Effects of Population Density on Sex Expression in Onoclea sensibilis L. on Agar and Ashed Soil

Population density affected the sex expression of agar-growngametophytes of Onoclea sensibilis L. The time of onset of sexualitywas advanced, the proportion of females was increased, and thegrowth rate of individuals was greater at lower densities. Populationdensity had no effect on the sex expression of Onoclea grownon ashed soil, and there was no difference in growth rate ofindividuals grown on ashed soil at different densities. Covariateanalysis, using thallus width as a measure of growth rate, indicatedthat the effect of density on sex expression was mostly associatedwith growth rate. The differing effects of population densityon agar and ashed soil demonstrate that substrate influencessex expression in Onoclea. This influence is most dramatic insingle-gametophyte cultures, where agar cultures produced 97per cent females and ashed soil cultures 100 per cent males. Onoclea sensibilis L., sensitive fern, fern gametophytes, sexuality, population density     

Two New Menosporine Gregarines, Hoplorhynchus acanthatholius N. Sp. and Steganorhynchus dunwoodyi N. G., N. Sp. (Apicomplexa: Eugregarinorida: Actinocephalidae) from Coenagrionid Damselflies (Odonata: Zygoptera)

ABSTRACT. Hoplorhynchus acanthatholius , n. sp. is described from Enallagma civile , the Civil Bluet damselfly. Trophozoites are solitary, lie in the mesenteron between the peritrophic membrane and the epithelium, and attain a maximum length of 850 μm. Epimerite ovoid to broadly ovoid; anterior margin bearing eight equidistant retroarcuate hooks; attached to protomerite by means of a vermicular stalk. Protomerite ovoid; deutomerite narrowly obvoid. Gametocysts spherical; diam 300 μm, sporulating by simple dehiscence in 48–72 h. Oocysts are characteristic of Menosporinae: smooth, biconical, crcscentic, uniform in size and shape. Steganorhynchus dunwoodyi , n. g., n. sp. is described from the damselfly Ischnura verticalis. The genus is characterized by an epimerite comprising an ovoid papilla enclosed in a retractable, globular sheath, borne on a long vermicular stalk. Trophozoites are solitary, lie in the mesenteron between the peritrophic membrane and epithelium, and attain a maximum length of 605 μm. Protomerite very broadly ovoid; deutomerite obvoid. Gametocysts spherical; diam 258 μm, sporulating by simple dehiscence in 48–72 h. Oocysts are characteristic of Menosporinae: smooth, biconical, crescentic, uniform in size and shape. The population dynamics of H. acanthatholius and S. dunwoodyi among damselfly populations in five Nebraska localities are presented.     

Energy-Level Model for Isothermal Seed Germination

We have been successful in building an energy-level model thatdescribes seed germination. We used the autocatalytic reactionrate equation to fit the germination rate for seed germination.The two parameters [A]₀ and [F]₀ were found by fitting the integratedgermination rate equation to the data. The values of [A]₀ and[F]₀ obey the Arrhenius equation and give activation energiesfor the second and third stage of the four-compartmental modelof seed germination. The thermodynamics of isothermal seed germinationis proposed and the enthalpy, entropy, and free energy are calculatedfor the transition from state A to state F. The time delay isa function of temperature and it leads to a rate constant thatcan be used to get the activation energy for the total germinationprocess. We believe the model is universal. It fits alfalfa(Medicago sativa), turnip (Brassica rapa), and lettuce (Lactucasativa) seeds. Key words: Seed germination, thermodynamics, kinetics, Arrhenius, energy-level model     

Activation waves in a model of platelet aggregation: existence of solutions and stability of travelling fronts

Platelets cohere to one another to form platelet aggregates as part of the blood's clotting response. The ability of a platelet to participate in this process depends on its prior activation by chemicals released into the blood plasma by other activated platelets. We study the piecewise-linear system of reaction-diffusion equations which, in one spatial dimension, describe the chemically-mediated spread of platelet activation. We establish the existence of classical solutions to this system of equations, and show that these solutions do not blow up in finite time. We also explicitly construct travelling front solutions and discuss their stability. Finally, we present numerical evidence which suggests that for a broad range of initial data with the correct limiting values at ± , the solution to the initial value problem rapidly evolves into the travelling front solution provided the front is linearly stable.     

Immunoloealization of integrins in the normal and neoplastic colonic epithelium

Cryosections of normal colon (NC), tubular and villous adenomas (TA, VA), and variably differentiated colon adenocarcinomas (CA) were immunostained with monoclonal antibodies to α₁₋₆ and α_v, and β₁₋₄ integrin subunits; select samples were stained for cytokeratin (Ck) 20 and villin. In NC, α₂ staining was strongest in crypt cells; α_1,3 and α_v, and β_1,3 and β₄, and Ck 20 and villin predominated in superficial enterocytes. In TA and VA, monolayered glands showed integrin, Ck 20 and villin patterns that differed slightly from both crypt and superficial enterocytes. Complex glands in VA showed decreased integrin staining and basal polarization; Ck 20 and villin were strong only in luminal cells. CA showed overall weaker integrin staining than adenomas. Regardless of invasion depth, well formed malignant glands mimicked TA; pleomorphic glands mimicked VA with focal basal integrin polarization and solid clusters displayed scanty integrins, uneven Ck 20, and villin in occasional cells. Diverse integrins in crypt compared with superficial enterocytes reflect changing adhesive requirements as cells migrate and terminally differentiate. Decreasing expression and altered distribution of integrins, Ck 20 and villin noted in TA, VA, and in CA of increasing grade indicate that certain adhesive and cytoskeletal features more closely relate to glandular architecture than to depth of invasion.     

Axenic Cultivation of Trypanosomatids Found in Corn (Zea mays) and in Phytophagous Hemipterans (Leptoglossus zonatus Coreidae) and Their Experimental Transmission

ABSTRACT. Trypanosomatids isolated from corn seeds and from digestive tract and salivary glands of Leptoglossus zonatus (Hemiptera, Coreidae) were obtained in pure cultures. In experimental transmission, the flagellates present in naturally infected insects were able to infect laboratory-raised corn. A simplified liquid culture medium was established that increased parasite yield three- to five-fold. Cultured and cloned parasites, and forms found in insects and corn as well, were studied by light and electron microscopy. A remarkable finding was the observation that the cultured strain 163M bears a surface coat similar to that observed in naturally occurring African trypanosomes. but not observed in trypanosomes in vitro. Based on the biochemical characteristics of the arknine-ornithine cycle and on the presence of this cell coat, we propose that the strain 163M is a new species and name it Herpetomonas macgheei n. sp.     

The Neural Network of the Limulus Retina: From Computer to Behavior

SYNOPSIS. The visual system of the horseshoe crab, Limulus polyphemus,provides an excellent opportunity for studying the neural basisof behavior. Quantitative analysis of the animal's visual behavioris now possible as is theoretical analysis of information processingin its retina. We combine these theoretical and behavioral approachesto investigate the nature of the signals the eye transmits tothe brain for the animal to see. Over the years theoretical studies of the Limulus eye were restrictedby the limited capabilities of single processor digital computers.However, a breakthrough in technology with the advent of parallelcomputers greatly enhances the analysis of large neural networkssuch as that of the retina. We have developed a time-dependentmodel of the Limulus retina on the Connection Machine (ModelCM-2), which is a massively parallel computer containing 32,768processors. The model represents a matrix of 64 x 128 receptorsand simulates interactions among receptors with digital filtersand transduction and adaptation within a receptor by a multistagecascade. Neural response patterns computed with the ConnectionMachine model replicate to a first approximation the patternsof neural activity recorded in the laboratory. Behavioral studies of Limulus vision carried out in the fieldcan be simulated on the Connection Machine. Neural responsesrecorded from behaving animals serve to test the accuracy ofthe model. Thus far we have developed just one model of theretina, but it eventually will have two forms, "daytime" and"nighttime," to account for the known circadian rhythms in retinalfunction. With a combination of field, physiological, and theoreticalstudies, we hope to gain a better understanding of the neuralmechanisms that underlie the animal's visually-guided behavior.