Proportion Of Pollen Grains Research Articles

Role of the Generative Cell in Androgenesis in Henbane

When anthers of henbane containing uninucleate pollen grains were cultured, a large number of embryoids originated exclusively from the division of the generative cell. In a small proportion of pollen grains, both generative and vegetative cells contributed to embryoid formation. Embryogenesis by segmentation of the vegetative cell alone was rarely observed.

Recent pollen assemblages from the Western Interior of Canada

Pollen spectra have been compiled for samples of surficial mud from over one hundred lakes in the Western Interior of Canada. The area of the survey extends from the low-arctic tundras of Keewatin to the grasslands of southern Manitoba and Saskatchewan, including all the major landform-vegetation types. The purpose of the investigation is to provide a basis for the method of direct comparison in the interpretation of Holocene pollen spectra recovered from sites in mid-western North America. The pollen data are accompanied by qualitative and quantitative accounts of the vegetation of the several zones in the region. Spectra from arctic and subarctic zones include substantial fractions of arboreal pollen of southern origin. Tundra spectra are distinctive, showing high relative amounts of pollen of dwarf birch and sedges, as well as consistent but low frequencies of ericoid and graminoid pollen. Forest-tundra assemblages are not always clearly distinguishable from those of adjacent zones, but they show substantial proportions of pollen grains of alder, dwarf and arboreal birch, spruce and sedges. The continuous boreal forest region shows in general a predominance of conifer pollen in the spectra. Broad-leaved deciduous forests, represented very poorly in this region, are distinguished by the high values of pollen grains of oak, birch, elm and ash. The pollen of poplar, which is the dominant tree of the park-land of the nemoral zone, is absent or very poorly represented in lake mud samples. Grasslands show spectra dominated by pollen of grasses and herbs.