A Morphological Investigation of the Unusual Cryptogeal Germination Strategy of Bunya Pine (Araucaria bidwillii)-An Australian Rain Forest Conifer

Abstract

The morphology of the cryptogeal germination sequence of Araucaria bidwillii (bunya pine) was studied. Individual seeds were 5-6 cm in length and 2.5-3.5 cm in diameter and had an average fresh weight of ca. 16 g. In mature seeds the embryo consisted of a cotyledon tube, hypocotyl, and root cap that were 3-5 mm in diameter and 25-30, 3-4, and 5-7 mm in length, respectively. The embryo was surrounded by, but not fused into, a massive megagametophyte. Germination was rapid as a large diameter pseudoradicle emerged from the seed 48 h after the start of imbibition. At 1 wk the cotyledon tube had elongated to 3.5 times its original length. As cotyledon growth was positively geotropic the root and shoot meristems were forced out of the seed and buffed in the soil below the initial position of the seed. At week 3 the hypocotyl was 12-15 and 3-4 times its original diameter and length, respectively, and had developed into a parenchymatous tuber. It appeared that starch stored in the megagametophyte was being mobil...