Auxin is believed to be a critical determinant of the differentiation and connectivity of vascular tissue. The auxin canalization hypothesis states that auxin flow through provascular tissue promotes its differentiation into vascular tissue, which increases auxin flow through these cells. The positive feedback between auxin flow and vascular development results in channeling of auxin flow to a small set of connected cells, ensuring the continuity necessary for proper function of the vascular system. This hypothesis is supported by the effects of experimental perturbation of auxin flow by wounding or auxin transport inhibitors. Further support comes from defects in vascular tissue formation and alignment seen in various auxin-related mutants of Arabidopsis. A direct correlation between vascular development and IAA concentration has been observed in the trunks of Scots pine and hybrid aspen, where IAA concentration is highest in the vascular cambium.