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A modification of the Livingstone sampler, a thin—wall core sampler with stationary piston, will obtain long and undeformed cores of sediment from shallow lakes, with core diameters of 1 to 2 inches. Cores of 4—inch diameter up to 1½ m long can be taken with a piston sampler of slightly different design. The utility of both samplers is greatly extended by their use in combination with a drive frame and two lightweight chain hoists, which can provide up to 2 tons of force for driving and withdrawing the samplers.

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1992. A major floristic boundary in Minnesota: an analysis of 280 taxa occurring in the western and southern portions of the state. Can. J. Bot. 70: 319-333. A prominent floristic boundary is identified by combining distribution maps based on herbarium records of 280 taxa that occu; in western and southern Minnesota. A set of b o u n d a j dots was plotted for each taxon with the help of a grid overlay, and the coordinates of the dots in the set were tabulated and mapped by computer. The map shows a band of concentration of species limits that runs roughly north-south in the west and bends eastward in the central and eastern parts of the state. When subsets of the 280 taxa based on habitat preference are mapped independently, the band remains distinct. Single factors of climate and landscape alone are inadequate to explain the position and strength of the floristic boundary. The next most simple hypothesis proposes that the boundary results from an abrupt change in ecosystem type, from a woodland kept open by the interaction of fire with vegetation, topography, and soils to a closed forest where fire was less frequent. The concentration of limits implies that for many species migration had reached an equilibrium with ecosystem factors under the present climate. . 1992. A major floristic boundary in Minnesota: an analysis of 280 taxa occurring in the western and southern portions of the state. Can. J. Bot. 70 : 319-333. En combinant les cartes de distribution et les donnCe d'herbier de 280 taxa du sud et de l'ouest du Minnesota, les auteurs ont identifie une importante frontibre floristique. Une frontibre en pointillCs B CtC enregistree pour chaque taxon en superposant une grille, et les coordonnCes des points ainsi obtenues ont CtC tabulees et cartographiees par ordinateur. Les cartes montrent une bande de concentration de limites d'espbces qui coure gCnCralement du sud au nord dans la partie ouest et gagne vers l'est dans la partie centrale et vers l'est de 1'Ctat. Lorsque des sous-ensembles de ces 280 taxa sont cartographiks indkpendamment en se basant sur I'habitat, ces bandes demeurent distinctes. Les facteurs du climat pris un B un et le paysage seul ne peuvent expliquer la position et la force de cette frontibre floristique.L'hypothbse suivante, la plus simple, serait que la frontibre rCsulte d'un changement abrupte dans le type d'Ccosystbme, allant d'une forkt maintenue ouverte par les interactions du feu avec la vCgCtation, la topographie, et les sols, B une forkt oh l'incendie est moins frCquent. La concentration des limites implique que pour plusieurs espbces la migration a atteint un tquilibre avec les facteurs CcosystCmique, sous le climat actuel.