Weed infestation was carried out in the vegetation of oilseed rape and winter wheat in the operating conditions. The aim was to observe a difference between between autumn and spring in the weed species composition in individual crops. Species Chenopodium strictum and Thlaspi arvense were identified in the vegetation of oilseed rape in autumn and species Capsella bursa-pastoris and Tripleurospermum inodorum during spring. Species Euphorbia cyparissias, Stelaria media and Rumex crispus were found in winter wheat during autumn. Results, which are not statistically significant, show that there is a relation between the density of winter crop vegetation and the weed species composition. Species Chenopodium strictum, Thlaspi arvense, Triticum aestivum and Tripleurospermum inodorum occurred in sparse population of oilseed rape. Species Lycopsis arvensis and Polygonum arenastrum were found in denser vegetation of oilseed rape. Species Avena fatua, Stelaria media and Thlaspi arvense were observed in sparse population of winter wheat and in denser species Geranium dissectum and Erodium cicutarium.

The presence of triploid individuals, whether hybrids arising from crosses of diploid and tetraploid plants, or spontaneously generated triploid hybrids diploid populations, is increasingly important in plant populations. However, the possible evolutionary role of the triploid hybrids is closely connected to the frequency of their occurrence, to their relative fitness (compared to parental cytotype) and fertility. As a model plant I choosed Tripleurospermum inodorum, in which a relatively frequent occurrence of triploid hybrids was documented in mixed populations of tetraploids and diploids. This annual plant achieves realy quick its reproductive maturity and is easily cultivated, making it an ideal model for cultivation and pollinating experiments. Compared to parental cytotypes, the triploid hybrids of T. inodorum take approximately the same (mostly mediated) fitness values. In vitro conditions were cultivated to measure of germination rates. Germination rate of triploid seeds was comparable to diploid parental cytotype. In the subsequent comparative cultivation, nearly 150 plant individuals (2x, 3x, 4x, and aneuploid cytotype) in the greenhouse showed that the triploids had intermedial values of their parental cytotypes or close to one of the parents. Thus, the vitality of the triploid plants is...