Water impermeable seed dormancy

Viable seeds that do not imbibe water and thus fail to germinate in an apparently favorable environment are commonly termed impermeable or hard seed. This physical, exogenous dormancy is especially common in species of the Fabaceae. The ecological significance of hard seed includes the ability to rapidly recolonize burnt areas after fire and to withstand ingestion by animals and birds. Advantages and problems that hard seed cause in agriculture are discussed. Species from different families with impermeable seeds appear to have in common a layer of macrosclerid cells that form a palisade layer in the testa. The term strophiole and its contradictory use in botanical literature are discussed. Genetic factors and environmental conditions both affect the proportion of impermeable seeds produced. Methods of artificially softening impermeable seeds include acid and solvent, soaking, mechanical scarification, pressure, percussion, freezing, heating, and radiation treatments that can result in a change in germination from less than 20% in some untreated species up to 90% or more in treated species. Natural softening involves high temperatures and temperature fluctuations and the degree of desiccation of the seed. The mechanism of water impermeability is related to the testa and is thought to involve waterproofing substances including wax, lignin, tannin, suberin, pectin, and quinone derivatives. The hilum acts as a hygroscopic valve that prevents water uptake but allows water loss to occur at low relative humidities in some species. The strophiole is an area of weakness in the testa of some Papilionoideae while the chalaza region has been determined as an area of weakness inPisum andGossypium. The water impermeable status of some species is reversible at a seed moisture content greater than 10%. The hard seed of a species can be described both in terms of the amount and the degree of impermeability.     

Réflexions critiques sur l'écologieet la systématique des Lingules actuelles et fossiles

New topics on ecology and systematics of recent and fossil Lingulids lead to an obvious revision of our knowledges on this zoological group. At first, the recent species need systematics and taxonomy on the bases of new described specific criteria (as, morphology of deltidial areas, muscle disposition); the results are briefly indicated. But, in fossil species, disorder and disparity of used characteristics are emphasized.The general conceiving on ecology of Lingulids are reviewed and discussed, especially on bathymetry and salinity; sediment and oxygenation conditions; taphocoenosis and lingulid «communities. On recent species, all these points are also studied, especially some ecological requirements (salinity, bathymetry, grain size), and mechanism of burrowing ability, burrow living positions in the sediments, as shell preservations after death and fossilization, to facilitate the paleobiotope interpretations. Recent animals are euryhalin, surviving at salinities from about 13 to 42‰; they could be considered as well adapted to waters with strong salinity fluctuations. They show preference to fine sand bottoms (lowest particle size about 40–60 μm). Their bathymetric distribution occurs between 0 and about 500 m (Lingula especially between 5–50 m; Glottidia 15–70 m). The isotherms 8–10°C seem to restrict their geographical and bathymetric distribution.Therefore, some post-palaeozoic lingulid bedsare studied or redescribed on the bases of the above discussed characteristics, and new interpretations on the environmental situation are given (Trias of Vosges Mountains; Oligocene from Japan; Eocene of London Basin). More caution must be used in study of fossil Lingulids that are not especially animals living in infralittoral bottoms with low salinity and deficient oxygenation, as generally accepted.     

Amphetamine-induced release of dopamine from the substantia nigra in vitro

Incubation of chopped tissue from the substantia nigra of the rat brain with d-amphetamine resulted in a significant release of [³H]dopamine into the incubation medium. This effect was observed with both exogenous [³H]dopamine previously taken up by the tissue and [³H]dopamine endogenously synthesized from L-[3,5-³H]tyrosine. The observed release was greater in magnitude when the apparent conversion of released dopamine to 3-methoxytyramine was taken into account. The relevance of the present results to the previously postulated self-inhibition by dopaminergic neurons of the substantia nigra pars compacta is discussed. The present data also provide support for the concept that catechol-O-methyltransferase (E.C.2.1.1.6.) is located primarily extraneuronally in brain.     

In vivo inhibition of cholesterol uptake in rabbit aortas by 7-ketocholesterol.

The iv injection of 7-ketocholesterol into rabbits, made soluble by combining with bile salts, inhibited cholesterol uptake by the aorta. However, the inhibition was not as marked or as uniform as previously demonstrated in in vitro experiments. This difference may have been the result of lower plasma concentrations of 7-ketocholesterol in the injected animals. Gastric feeding of 7-ketocholesterol failed to inhibit aortic cholesterol uptake, probably because of inadequate plasma concentrations of the inhibitory steroid. The results suggest that the mechanism of 7-ketocholesterol on aortic cholesterol uptake is through competitive inhibition.     

An auto-anti-b in an a1b person. Serological studies.

The serum of a patient (Mr. Lat) with the regular blood group A1 B contains an anti-B reacting with all cells having a B antigen except Bx and cis AB. The anti-B reacts at 4 degrees C and occasionally at room temperature as shown by agglutination, absorption-eluction and by thermo-dynamic assays. The antibody is regarded as an irregular autoantibody belonging to the group of the so called "suppressed" or "latent" antibodies.     

DEVELOPMENT AND ORGANIZATION OF THE SECONDARY VESSEL SYSTEM IN POPULUS GRANDIDENTATA

The apical 22 cm of a dormant, first-year sprout of Populus grandidentata was sectioned serially, and the primary and secondary xylem systems were studied microscopically and graphically reconstructed. A total of 15 nodes was present on the mature stem and 14 foliar primordia in the dormant bud. The vascular traces in the lower portion of the mature stem conformed to a 2/5 phyllotaxy while those of the upper portion and within the dormant bud conformed to a 3/8 phyllotaxy. The 2/5 to 3/8 phyllotactic transition occurred in an extremely precise and systematic two-step pattern: (1) The lateral traces shifted to a new point of origin on the parent central trace, and (2) three new central traces were initiated in sequence by divergences from left-traces. Metaxylem, when followed downward, conformed to the arrangement of the procambial trace system only within one orthostichy. Below this point, the metaxylem components of lateral traces physically separated from those of the protoxylem and continued downward on a new course. Metaxylem vessels produced by the trace cambium originated from a postulated vessel-generating center at the stem-petiole junction. Each metaxylem vessel developing basipetally through the primary body was continuous with a secondary vessel developing basipetally in the secondary body. Because secondary development closed the vascular cylinder, vessels originating from developing leaves or primordia situated at higher levels in the shoot were displaced radially outward when they entered the secondary xyelm. The distribution of vessels in the secondary xylem can therefore be accounted for by a knowledge of the production and distribution of metaxylem vessels in the primary body.     

Étude des variations du nombre et de la répartition des muscles longitudinaux chez Phoronis psammophila Cori

In 21 samples, staggered over 18 months, 1725 composite muscle formulae have been established for Phoronis psammophila Cori. The study of variations of the number and distribution of longitudinal muscle bundles demonstrates the increase of the muscle number (3 or 4) with the age of the animals. This increase is displayed with difficulty because of the interactions of many phenomena, especially reproduction and so statistical tests have not indicated significance. The general and especially mean formulae of different samples do not indicate the increase of the number of muscle bundles with time, as proposed by Emig.