plantations can be overcome by identifying genotypes with improved rhizome cold tolerance

Miscanthus , a perennial rhizomatous C₄ grass, is a potential biomass crop in Europe, mainly because of its high yield potential and low demand for inputs. However, until recently only a single clone, M. × giganteus , was available for the extensive field trials performed across Europe and this showed poor overwintering in the first year after planting at some locations in Northern Europe. Therefore, field trials with five Miscanthus genotypes, including two acquisitions of Miscanthus × giganteus , one of M. sacchariflorus and two hybrids of M. sinensis were planted in early summer 1997 at four sites, in Sweden, Denmark, England and Germany. The field trials showed that better overwintering of newly established plants at a site was not apparently connected with size or early senescence. An artificial freezing test with rhizomes removed from the field in January 1998 showed that the lethal temperature at which 50% were killed (LT₅₀) for M. × giganteus and M. sacchariflorus genotypes was −3.4 °C. However, LT₅₀ in one of the M. sinensis hybrid genotypes tested was −6.5 °C and this genotype had the highest survival rates in the field in Sweden and Denmark. Although the carbohydrate content of rhizomes, osmotic potential of cell sap and mineral composition were not found to explain differences in frost tolerance adequately, moisture contents correlated with frost hardiness (LT₅₀) in most cases. The results obtained form a basis for identifying suitable Miscanthus genotypes for biomass production in the differing climatic regions of Europe.