Related to phyllotaxis interlocked systems of vascular sympodia and cortical resin canals in Abies and Picea shoots

We report on some new aspects of the internal architecture of conifer shoot . proving that it is even more strongly related to phyllotaxis than was ini tially thought. The number of vascular sympodia in an open system of Abies and Picea shoots is correlated with the number of cortical resin canals. Bo th numbers are the consecutive members of the phyllotactic series. which de fines the phyllotactic pattern of the shoot. This means that the concentric systems of alternately oriented vascular sympodia and resin canals are int erlocked. following the course of superficial opposite parastichies. Such p attern of inner architecture most likely contributes to the mechanical stre ngthening of the shoot. It also provides a new example of heterogenetic ind uction in plant morphogenesis because the development of orderly spaced res in canals is dependent upon earlier differentiation of vascular system. A r apid method of assessing the number of vascular sympodia becomes available bq means of counting the number of discrete cortical resin canals visible o n the cut surface of the shoot sectioned transversely. Despite bring set up on the smaller radius. the number of sympodia is always one step higher in a phyllotactic series than the number of canals.