Phyllotactic patterns and transitions in Abies balsamea

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Abstract
Pgtllotactic patterns, as indicated by the number of helices in opposed parastichy pairs, were determined in elongated shoots. Twelve patterns were found, including very rare patterns such as tetrajugy and secondary bijugy. Typically, the same pattern was repeated each year along a particular axis. Changes in pattern occurred between annual growth increments, more rarely within one increment. Pattern changes were not radom, rather they occurred in a manner that minimized the change in the number of helices in the opposed parastichy pairs. A reversal in the direction of the ontogenetic helix often accompanied a pattern change.