ONTOGENY OF AXILLARY BUDS AND SHOOTS IN ROSES - LEAF INITIATION AND PITH DEVELOPMENT

The ontogeny of an axillary bud (in the middle region of a shoot) from initiation up to flowering of the subsequent shoot was studied. The f irst secondary buds appeared in the axillary bud (primary bud) when th e leaf subtending the primary bud unfolded. By that time, the primary bud contained seven leaves, including leaf primordia. During the devel opment of the parent shoot to the harvestable stage, the number of lea ves and secondary buds in the primary bud increased to 11 and four, re spectively. The primary bud appeared to contain the lower part of the future shoot. After release from correlative inhibition, all the leave s and a flower bud had been formed within 10 days. No internodal elong ation occurred between the scale-like leaves. Pith diameter was found to be correlated with the shoot diameter and was about 50% of the diam eter of harvestable shoots. In the primary bud the cells of the pith w ere isodiametric and equal in size; they were vital and contained star ch and sugars. Two weeks after release of the bud, the final pith diam eter was reached at the base of the shoot. Two types of cells had diff erentiated: small, vital cells and large, dead cells. The small cells, which appeared to form a network throughout the pith, could contain s tarch and sugars, the large cells were filled with air. The number of cells on a diameter line of the pith was constant after bud break and slightly decreased from the base towards the top of the shoot.