Mechanism of Pollination in Gladiolus: Roles of the Stigma and Pollen-tube Guide

Gladiolus has a dry type of stigma. Compatible pollen grainsalight and germinate on the receptive surface of the papillae,penetrate the cuticle and grow towards the style through a sub-cuticularpollen-tube guide of mucilage. This is secreted from epidermalcells of the stylodium and style canal. The cuticle, which coversthe pollen tube guide mucilage, is continuous through the stylecanal to the ovary. The wet stigma of Lilium also has cuticulartissue running through the style canal, covering the mucilage.     

Zoophycos size may indicate environmental gradients

Detailed examination through a continuous stratigraphic interval representing nearly the entire Lower Devonian Onesquethawan Stage shows that the presence and size of the trace fossil Zoophycos varies systematically throughout the unit. The lithofacies of this sequence are interpreted to represent a double offshore-nshore cycle. Both maximum and mean diameters of the Zoophycos web (=spreite) are relatively large within a more offshore setting and become progressively smaller towards both margins of this geographic (= stratigraphic) zone. Close inspection of Zoophycos morphology reveals a nearly perfect correlation (r = 0.96) between Zoophycos web diameter and meniscus height. Meniscus height bears a constant relationship to the maximum body diameter of the animal creating the burrow, consequently, size of the web is directly proportional to body size. Thus the animal is largest near the center of its environmental range and smallest near the margins. Other ichnofossils in the section ( Scalarituba, Phycodes, Chondrites ), measured on a more limited scale, show similar size variations with smaller forms at the margins of their respective ranges. Therefore, trace fossil size may be a sensitive indicator of paleoenvironmental gradients.     

Nitrogen and the koala (Phascolarctos cinereus): some indirect evidence

Indirect evidence provides additional support for the hypothesis that the level of available nitrogenous food is the major limiting influence in the abundance of the koala. It appears that koalas may select for low fibre content which is usually correlated with high nitrogen levels of leaves.     

Systematics, similarity and Acanthaceae pollen morphology

SCOTLAND, R. W., 1992. Systematics, similarity and Acanthaceae pollen morphology. A brief discussion of the history of Acanthaceae classifications is provided. It is argued that several approaches utilizing pollen morphological data for the classification of the family can be identified. The Lindau pollen types are shown to have an indirect relationship to Lindau's own classification. Pollen morphological similarity is explored within the context of cladistic methodology. It is shown that some of the Lindau pollen types are analogous. It is demonstrated that shared similarities can be of three types: conflicting (homoplasious), plesiomorphic and apomorphic.     

The RCE: a Riparian, Channel, and Environmental Inventory for small streams in the agricultural landscape

1. The Riparian, Channel and Environmental (RCE) Inventory has been developed to assess the physical and biological condition of small streams in the lowland, agricultural landscape. It consists of sixteen characteristics which define the structure of the riparian zone, stream channel morphology, and the biological condition in both habitats. 2. The inventory is based on the view that in landscapes where non-point source pollution and agriculture dominate, the environmental condition of small streams can be assessed by an appraisal of the physical condition of the riparian zone and stream channel. It is assumed that disturbance of this physical structure is a major cause for reduction of stream biological structure and function. This assumption is supported by a case study using fifteen Italian stream locations in which the RCE was found to be positively correlated to the benthic macroinvertebrate community as measured by the Extended Biotic Index (r = 0.80, P < 0.001) and the Shannon Diversity Index (r = 0.73; P < 0.001). 3. The inventory is designed for quick use to cover a large number of streams in a short period of time. When used it generates a numerical score which can be used to compare the physical and biological condition between different streams within a region. The numerical score is divided into five, colour-coded classes to facilitate use in streammonitoring programmes and to allow comparison with biological indices.     

Spatial and Temporal Variability during Periods of "Recovery" after Mass Bleaching on Western Atlantic Coral Reefs

Western Atlantic coral reefs were differentially affected bya mass bleaching (discoloration) event in 1987. We periodicallyassessed the "appearance" of zooxanthellate organisms betweenDecember 1987 and June 1988 at nine conspicuously affected sitesin the Bahamas, Florida, St. Croix, and Venezuela, using a standardizedpoint-count technique. Three to four months after the localinitiation of the event, the "bleached" state was still presentin one to three of the most abundant reef coral taxa and ina few of the less common species (n = 5 sites). "Recovery" occurredsomewhat faster at shallower depths, at least in the Bahamasand Florida. Scleractinian corals which were "prolonged bleachers"had foliaceous or massive, rather than branching, morphologies."Bleached" points disappeared from the point counts after $6to $8 months. Long-term field data on spatial and temporal variability inthe dynamics of zooxanthellate organisms would help us to understandthe ecological consequences of bleaching. More generally, weneed to distinguish anthropogenic changes in the structure andfunctioning of reef ecosystems from those which occur naturally.Point-count techniques are well suited for collaborative studiesinvolving rapid quantification of coloration states and healthin reef corals.     

The Effect of Specific Sterols on Cell Size and Fatty Acid Composition of Tetrahymena pyriformis W

The size and fatty acid composition of Tetrahymena pyriformis W cells were influenced by the provision of a nutritional supplement of ergosterol, cholesterol, or tetrahymanol, but not of 20-isocholesterol. Ergosterol and cholesterol addition led to a reduction in cellular volume, an increase in glycerophospholipid saturated fatty acid content, and an increase in palmitoleic acid and its metabolic products when compared to unsupplemented controls. Tetrahymanol supplementation resulted in an increase in cellular volume, a decrease in saturated fatty acid content, and a reduction in palmitoleic acid and derivatives. 20-Isocholesterol was accumulated by the cells; however, this compound had no effect on any of the parameters followed in this investigation and had only a small depressant effect on tetrahymanol biosynthesis. Ergosterol and cholesterol had the same impact on the ciliates, even though the ergosterol-supplemented cells contained approximately three times as much free sterol as did cholesterol-grown cells. The amount of the free cholesterol and metabolic products in supplemented cultures was similar to the amount of tetrahymanol present in control cultures. This observation suggests that the cells recognize qualitative differences among the various polycyclic alcohols rather than responding to the amount of sterol present. Increased cellular levels of tetrahymanol led to a response unlike that of the true sterols, which again suggests that the high degree of specificity depends on the structure of the added polycyclic alcohol. The changes in fatty acid composition may be required to maintain proper interaction of the polar lipids and the polycyclic alcohols to give an appropriate degree of membrane fluidity.     

Seed dispersal in a cycad,Macrozamia riedlei

The influence of animals on patterns of seed dispersal has not been well explored, despite the importance of seed dispersal in plant population biology. Furthermore, the exploitation of animals as dispersal agents has been considered one reason for the replacement of gymnosperms by angiosperms in the Cretaceous. We studied seed dispersal in a cycad, Macrozamia riedlei, and showed that in the absence of animals, ripe seeds drop directly beneath the parent not more than 40 cm from the base. Several animals eat the fleshy outer integument of the seeds, and possums (Trichosurus vulpecula), transport seeds up to 24 m from the parent. The postdispersal positioning of seeds gave a log density-log distance relationship of y = 7.20 – 2.85x (r²= 0.96, N = 17). Effective local dispersal may have contributed to the persistence of cycads in the world flora for the last 200 million years.     

Genetic differentiation in the molluscan species Littorina rudis and Littorina arcana (Prosobranchia: Littorinidae)

Six populations of Littorina rudis and ihree of L. arcana were screened for elcctrophorctically dctci table variation at 21 enzyme loci. These species reproduce by ovoviviparity and oviparily respectively, and both are members of the L. saxatilis species complex. The mean coefficient of genetic identity between the two species was high (0.957) and no diagnostic loci were observed. Allele frequency differences are maintained in sympatric populations of the two species. Intraspecific values of/ ranged from 0.944 to 0.995 and both species showed marked inter-population genetic heterogeneity, a feature consistent with their limited powers of dispersal. Heterozygosity is high in all populations of both species. Populations of I. rudis have higher mean heterozygosities (= 0.153) then L. arcane ( H = 0.132).     

Electrical Events Correlated with Contractile Vacuole Activity in the Suctorian, Heliophrya

SYNOPSIS. The surface membrane potentials of suctorian genus Heliophrya were studied with intracellular electrodes. Resting membrane potentials averaged -32 mV, and spontaneous depolarizing potentials occurring at apparently random intervals and having a variety of waveforms were routinely observed. Such spontaneous potentials were correlated in time with visually monitored contractile vacuole activity. Individual contractile vacuoles had unique, although somewhat variable, electrical signatures. In the presence of an intracellular electrode all vacuoles contracted independently, but at approximately the same frequency. The amplitude of the electrical potentials increased when the membrane was hyperpolarized and decreased when it was depolarized. The sign of such potentials reversed at between -10 mV and the zero membrane potential. A 20% decrease in the membrane resistance was measured at the peak of the spontaneous depolarizing potentials.