Water relations of the canopy species in a Banksia woodland,Swan Coastal Plain,Western Australia

Abstract Diurnal and seasonal water relations were measured in selected species of a Banksia woodland at a site with groundwater at a depth of 6–7 m. The canopy co-dominants Banksia attenuata and Banksia menziesii exhibited similar patterns of variation in water relations, both diurnally and seasonally. Stomatal conductance was usually 0.4–0.5 cm s^?1 diurnally and seasonally and, generally, did not respond to water deficit and other factors. Transpiration was correlated positively with factors indicative of atmospheric evaporative demand, especially total global radiation and pan evaporation, and was highest in summer when canopy water use reached 2.1 mm d^?1. Xylem pressure potential at dawn averaged ?0.25 MPa in both species throughout the year. Minimum xylem pressure potential varied seasonally and was negatively correlated with transpiration. Seasonal means of minimum xylem pressure potential varied from ?1.0 MPa in winter to ?1.5 MPa in early summer. Both Banksia species appeared to function as phreatophytes, utilizing groundwater which enabled them to maintain high rates of water use in late summer. Water use over a 12 month period totalled 635 mm, of which the canopy and understorey contributed 61% and 39%, respectively. Water use in the woodland was dominated by the canopy in late summer and the understorey at other times.     

Megasporogenesis and the Subsequent Cell Lineage Within the Ovule of Taxus baccata L.

Megasporogenesis in Taxus led to a T-shaped tetrad, the mitochondriaand plastids being largely confined to the chalazal megaspore,the only spore to show further development. Germination of themegaspore followed very soon after its formation. The femalegametophyte was initially coenocytic but after about one monthit became cellular, new walls arising between the nuclei inpositions marked out by accumulations of cisternae of endoplasmicreticulum. No ‘secondary spindles’ or other formsof microtubular participation in the siting of these walls couldbe detected. The development of the archegonia could not be resolved withcertainty, but it seemed likely that the cell analogous to thecentral cell of the pteridophyte archegonium eventually becamethe egg cell. The cytoplasm of the egg cell was clearly zoned.Prominent in the outer cytoplasm were granular bodies, 2–5µm in diameter, identifiable with the ‘grandes inclusions’described from the egg cells of conifers. The evidence pointedto their being derived from hypertrophied plastids which hadencapsulated part of the cytoplasm, a view strengthened by thecomplete absence of recognizable plastids from the mature cell.Bundles of microtubules radiating from the nuclear envelopewere a conspicuous feature, possibly stabilizing the zonationof the cytoplasm. Megasporogenesis, Taxus baccata, egg cell, ‘grandes inclusions’     

Microreticulation in Cambrian Ostracoda and its relation to similar patterns in tertiary and Recent Ostracoda

The Cambrian bradoriid ? Parahoulongdongella sp. is shown to have a microreticulate (2nd order) surface sculpture. A possible organic sheet‐like origin is proposed for this reticulation. The relation between this second order pattern and those found in tertiary to Recent Ostracoda is discussed.     

The Vascular Pattern of a Rhizomatous Ginger (Alpinia speciosa L. Zingiberaceae). 2. The Rhizome

The vascular system in the underground rhizome of Alpinia speciosaL. (Zingiberaceae) is seen to be arranged in three distinctzones. (1) An inner system of ‘scattered’ vascularbundles which serial cinematography reveals to have an axialpattern conforming to the basic ‘palm’ configuration(a system of upwardly branching leaf traces with interconnections).(2) An intermediate zone comprising a thin perforated cylinderof anastomosing vascular strands having direct contact withboth roots and inner system bundles. (3) An outer system offreely-anastomosing vascular bundles. Connexion of outer andinner system occurs in the form of extensive bridging from innersystem leaf traces as they depart obliquely between the outersystem network. The interrelation of the three systems, plus root and branchinsertion, is illustrated by means of diagrammatic three-dimensionalreconstructions. The intermediate zone is intimately associatedwith root insertions and with the inner system, and is shownto obliviate potential bottlenecks at the point of lateral branchinsertion in this sympodial rhizome system. A comparison ismade with other monocotyle-donous vascular systems. Alpinia speciosa L., shell ginger, rhizome, vascular anatomy     

White Ethnogenesis and Gradual Capitalism: Perspectives from Colonial Archaeological Sites in the Chesapeake

The piecemeal development of capitalist socioeconomic systems in the colonial Chesapeake was deeply intertwined with projects of white ethnogenesis. Crafting a sense of "groupness" along lines perceived as racial required free "whites" to remain economically and socially interdependent. A variety of strategies and material forms—including reciprocal exchanges, hall-parlor house plans, and earthfast construction—facilitated this cohesion. Such integrative tactics coexisted in colonists' behavioral repertoires with more "capitalistic" strategies that prioritized private profit over social obligation. Colonists' deployment of diverse social strategies reflects a complex calculus assessing the benefits of economic autonomy against the benefits of ethnic ("white") solidarity. These dynamics can be illustrated through an 18th-century archaeological site at Flowerdew Hundred in the Chesapeake.     

I-DNA suppressed by Ethidium Bromide and accumulated with Dactinomycin

THE I-DNA in cytoplasmic particles^1–4 of embryonic chick cells has a 260 nm/280 nm ratio of 1.95 (ref. 5) and a buoyant density of CsCl of 1.700–1.703 g/ml.; mitochondrial DNA has a buoyant density of 1.708 g/ml.^6,7. Other reports of non-mitochondrial cytoplasmic DNA different from nuclear DNA have appeared recently^8–10.     

Comparative seed germination ecology of Austrostipa compressa and Ehrharta calycina (Poaceae) in a Western Australian Banksia woodland

Austrostipa compressa, a native ephemeral of southwest Western Australia was stimulated to germinate under a range of temperatures, in the presence of light, and exposure to smoke-water. This combination of environmental cues results in winter-maximum germination in immediate postfire and disturbed-soil environments of this Mediterranean-type climate. In contrast, Ehrharta calycina, an introduced perennial grass from southern Africa that has invaded Banksia woodlands, germinated under a wide range of temperature and light conditions, but showed no promotive response to smoke-water. Although A. compressa seeds tolerated heat shock better than E. calycina, the self-burial mechanism of A. compressa seeds ensures protection from fire. High-intensity fire could have a greater impact on E. calycina, as the seeds of this species tend to accumulate in the top of the soil profile where they are more susceptible to high temperatures. Although seeds of E. calycina are more susceptible to high temperatures, survival of mature individuals by postfire resprouting ensures continued survival in native woodlands. Estimates of soil seed bank densities showed extreme variability, but some recently burnt areas of the Yule Brook Botany Reserve contained up to 8000 seed m^?2 of A. compressa and nearly 75 000 seeds m^?2 of E. calycina. Viable soil seed bank densities of A. compressa are reduced with time-since-last fire, but areas of greater than 45 years since the last fire, still contained up to 119 seeds m^?2. In both species, only about half their soil seed bank germinates following fire, thus ensuring the potential for later recruitment. Massive soil seed populations of E. calycina in native Banksia woodlands pose a major problem to management of this plant community type.     

Branch construction and bud defence status at the canopy surface of a West African rainforest

Branch specimens were collected from the very tops of tropical tree crowns in southern Cameroon, West Africa. An analysis of branching patterns revealed a consistency of form across unrelated taxa. All specimens showed evidence of rhythmic growth cither due to the regular occurrence of dormant terminal buds or due to sympodial growth with loss or flowering of terminal buds. Study of bud anatomy revealed an extensive array of protective devices associated with drought tolerance and herbivore defence. Normally a considerable excess of dormant, well protected axillary buds were present which (almost without exception) existed in a viable state. In very many instances the large dormant bud population was due to the presence of accessory buds, i.e. > 1 bud in the axil of each leaf. The microclimate at the outer surface of a tropical rainforest may experience a daily increase in temperature and associated depression in humidity; the canopy surface characteristics are more akin to chaparral shrub vegetation than to familiar rainforest understorey vegetation.