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In the paper the author attempts to carry out a comparison between the floristic composition and structure of plant communities present in cereal crops of the rural areas of the Siedlce Upland and the floristic composition and structure of the analogue plant communities found in the area of Siedlce, which is the biggest town of this geographic mesoregion. Tables of the following syntaxons were analysed in the comparative analysis: Papaveretum argemones, Papaver argemones-Vicia tetrasperma, Vicietum tetraspermae scleranthetosum and Vicietum teraspermae typicum. It was observed that the urban plant communities had a greater floristic variety, a greater participation of perennial and ruderal species, as well as, a more complex phytosociological structure, with the exception of few typical patches, comprising diagnostic species of various syntaxons.
Attempt of comparative analysis of the segetal flora of Siedlce City with similar flora of areas of arable lands of the Siedlce Upland is presented in the paper. Received results show the larger value for urban flora of apophitysm coefficient - 63,3% (61 % for Upland), flora modernization - 0,52 (0,42 for Upland) and flora labii1ity - 19 (15 for Upland). On the other hand segetal flora of the Siedlce Upland is characterized by largersynanthropization coefficient - 104 (93 for the city). As to other differences, considerable larger participation of perennial species in the flora of the city (45,5% Siedlce; 37,1 % Upland) is noteworthy. Moreover the occurrence of juvenile forms of arborescent species and plants running wild from dens and parks, e.g.: Mathiola incana, Aesculus hippocastanus, Sedum reflexum, Nigella damascena, Helianthus tuberosus among species weeding urban cultivation clearly noticeable.
The study of the morphology of pollen concerned eight species of the genus Taraxacum. Seven types were chosen with a different number of chromosomes belonging to the section Palustria: Taraxacum paucilobum 2n = 3x = 24, T. subdolum 2n = 3x =24, T. subpolonicum 2n =3x = 24, T. vindobonense 2n = 4x = 32, T. trilobifolium 2n = 4x = 32, T. mendax 2n = 5x = 40, T. portentosum 2n =? and one type from the section Obliqua – T. platyglossum 2n =?. Pollen from all the examined species was observed by SEM microscopy. A distinct relation exists between the morphology of pollen and the way of reproduction. Pollen of triploidal species, being compulsory apomicts, is characterized by a great variability of the size and a high percentage of deformed pollen grains. Tetraploids, being optional apomicts, produce regular pollen with a relatively even size. The regular type of pollen in pentaploidal Taraxacum mendax and in species with an unknown number of chromosomes (Taraxacum portentosum and T. platyglossum) suggests that these taxa are optional apomicts.
Studies on sexual dimorphism in reference to vegetative features and on the sex ratio in different environmental conditions were carried out in lowland populations of dioecious species Aruncus sylvestris. It was shown that female individuals of Aruncus sylvestris produced higher flowering shoots, longer inflorescences, more leaves and longer and broader leaves than the male ones. All listed differences were statistically significant. In populations of Aruncus sylvestris growing in optimum ecological conditions (fertile and wet soil, half-light) the sex ratio M/F is close to 1:1. Changes of ecological conditions along the gradient of fertility, habitat moisture (estimated by the types of phytocoenoses) and intensity of solar radiation caused marked drift of sex structure towards the male domination. Light intensity was the crucial factor for the sex ratio in studied populations. Populations growing in half-light showed sex ratio M/F ≈ 1:1 irrespective of habitat. Those growing in shade and in full light showed significant shift to male dominance. The largest deviation from 1:1 sex ratio (M/F ≈ 1.0:0.2) was observed in extremely unfavorable habitat conditions (full sun irradiance, dry soil, strong competition from Elymus repens (L.) Gould). Obtained results demonstrated that female individuals of Aruncus sylvestris had markedly higher habitat requirements compared with the male ones.
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