Re-dating the Early Upper Paleolithic Levels of Le Trou Magrite (Pont-à-Lesse,Belgium)

All but one of the published radiocarbon dates from the 1991–1992 excavations of Strata 3 and 2 at le Trou Magrite are considered too recent because the dating was done with then-standard chemical pretreatment protocols. This study re-dates Stratum 2 using the same, then-pioneering, XAD-2 purification method on bone collagen as had been used for the 44,650 cal BP date from Stratum 3. The results are two averaged dates that are in stratigraphic order between themselves and in relation to the Stratum 3 date: 43,400 and 43,500 cal BP, according to the IntCal20 curve. These dates are very similar to recently published dates for the earliest Aurignacian in SW Germany and the latest Neanderthal remains in Belgium and they are associated with artifact assemblages that, without obvious evidence of mixture (other than that which was highly localized), include Upper Paleolithic stone tools and blades/bladelets together with numerous sidescrapers, denticulates and notches which are not exclusively Mousterian artifacts. Nineteenth-century excavations in the cave of le Trou Magrite yielded unambiguously diagnostic Aurignacian artifacts and works of portable art that could conceivably have been from a deposit equivalent in age to these strata on the contiguous terrace. It is clear that the first blade(let)-rich assemblages in the site were created on the cusp of the transition from the Middle-to-Upper Paleolithic transition and replacement of the Neanderthals in NW Europe.     

Ultrastructure of meiosis in the hollyhock rust fungus,Puccinia malvacearum I. Prophase I — Prometaphase I

Summary A thoroughly documented account of the ultrastructure of the meiotic spindle pole body (SPB) cycle in a rust (Basidiomycota, Uredinales) is presented for the first time. The three-dimensional structure of the SPB and spindle during meiosis in the hollyhock rust fungusPuccinia malvacearum is analyzed from serial sections of preselected stages. This paper covers prophase I to prometaphase I. At late prophase I, the nucleolus disperses and does not reappear until the end of meiosis. The SPB at late prophase I consists of two, 4-layered discs, 0.8–1.0 m in diameter, connected by a middle piece (MP). The SPB is associated with a differentiated region of the nuclear envelope and nucleoplasm. At late diplotene to diakinesis, each disc generates a half spindle as it inserts into an otherwise intact nuclear envelope. The MP connecting the interdigitating half spindles elongates and eventually splits transversely during subsequent spindle elongation. Each half MP, which is attached to a SPB disc, becomes inserted in a sheath-like extension of the nuclear envelope. The intranuclear late prometaphase I spindle always becomes oriented perpendicularly to the longitudinal axis and sagittal plane of the metabasidium. There are 200–290 spindle microtubules (MTs) at each SPB at late prometaphase. The nonkinetochore MTs form a coherent central spindle around which the kinetochore MTs and bivalents are spread. A metaphase plate is absent. The results are compared with SPB behavior and spindle structure in early meiosis of other basidiomycetes and ascomycetes.     

Megaspore development in Selaginella. I. “Wicks”, their presence,ultrastructure, and presumed function

Summary Structures have been found in the locular space between the tapetal cells and megaspores in Selaginella argentea and S. kraussiana that enter the megaspore wall and extend to the plasma membrane of the megaspore cytoplasm. We have called these structures wicks. Unless special fixation procedures are used wicks are either very poorly preserved or not apparent. Wicks appear to be routes for the transport of materials from the tapetum to developing megaspores. The entry of the wicks into the megaspore wall and their passage throughout the wall implies that the megaspore wall of Selaginella is a three-dimensional mesh-work of inter-connecting spaces. Wicks have several macromolecular-sized subunits, and the results of our histochemical reactions indicated the presence of glycoprotein and/or mucopolysaccharide. X-ray microanalysis of the S. convoluta exospore showed that silicon is present in rod-shaped structures between units of the exospore in mature megaspores. Because of the size and form of the structures between the exospore units we consider that they are remnants of wicks stabilized by silicon.Present address:Cátedra de Palinologia, Museo de La Plata, Paseo del Bosque s/nro., 1900 La Plata, Argentina.