摘要:

In dehisced anthers of allGymnocalyciumspecies (Cactaceae, subfam. Cactoideae, tribe Trichocereae) investigated so far, a small percentage of pollen grains are aggregated by only a few threads. These threads are located at the margin of the dehiscing zone of stomium and septum. They are not part of the pollen grain wall, and they are not resistant to acetolysis, thus indicating the absence of sporopollenin. The threads originate in part from modified stomium/septum cells (split cell walls, cytoplasmic remnants and lipid droplets) and in part from pollenkitt produced by the—now desintegrated—tapetal cells. This highly viscous, gum‐like substance along the modified stomium and septum cell walls may assume an irregular thread‐like habit before or during dehiscence. Pollen aggregates may be formed frequently by different sticky or non‐sticky agents. A detailed conspectus on origin, nature, significance and function of various types of pollen‐connecting agents forming threads is presented. Pollen‐connecting threads are normally efficient pollination vehicles and are restricted to flowers pollinated by large insects or vertebrates. The genusGymnocalyciumis probably exclusively bee‐pollinated, with most pollen connected by pollenkitt. The functional role of the threads inGymnocalyciumis uncertain: since only a few threads connect a small number of pollen grains per pollen‐sac, they hardly play a significant role in pollination ecology. The threads most probably represent a character restricted to the genusGymnocalyciumas they have not been observed in closely related genera.

ISSN:0017-3134    

DOI:10.1080/00173139709362583

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The pollen morphology of seven species ofEuphorbiasubg.Agalomasect.Tithymalopsis(Euphorbiaceae), and ten more species added by a later worker, has been examined with light and scanning electron microscopy. Three poorly differentiated exine sculpturing patterns have been observed within the 17 species. Species of sect.Tithymalopsisdo not have pollen that could be distinguished from pollen of the 10 related species of subg.Agaloma.The present results do not support the monophyly of sect.Tithymalopsisproposed by morphological and isozymic data.

ISSN:0017-3134    

DOI:10.1080/00173139709362584

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

In Cambro‐Ordovician transitional beds of the Hassi R'mel area, northwestern Algeria, three stratigraphically successive acritarch assemblage zones can be recognized: HM/A (uppermost Cambrian), HM/B (basal Tremadoc), and HM/C (lower Tremadoc; with associated graptolites of theRhabdinopora flabelliformissensu lato group). Thus, the boundary between assemblages HM/A and HM/B is considered to approximate to the Cambrian‐Ordovician boundary in the study area. Six morphologically distinctive acritarch species that facilitate recognition of zonal boundaries are described. One genus and four species are newly instituted:Phenacoon imperfectumgen. et sp. nov.,Impluviculus araneussp. nov.,Ladogella saharicasp. nov., andMultiplicisphaeridium attenuatumsp. nov. Revised circumscriptions of two other species—Acanthodiacrodium baculatumandBaltisphaeridium verutum—incorporate morphological details not previously available.P. imperfectumandL. saharicaare abundant at the top of assemblage zone HM/A;A. baculatumcharacterizes the base of assemblage zone HM/B; andB. verutum, I. araneusandM. attenuatumare characteristic components of the lower part of HM/C assemblage zone.

ISSN:0017-3134    

DOI:10.1080/00173139709362585

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Records of the start of Birch pollen seasons monitored at three sites in the UK for periods of up to forty two years indicate a recent trend for the pollen seasons to begin earlier. This trend shows a close relationship to an increase in cumulative temperatures in the months of January, February and March recorded near each of the sites during the study period.

ISSN:0017-3134    

DOI:10.1080/00173139709362586

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Since Switzerland has a complex topography with high mountains it was very uncertain how much and what kind of pollen can be found at high elevations. In order to study the content of air masses at high elevation a Burkard Seven Day Recording Volumetric Spore Trap was installed at the meteorological station at Gütsch (alt. 2300 m) in the Swiss Alps. Although there are no trees at all at this elevation it is amazing how much tree pollen is found. With the exception ofAlnus viridismost of this pollen is transported across the Alps. Special attention is given to the pollen ofCastaneawhich can serve as a real tracer, since this pollen originates exclusively from the southern part of Switzerland (Tessin). Grass pollen, on the other hand, has local sources, even at this elevation, once the snowy season has ended. Grass pollen and pollen of weeds, therefore, need not have been transported. The surprisingly high amount of pollen observed may also have a relevance for people with pollen sensitization because generally it is assumed that hayfever symptoms decrease quickly with increasing elevation.

ISSN:0017-3134    

DOI:10.1080/00173139709362587

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Intradiurnal fluctuations in the airborne pollen count of nine of the taxa which are most important in the atmosphere of Málaga (SE Spain) were studied. A mathematical formula, the “intradiurnal distribution index”; (IDI), permitted an accurate numerical comparison of the different years and taxa studied. Sampling was carried out during the period 1992–1995 with the aid of a Burkard volumetric spore trap. Although on the basis of the IDI values obtained, three types of behaviour were distinguished, most taxa showed maximum concentration peaks around midday.

ISSN:0017-3134    

DOI:10.1080/00173139709362588

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Although olive pollen is one of the most widespread aeroallergens in the Mediterranean area, very few studies present predictive models. We have already seen that in Málaga (Southern Spain) the meteorological variables which have the greatest influence on airborne pollen concentrations during the pre‐peak period are accumulated rainfall and mean temperatures from the chilling requirement for flowers buds initiation. This work presents the simple and multiple linear regressions obtained by using daily pollen concentrations as a dependent variable and the daily values of the above mentioned meteorological parameters as independent variables. When establishing an overall predictive model, we chose the equation of the simple linear regression pollen‐accumulated temperatures obtained during 1992–94 (y = 0.003x‐3.863) since this provided the greatest lineal fitting.

ISSN:0017-3134    

DOI:10.1080/00173139709362589

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A continuous aeropalynological survey of the atmosphere of Mar del Plata was carried out from December 1992 to November 1993 using a Burkard volumetric spore trap. Ten‐day averages were calculated for 28 relevant taxa, selected on the basis of their relative high concentration in the air. The total annual concentration (Cupressaceae pollen excluded) was 84,445 grains/m3, with 42% of total appearing during September and October. The pollen spectrum largely reflects urban anemopyilous vegetation, which is characterised by naturally occuring herbs and by ornamental shrub and tree species. A qualitative analysis shows two major pollen seasons related to the atmospheric dominance of either arboreal or non arboreal pollen.

ISSN:0017-3134    

DOI:10.1080/00173139709362590

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The effect of varying weather conditions on the hourly number of airborneCladosporiumconidia was studied in forest environments during three summers. All factors having diurnal periodicity correlated significantly with the number of spores. Because of the great variation in weather and the interaction of weather factors, the most important factors were not the same for each summer. Temperature was important in each year. Relative humidity was most important in the first rainy summer, and precipitation was more important during the two drier summers than in the first summer. The maximum spore counts were obtained at the onset of rain, indicating the effectiveness of the first rain drops in detaching conidia. The amount of water precipitated also promoted the production of conidia, since it correlated positively with the number of spores in the air several hours later. Spore detachment also seemed to be closely related to decreases in relative humidity and increases in wind velocity which occurred in the morning. An increase in wind velocity from 0.5–1.0 m−sincreased the number of spores most effectively.

ISSN:0017-3134    

DOI:10.1080/00173139709362591

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

ISSN:0017-3134    

DOI:10.1080/00173139709362582

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor