The master's thesis comprises of a detailed study on the development of geranium adventitious root system of different hybrids (upright and hanging). An observation of the key auxins formation dynamics during the development of adventitious root system, indole-3-acetic acid (IAA) and its metabolite indole acetyl aspartate (IAA-Asp) was made. The development of callus and the quality, as well as the architecture of the adventitious root system, was studied with regard to the exogenous application of cuttings before inserting in substrate with several auxin substances usually used in practice. When producing seasonal plants, 'Ready-rooter' cuttings which have a callus already developed at the base of the cutting are considered as a high-quality planting material. Subsequent rooting in these cuttings is faster and more successful and, as a result, the growing period is shorter than for non-callusing cuttings. Based on auxin analyses, the average auxin contents in different time periods after severance was obtained. The study has shown that the average IAA content increased during the insertion of cuttings in substrate and remained high for up to 4 hours after the insertion. After 4 hours, the content was considerably reduced. The increase of IAA should be moderate, considering that too high contents can lead to the underdeveloped adventitious root system. A decrease in IAA content in later stages of development is necessary, due the high IAA levels can slow the root development. Morphological observations have confirmed that the cultivar has a significant influence on the development of adventitious root system and on the IAA level course. The development of callus and adventitious root system was faster in 'Tango Dark Red' and 'Caliope Dark Red' cultivars than in 'Feuer Cascade' cultivar. The statistical analysis of the results showed that the 'Feuer Cascade' variety had a much higher average endogenous auxin content in the cuttings in comparison to the average auxin content of the 'Tango Dark Red' cultivar. This can probably explain the more difficult rooting capacity of the 'Feuer Cascade' cultivar.