THE REPRODUCTIVE-BIOLOGY OF KAURI (AGATHIS-AUSTRALIS) .1. POLLINATION AND PREFERTILIZATION DEVELOPMENT

The stages of pollination, ovule and megagametophyte development, and pollen tube penetration of the nucellus are described for Kauri (Agathis australia [Lambert] Steud.) growing in New Zealand. Kauri has a 2-yr reproductive cycle with pollination and ovule initiation occurring in October and fertilization about 1 yr later, and seeds mature about March of the second year. Pollen germinates on the bract in December or January and forms a 5-6-mm pollen tube that grows to the micropyle. During ovule development the nucellus grows out of the micropyle. Pollen tubes grow over the exposed nucellar surface, then in March penetrate the nucellus and grow around the megagametophyte. Megaspore meiosis occurs in December, and a free nuclear megagametophyte develops by March. This is followed by a 4-5-mo period when little development occurs. The megagametophyte develops rapidly in September and is mature in October when fertilization occurs. Archegonial development and ultrastructure are described and discussed in relation to other conifer families.