CONE DEVELOPMENT IN LIBOCEDRUS (CUPRESSACEAE) - PHENOLOGICAL AND MORPHOLOGICAL ASPECTS

Cones in Libocedrus plumosa are initiated in New Zealand in February ( late summer) and continue to develop through winter. The ultimate pair of bracts protrude and continue extension growth while the apex remai ns flat. Ovules are initiated in two pairs in July on the cone apex (i .e., are axial in origin), alternate with the upper two pairs of bract s. Ovule differentiation proceeds rapidly to the stage of pollination; the cone apex may develop further as a short columella. Soon after ov ule initiation an adaxial ligulelike outgrowth of each member of the u pper two pairs of bracts is initiated, that of the ultimate pair being broader than that of the lower pair. By intercalary growth of each li gule base an enlarged structure is developed, displacing the bract int o a lateral position and forming the four scales that enclose the deve loping seeds in a valvate manner. Cone and seed maturation follows wit h seed dispersal in March, approximately 1 year after cone initiation. The results show that there is no morphologically discrete ovuliferou s scale, and there is no ontogenetic fusion of discrete separate struc tures. The vascular system of the scale complex develops after the ovu les are initiated and forms a single series of vascular bundles with i nversely oriented xylem and phloem; this and other histological change s are the result of the activity of the intercalary growth process and do not relate to primary structures. The results are discussed in rel ation to existing knowledge of cone development in Cupressaceae, in wh ich axially borne ovules are common.