In shoots with spiral phyllotaxy axial homodromy occurs when ontogenetic helix continues its course in successive flushes of the axis. The opposite case is axial antidromy when the helix course alters every year. Initially, we thought that in conifers axial homodromy occurs without exception, suggesting that the apical meristem is not autonomous in a process of primordia formation but is influenced by the older, well-developed parts of the shoot. Recently, however, we have discovered that in Torreya nucifera characterized by bijugate phyllotaxis the direction of ontogenetic helix is every year either the same or the opposite to that of the previous year. Discontinuity of organogenetic process in the region of bud scales, resulting perhaps from changing primordia identity, was considered to be one of the causes. The comparative studies showed that in genera with axial homodromy, such as Abies, Picea, Cephalotaxus and Taxus, phyllotaxy in a region of bud scales is as regular as in the area of normal leaves. In Torreya, however, the divergence angle between successive pairs of scales increases gradually leading to the decussate arrangement. Its symmetry guarantees the random selection of a new configuration of ontogenetic helix in a subsequent growing season. Another possible reason for the special behavior of Torreya is system of internal signaling. If the initiation of leaves is governed by the vascular system, then the axial homodromy should result from the system mature and close enough to this area where primordia are initiated. Torreya case might result from isolation of the meristem from the signals sent by vascular system. It appeared that indeed in Torreya, the topology of vascular strands and collenchymatous plate is such, that neither differentiated, nor the procambial, vascular strands penetrate the plate. In other conifers they clearly pass the plate reaching out for the level of lowest primordia.

Key words: chirality, morphogenesis, phyllotaxy, shoot apical meristem, Torreya, vascular system