SEM observations of 12 species of the genera Triticum, Hordeum, A\•ena, Secale, Panicum, Setaria, Bromus and Glyceria contribute to a better understanding of the exine sculpture and lead to the description of 4 types. No fundamentally new features were revealed and the scope of SEM may be limited to that context. A higher degree of reliability in the identification of the pollen types may be achieved if all available Ll\1 and SEM characters are combined and if the ecological differences of those wild grass species ranging within the pollen size of cereals are taken into consideration as an exclusive factor. Finally the existence of a taxonomic patterning of the exine sculpture is confirmed.

No abstract

, 1969;Weiss & Lagaly, 1967) have shown that their method of determining the layer charge of layer-silicates by measuring the basal spacings after intercalation with n-alkylammonium salts is superior to classical methods based on chemical analysis and CEC. However, in the past 10 years only a few clay mineralogists have used the n-alkylammonium method. One reason may be the very time consuming procedure. The purpose of this note is to describe improved methods of preparing the n-alkylammonium chlorides and of intercalating the clay minerals. Preparation of the n-alkylammonium chloridesWe have found the following procedure for preparing the n-alkylammonium chlorides to be better than that of Weiss et al. (1971) because it yields pure, crystalline powders which can be stored indefinitely.Place a mixture of equal volumes of the appropriate n-alkylammonium salt and ethanol (95~) into a round-bottom flask. Place the flask in a circulating water bath and insert a thermometer. Slowly bubble gaseous HC1 through the mixture. The temperature must not exceed 65~ this can be regulated by adjusting the flow of gas (bubbling the gas through conc. H2804 makes adjustment of the flow rate easier). The temperature will generally stabilize during the reaction but as the equivalence point is approached, it will begin to drop. At this stage begin testing for the end-point (pH ~< 7) by placing a drop of the solution on a piece of litmus paper. When a pH of 7 or less is obtained, remove the thermometer and bubbling tube and connect the flask to a rotating vacuum evaporator.With the rotating flask in a 60~ water bath, evacuate the system with an aspirator. The excess of HC1 and ethanol will evaporate and the n-alkylammonium chloride will crystallize. Do not evaporate to dryness because hard clumps will form which are difficult to break down. Instead, disconnect the flask from the vacuum when the slurry begins to stop flowing.Transfer the slurry to a vacuum filter apparatus using cold acetone ( -20~ Wash the crystalline powder with the cold acetone until the leachate becomes clear. The powder will dry completely in 4--8 h at 60~ The dry powder can be stored indefinitely in stoppered glass bottles.Fresh aqueous solutions of the n-alkylammonium chlorides can be prepared as needed. The solution concentration suitable for the exchange reaction depends on the chain length. Optimum concentrations are given in Table 1. The solutions should be stored at 65~ so that they remain fluid and ready for use. The solutions will keep for 3-4 months at this temperature.

Untersuchungen des Pollens von 69 Belegen aus 44 Arten oder vermeintlichen Arten der Gattung Waltheria führten auf Grund von Unterschieden im Exinebau zum Nachweis eines spinulosen und eines suprareticulaten Pollentyps. In beiden Typen zeichnen sich ± parallele Tendenzen in der Evolution des Apertursystéms ab, die auf eine Vermehrung der Aperturen, auf eine Verkürzung der Colpi und auf eine deutlichere Begrenzung und nexinöse Verdickung der Ora gerichtet sind. Sie belegen damit wesentliche Schritte der Aperturevolution, die beim spinulosen Typ vom zonocolporaten über den zonopororaten zum pantopororaten, beim suprareticulaten Typ vom zonocolporaten zum pantocolporaten Status verlaufen sein dürfte. Die Tendenzen der Sporodermevolution laufen auf eine stärkere morphologische und teilweise auch regionale Differenzierung der Exineelemente (Bacula, Spinulae) hinaus, die eine bemerkenswerte Korrelation mit dem Evolutionsniveau der Aperturen erkennen läßt. Nach pollenmorphologischen Gesichtspunkten lassen sich die Arten der Gattung Waltheria in 2 Gruppen zusammenfassen, die als zwei verwandte, aber relativ selbständige Abstammungsgemeinschaften zu betrachten sind. Diese Befunde sprechen für eine taxonomische Untergliederung der Gattung. Die Pollenmorphologie gibt weitere Hinweise für die Verwandtschaftsbeziehungen der Arten innerhalb dieser Gruppen und für die Abgrenzung und infraspezifische Differenzierung von W. indica.