Interaction du photopériodisme et des effets de la zéatine, du saccharose et de ľeau dans la floraison du Chenopodium polyspermum

Interaction of photoperiodism and zeatin, sucrose and water effects on the flowering of Chenopodium polyspermum Root removal in Chenopodium polyspermum, a quatitative short-day plant, enhances flowering under non-inductive conditions. Presence of roots may be mimicked by zeatin applications on buds. Induction of flowering by short days may be counteracted by applications of zeatin, and appearance of flowers depends on the balance between number of inductive short days and zeatin quantity applied. Sucrose added in the culture medium or applied on buds acts as zeatin. Applications of water on buds may also delay flowering. These results show the plurifactorial regulation of the floral development of this plant. The relations between the non-specificity of the induction and the specificity of the morphogenetic response are discussed.     

Étude polarographique de la mobilisation du fer de la ferritine

Polarographic study of the mobilization of ferritin ironPolarographic study allows to propose a model for mobilization of ferritin iron: an equilibrium exists between iron core and small quantities of iron outside the protein.These iron atoms would be lying on electron acceptor sites including SH groups. The number of sites is dependent on iron content of ferritin.Therefore, the iron could be removed by the action of reducing agents such as xanthine oxidase or ascorbic acid, and then chelated by a complexing agent.     

Modulation de la Réponse du Xyléme selon la Nature de l'Agression Vasculaire

Modulation of the xylem response to different types of vascular aggressions The evolution of cells lining the vessels in the stem xylem of carnation was compared in sham-stressed (s. e.), V. dabliae-infected (i V. d.) and P. cinerescens-infected (i P. c.) plants. All experimental stresses triggered ultrastructural changes leading to the appearance of new cell types. In parallel, vacuolar polyphenols were metabolized and dense-core vesicles appeared. These were early and independant phenomena. In all cases the reactions of carnation xylem were stronger against Verticillium than against Phialophora. Differences in vascular gummosis were disclosed whatever the criterion used (speed of installation, relative importance of the phenomenon, level of structural complexity, dynamics of appearance of the different structures). The possible relations between cell structures and gummous secretions were investigated by means of comparison of an efficient defence system (i V. d.) with a deficient one (i P. c.). All the criteria selected for analysis confirm that faced with a specific parasite the host response was disrupted. In other words, the biosynthetic pathways normally used by the plant after a fungal aggression were blocked, slowed or diverted. The differences in the responses of carnation to Verticillium and Phialophora give a picture of parasite specificity in agreement with the model recently proposed by de Wit (1981) for tomato/Cladosporium fulvum.     

L'analogie et la représentation de l'art primitif à la fin du XIX siècle

In this paper, we will examine the foundations of Western representation of Paleolithic art at the end of the nineteenth century. Taking the period of 1864-1902 into account, we will prove the leading role of analogy between “modern primitive societies” and “prehistoric societies” in the very definition of “primitive art”. According to us, the representation of the “primitive artist” at that time was largely based in comparison between art which came from modern primitive societies living in Africa, Australia or America, and prehistoric art which was authenticated at about 1865. Through this examination, we will show the way in which analogy functions as a main category in the construction of scientific knowledge.     

Presence du Messinien dans la vallee du Rhone

According to the paleontological (molluscs and ostracods) and stratigraphical data, the Congeria rhodanicacclays are of Upper Messinian age. This oligohaline facies points out the local transgression of mediterranean origin in the Rhone basin, following a Lower Messinian erosive episode with coarse subaerial partial valley infill.     

Importance du sédiment dans la distribution des Lingules

Log-probability curves of grain-size distribution have been analysed of sediments collected in three previously described localities occupied by either Lingula anatina or L. reevei (Brachiopoda, Inarticulata). The grain-size population transported by saltation (average about 92–223 μm), generally associated with traction load population, determines Lingula distribution. The two preferential substrates of both studied species (density > 100 individuals/m^-2) are compact and stable sediments under moderate water currents: either coarse sands and gravels clogged by fine and very fine sands, or fine, very fine and clay sands (saltation populations more than 60%). As soon as the suspension population and/or traction increase in the sediment to the detriment of the saltation population, the density of Lingula decreases rapidly. Nevertheless, if grain-size distribution and populations have a primordial function for Lingula , other ecological features (i.e. the environmental fauna, high occurrence of digging species, the available nutrients) will affect the distribution and sometimes become prevailing. The absence of important changes in the shell shape of Lingula since its origin suggests that the grain-size requirements remained about the same.     

Utilisation des isotopes stables pour l’identification de l’origine du carbone dans la datation du charbon de bois du Paléolithique

Recent years have brought many results of radiocarbon dating the earliest periods of the Upper Palaeolithic that can bring light on the origins of figurative art by Sapiens or Neanderthals. These dates are often close to the limit of the field of radiocarbon dating; because they require measurements of the lowest amounts of radiocarbon, controls are particularly essential. Here we examine the case of the dating of charcoal, whose identification after decontamination is difficult. We suggest a method that does not require additional manipulation to determine whether carbon comes exclusively from charcoal: using the proportion of stable carbon isotopes 13C/12C which is often regarded as a signature (δ13C).     

Les Spatangus du Miocène et du Pliocène de l’Ouest de la France

Numerous fragments of spatangoid echinoids have been discovered in the Pliocene deposits of Challans, in Vendée (western France). In spite of the fragmentary data of the samples, a reconstitution of a complete test could be realized using the different fragments and their symetrization. The general shape of the test, and its architectural and ornemental characters allow establishing the presence of the genus Spatangus in western France during the end of Neogene. It allows to precise the biogeography of the genus Spatangus and of the morphological group S. (S.) purpureus on the Atlantic coast after the Messinian crisis. The Pliocene species is compared to the Miocene Spatangus (Phymapatagus) brittanus, abundant in Anjou, Brittany and Touraine. This older species was refered to the subgenus Phymapatagus according to the presumed lack of primary tubercles on its posterior interambulacrum. The discovery of well-preserved specimens, with primary tubercles on every parts of the test, in the Middle Miocene of Brittany allows to refute this subgeneric distinction and to refer the species brittanus to the subgenus Spatangus (Spatangus). The presence of this subgenus in western France is finally confirmed from Middle Miocene to Pliocene.     

Effet du refroidissement local de la tige sur le transport du AIA exogène en provenance du bourgeon apical et sur la croissance des bourgeons axillaires

Effect of local cooling of the stem on exogenous 1AA transport from the apical bud and on the growth rate of axillary buds .
Local cooling (1.5°C) of the stem (on 2 or 4 cm) of Vicia faba L. cv. Aguadulce for 15 h stops the exogenous IAA transport from the apical bud and causes a high accumulation of tracers above and at the level of the cooled zone. This clamping effect is reversed after removal of the cooling system. If the cooling system is maintained for 48 h, about 25% of the exported radioactivity passes the cooled zone. However, the percentage IAA transmitted decreases to about 6.6% if the cooled zone is sufficiently wide (4 cm) and the temperature lowered to 0.7°C±0.3°C. Using a cooling system of 4 cm (0.7±0.3°C) partially releases the lowermost axillary buds (ax₁ and ax₂) from apical dominance. Yet, the rate of growth of the axillary buds is generally lower than the growth rate after decapitation of the plant.     

Influence du substrat sur la répartition des Crustacés stygobies interstitiels du Haut-Atlas occidental

The interstitial stygobiont distributions of two rivers in the western High Atlas is analyzed in relation with sediment granulometry. Sixteen stations were sampled along the rivers N'Fis and Zat and their tributaries. Granulometry analyses were performed. Three grain size sediment types constitute the subterranean biotopes and reflect the local hydrodynamical conditions. The main rivers stations, which undergo frequent natural or human disturbances, are characterized by a high content of fine sediment; in contrast, tributaries stations show coarse and well-classified sediments due to more stable biotopes and more regular hydrological conditions. The 92 taxa group 28 stygobiontic species with 11 crustaceans species. PCA. based on 16 stations, three faunistic richness indexes and three granulometric factors display a high correlation between coarse grain-size content and the richness of stygobiontic taxa. A high silt content both limits the interstitial taxa and excludes crustaceans that occur only in coarse gravels. The granulometric preferenda in the species of the amphipod genus Metacrangonyx and isopods Microcerberus. Microcharon and Typhlocirolana are shown on Shepard triangular diagrams. Cohabitation of several species of the same genus could be explained by the occupancy of different ecological niches resulting from the grain-size proportion.     

Les statues-menhirs du Rouergue et du Haut-Languedoc : la posture des jambes et la technique de représentation des effigies féminines et masculines

Wex (1993) observes through the statuary of great historical cultures how body language appears to reflect the evolution of the respective status of man and woman. On the other hand, Serres (1997) reports that the feminine statues-menhirs of his so called groupe rouergat are represented with legs spread out, while masculine statues show broad as well as narrow postures. We examined this observation more systematically and further applied to it the properly ethological reading grid of Wex as a contribution to the history of gender relationships. A preliminary quantitative analysis aimed to determine which attributes give certainty about the sexual identity of the statues-menhirs. Special attention is given to the figures who underwent a gender change.