In monopodial, regularly branching system of coniferous shoot, exemplified in our studies by Picea and Abies, the chirality of spiral phyllotaxis in the supporting axis is correlated either positively (homodromy) or negatively (antidromy) with that of the laterals. As neither of these two tendencies prevailed in the investigated material, it seemed that the supporting axis has no effect upon the phyllotaxis of laterals. This conclusion appeared justified especially in light of the fact that phyllotactic system of each lateral branch is generated from the initial opposite arrangement of prophylls. Thorough anatomical analysis of primary vascular system structure in branching shoots of Picea and Abies unexpectedly showed that the above conclusion should be falsified. In vascular pattern where inclination of vascular sympodia is dependent upon phyllotaxis and anatomic diameter of the shoot we found 100% vascular homodromous correlation between the inclinations of vascular sympodia in axes of all orders. This homodromy was particularly spectacular in the cases when, in the main axis, the orientation of sympodia was changing ontogenetically bringing up immediately the new orientation of vascular sympodia in laterals. In the unknown way the vascular system of the supporting axis signals the axillary meristem, recognizing its size, what the chirality of its phyllotaxis should be, to accommodate the same inclination of its future vascular sympodia. These findings point out to the leading role of the vascular system in establishing phyllotactic pattern of the shoot.

Key words: chirality, conifers, ontogeny, phyllotaxy, primary vascular system, shoot