Modes of shoot extension and morphology of annual shoots in the persian walnut, Juglans regia L. 'Lara' (Juglandaceae)

Shoot extension during a growth season has been investigated in three morph ological types of floriferous annual shoots (monocyclic with or without a s mall axis with immediate development and bicyclic) on four types of parenta l branches within 4-year-old Juglans regia L. 'Lara' growing in the south-w est of France. The morphological type of parental branches has an influence on the time of inception of monocyclic shoot extension. No correlation has been found between the parental shoot length and monocyclic shoot length, while a positive correlation has been found between parental shoot length a nd bicyclic shoot length. Bicyclic annual shoots expand during two successi ve flushes : in spring and summer, respectively. The intra-annual resting p hase results in the presence of a series of cataphylls in the median part o f the shoots. Spring shoots and summer shoots may be distinguished by varia tions in form and in number of foliar organs. Annual shoots exhibiting an a crotonic axis with immediate development or a summer shoot generally posses s greater extension periods and lengths of spring shoots than the unbranche d ones.