Detailed studies on the initiation and development of axillary buds inHeracleum andLeonurus have been reported in this paper.
Works so far done on this problem in Ferns, Monocotyledons and Dicotyledons have been briefly reviewed.
In Ferns an axillary bud is initiated in thedetached (apical)meristem on the free surface of the axis or “in proximity to meristele conjunctions“. In Monocotyledons initiation takes place in the surface layer of thecorpus, on the side opposite to the insertion of, and in association with, the leaf primordium just above the one in Whose axil the bud appears. Hence Hsü (1944) describes the origin as ‘endogenous’ in Monocotyledons. In Dicotyledons though Goebel reports origin from the embryonal meristem a little behind the apex, Koch, Majumdar and Datta report origin in the vacuolating cells of the adaxial epidermis of the subtending leaf opposite the median bundle inSyringa, Heracleum andLeonurus.
In the shoot apices of Ferns, Monocotyledons and Dicotyledons leaf primordia are laid down first and buds are initiated in their axils later. A year may elapse between the laying down of the axillant leaves and formation of buds in their axils as reported in the winter buds ofSyringa.
Bud trace originates in the bud primordium and then differentiates backwards into theleaf- cushion outside the axial ring of vascular bundles, finally it enters the ring to unite with one of its synthetic bundles.
As the buds normally originate in the axils of leaves which are removed some distance from the apex and which are growing vigorously or unfolding, it is suggested that their initiation is due to some physiological processes than to any specific qualities inherent in the apical meristem.