Establishment and development of patch reefs in the intracratonic Ordovician sequence near Chicoutimi, Quebec

Patch reefs occur near the top of the transgressive sequence of Ordovician Trenton Group limestones in the Chicoutimi area of Quebec, eastern Canada. Despite their small sue, these reefs comprise diverse assemblages dominated by bryozoans, corals, stromatoporoids and receptaculitid algae. Pelmatozoans and gastropods are also conspicuous. The reefs were initiated and grew in a fully marine, open shelf setting. Available substrates varied from loose skeletal lenses to soft, firm or hardened bioturbated wackestones, and the earliest stages of reef growth reflect this heterogeneity. Loose or less firm substrates were colonised by bryozoans and pelmatozoans and/or by receptaculitids, which, together with accessory organisms, stabilised the sediments and provided the basis for further reef development. The resultant firmer, slightly elevated substrates provided sites for attachment of stromatoporoids and colonial corals which spread over earlier reef organisms and sediments and dominated the later stages of reef growth. On hardened areas of sediment, stromatoporoids and corals colonised the surface directly and the early stabilising stage of reef growth is absent. The compositions and developmental stages of these Trenton Group reefs are comparable with those seen in broadly contemporaneous and often larger reefs elsewhere, and are among the earliest in which corals played an important role.     

Sources of Inorganic Carbon Acquired through CAM in Littorella uniflora (L.) Aschers

Madsen, T. V. 1987. Sources of inorganic carbon acquired throughCAM in Littorella uniflora (L.) Aschers.—J. exp. Bot.38: 367–377. The CO₂ dynamics of the lacunal air and the relative contributionof external and internal CO₂ sources to dark CO₂ assimilationwas examined in the submerged aquatic CAM species Littorellauniflora (L.) Aschers. Refixation of internal CO₂, released by dark respiration, constitutedabout 30–35% of the total dark CO₂ assimilation. At aCO₂ concentration of 0·2 mol m^–3 around the leavesthe external CO₂ uptake through the roots increased from 45%of the total CO₂ uptake at 0·7 mol m^–3 CO₂ to 100%at 1·6 mol m^–3 and 3·1 mol m^–3 CO₂around the roots. The negligible importance of leaf CO₂ uptakeat high CO₂ concentrations around the roots was the result ofa causative high CO₂ concentration in the leaf lacunae. The CO₂ permeability of Littorella leaves was high relativeto root permeability. This has at least two ecological implications:(1) it enhances the potential diffusive release of CO₂ fromthe sediment C0₂-pool via the lacunal system of the plants.This loss of CO₂, however, was found to be greatly reduced byCAM activity of the plants. (2) The high permeability of theleaf surface to CO₂ exchange allows the plants to assimilateCO₂ from the water surrounding the leaves when the concentrationis high, i.e. during extensive epiphyte dark respiration. Thus,CAM tends to facilitate retension of a high CO₂ pool in thesediment-plant system and at the same time allows the plantsto exploit the water column CO₂ source when it is abundant.This result is in accordance with the general idea that CAMin aquatics constitute a carbon conserving mechanism. Key words: Aquatic macrophytes, dark CO₂ assimilation, inorganic carbon sources     

The stem of Pachypteris papillosa (Thomas & Bose) Harris

Pachypteris papulosa (Thomas & Bose) Harris, leaves of a pteridosperm, are locally abundant in the Middle Jurassic of Yorkshire. Microsporophylls too are known but the stem has been represented only by a few puzzling fragments. Better-preserved stem material is now described. When young the stems were thick (up to 15 mm) and largely composed of soft parenchyma and thus succulent. The leaves are borne sparsely, each at the end of a prominent mamilla. The stem surface is covered by hemispherical emergences with a thickly cutinized epidermis which, when isolated, are beret-shaped. This cuticle is the only robust part of the young stem.
Later the stem formed a thick cylinder of wood and the surface was stretched. A new surface i presumed to be cork), was formed and the 'berets' and mamillac were lost. Branching occurs at distant intervals, when the stem divides nearly equally into widely diverging parts.
Pachypteris papillosa is pictured as a large shrub forming a mangrove-like thicket along tidal rivers.     

Time course of uptake of 14C-abscisic acid by Lemna gibba in relation to growth

The time course of growth of Lemna gibba L. in low concentrations of abscisic acid (ABA) and of uptake of ¹⁴C-labelled ABA into the plants was followed for up to 15 days. Fresh weight increase was arrested when the plants were transferred to ABA solutions. This inhibition was greatest during the first days after which a marked recovery took place. Dry matter production was only slightly affected by ABA. On a culture basis, the uptake of ABA was almost linear with time during the experimental period. The rate of uptake on a fresh weight basis was highest during the first two days but decreased rapidly from the third day. Most of the applied ¹⁴C remained in the culture solution throughout the experiments. Plants transferred to a solution without ABA retained most of their accumulated ¹⁴C. Possible explanations for the decrease in rate of ABA uptake and restoration of growth are discussed.     

The minute books of the Linnean Club, from 1811 to 1955

Sometime during the early spring of 1970 I was asked to write an account of our old minute books and was given a large box containing many books and sundry papers. All the old books were there and in good condition, except the first–1811 to 1815. So I wrote a report lamenting the absence of this book, but afterwards it turned up. It had never been lost, but being rather different from all the others it was not recognized. I now think this was rather fortunate, for the first book which is the most interesting, deserves ampler treatment. My report is kept strictly on the books, and only very occasionally have I drawn on information from the Society's records, or from the introduction to the list of the Club compiled by H. W. Monckton in 1922, using the Society's records.     

Studies on Auxin Protectors X. Protector Levels and Lignification in Sunflower Crown Gall Tissue

The lignification and differentiation of phloem fibers in sunflower stems is inhibited by growing crown gall tumors. Crown gall tumor tissue has previously been shown to contain large quantities of auxin protectors. Since auxin protectors are antioxidants which inhibit peroxidase-catalyzed reactions, and since the formation of lignin is known to involve a peroxidase-catalyzed reaction, an investigation was undertaken to examine the relationship between auxin protectors and lignification in sunflower crown gall tissue. Sunflower crown gall tissue placed into media low in mineral content, rapidly lignifies. In the low mineral media, protectors appear in the medium within an hour or two, implying that endogenously-synthesized protectors rapidly leak out of the tissue. In control media, the tissue neither lignified appreciably, nor did it exhibit an excessive amount of protector release. The addition of Ca²⁺ to the low mineral medium markedly slowed, but did not entirely prevent lignification; similarly Ca²⁺ markedly slowed the release of protector into the low mineral medium. Auxin protectors added to the low mineral medium did not inhibit lignification apparently because, in the medium, the protectors are rapidly oxidized to quinones. The addition of catechol, a substance which mimics protector, also failed to inhibit lignification and also formed a colored compound in the medium suggesting o-qui none formation. In contrast, dithiothreitol, a strong anti-oxidant which upon oxidation does not form a strong oxidant (such as o-quinone), when added to the low mineral medium does inhibit lignification. It is suggested that in the in vitro situation lignification and senescence occurs in low mineral media because the protectors leak out rapidly causing the cell's metabolism to favor peroxidase-catalyzed oxidations including those leading to lignification, while in the in vivo situation the excess protectors produced by crown gall tumor tissue diffuse into surrounding tissue, maintaining a reduced state in such tissues and thereby inhibiting differentiation and lignification. The synthesis of large quantities of protectors by the tumor tissue therefore could account for the anaplasia of the bundle caps observed in sunflower internodes in the vicinity of growing crown gall tumors.     

Endosymbiotic Methanogenic Bacteria In Anaerobic Ciliates: Significance For the Growth Efficiency of the Host

ABSTRACT Endosymbiotic methanogenic bacteria of three species of anaerobic ciliates (Plagiopyla frontata, Metopus conforms , and M. palaeformis) were inactivated with the specific methanogen inhibitor 2-bromoethanesulfonic acid. the absence of endosymbiont methanogens reduced growth rate and growth yield by about 30% in P. frontata and M. contortus , while no significant change in fitness was observed in M. palaeformis. In Plagiopyla the growth rate constant is not affected by an artificially increased pH₂ neither in normal nor in methanogen-free ciliates. the energetic advantage conferred by endosymbiont methanogens in Plagiopyla and in Metopus contortus probably is due to excretion of organic material from the bacteria at the expense of bacterial reproduction. It is unlikely that the maintenance of a low pH₂ within the cells due to H₂-consumption by the bacteria is important to the ciliates.     

The cost of ant attendance and melezitose secretion in the black bean aphid Aphis fabae

1. The aphid Aphis fabae (Scopoli) is facultatively tended by Lasius niger (Linnaeus) ants. Previously, we found that A. fabae colonies can be made up of several clones, and that clones display significant differences in the composition of their honeydew sugars, especially in the amount of the ant attractant sugar melezitose that they produce. 2. These clonal differences could greatly impact the strength of the mutualistic interaction with ants as well as the aphids' fitness. 3. Hence, the aim of this study was to compare the fitness of different A. fabae clones that differed in their melezitose secretion, and whether or not they were tended by ants. 4. Individual fitness indices, colony growth, and alate production of single‐clone aphid colonies were analysed. 5. The results demonstrate that the fitness consequences of ant attendance critically depend on an interaction between levels of melezitose production. In particular, we show that high‐melezitose secreting clones produce fewer alates and hence might have a lower dispersal ability in the presence of ants. 6. Furthermore, these data confirm previous evidence that ant attendance is costly and results in the production of fewer apterae.