The effect of density on individual and population fertility, and selected morphometric characters (height, number of: ramifications, generative branches, inflorescences and leaves) of Echinochloa o-us-gaili plants was studied in a glasshouse. A decrease in individual fertility was observed in all density variants examined, but it did not result in a decrease in population fertility per unit of area. In response to worse developmental conditions there appeared plants characterized by reduced height and simplified external conformation.

Content of total phenols in not treated plants of Chenopodium album biotype susceptible to atrazine was 40% higher compared to resistant one. Atrazine applied at 1 kg per hectare increased the amount of these compounds in both biotypes, especially as regards on the level of monophenols in susceptible biotype, which was 3 times higher than in untreated plants. Amount of monophenols in atrazine-resistant biotype increased slightly due to atrazine application. After application of atrazine the polyphenols/monophenols ratio decreased from 4.2 to 1.1 in susceptible biotype, while it was not much changed in resistant biotype. Atrazine increased the content of flavanols in S biotype eight-times compared with untreated plants, while in resistant one this phenomenon was not observed. IAA-oxidase activity measured in vitro was modified by leaf extracts from C. album and Echinochloa crus-galli. Than the extracts from triazine-treated resistant biotype were more capable of protecting the indoloacetic acid (IAA) against enzyme activity. It may suggest that the mechanism susceptibility or resistance to herbicide is not only involved with PS II complex, but consists also in formation in plant the systems which favour or protect the auxin degradation, respectively.

The aim of the study was to investigate the effect of some different environmental conditions prevailing during the development and ripening of Echinochloa crus-galli diaspores on their germination. Some seeds were tested in the autumn the same year, whereas others were divided into two groups: dispersed seedsand seeds within the inflorescence. Then the seeds of both groups were buried. After eight-month stratification in the soil, the diaspores were tested under the same conditions as the samples examined in the autumn. The seeds tested in the spring germinated faster than those tested in the autumn. Also the germination capacity of barnyard grass caryopses examined in the summer was almost twofold higher than the germination capacity of those examined in the autumn. Both autumn and spring tests revealed that the harvest time affected germination. The seeds obtained in the second half of August and at the beginning of September (in the middle of the growing season) were characterized by a higher germination capacity than the caryopses collected at the beginning and the end of the reproduction period. The results show that the germination capacity and rate were not influenced by the place of origin, habitat conditions and accompanying plants. It was found in spring tests that germination depended on the kind of dissemination unit stored in the soil. After eight-month soil stratification, dispersed caryopses germinated by approx. 20% better than those stored with a part of the inflorescence.