CASUARINA  , a genus of trees containing about 30

species, chiefly Australian, but a few Indo-Malayan . The long whip-like green branches are longitudinally grooved, and bear at the nodes whorls of small scale-leaves, the shoots resembling those of Equisetum (horse-tail) . The flowers are unisexual; the staminate are borne in spikes, each flower consisting of a central stamen which is surrounded by two scale-like perianth-leaves . The pistillate are borne in dense spherical heads; each flower stands in the axil of a bract and consists of two united carpels flanked by a pair of bracteoles; the long styles hang out beyond the bracts, and the one-chambered ovary contains two ovules . In the fruit the bracteoles form two woody valves between which is a nut; the aggregate of fruits resemble small cones . Pollen is transferred by the wind to the long styles . The pollen-tube does not penetrate the ovule through the micropyle but enters at the opposite end—the chalaza . This anomaly was 1 Dicotyledons . Angiospermae- Porogamae(Monocotyledons . Chalazogamae (Casuarina) . The names of the two subdivisions recall the manner of entrance of the pollen-tube . More recent investigations, chiefly by Nawaschin and Miss Benson, on members of the orders Betulaceae, Fagaceae, Juglans and Ulmus, showed a recurrence in a greater or less degree of the various anomalies previously observed in Casuarina, and suggest that the affinity of Casuarina is with these orders of Dicotyledons .

The

wood is very hard, and several species are valuable timber trees . From a fancied resemblance of the wood to that of the oak these trees are known as " oaks," and the same species has different names in different parts such as " she-oak," " swamp-oak," "shingle-oak," "river-oak," "iron-wood," " beef-wood," &c . See J . H . Maiden, Useful Native Plants of Australia (London and Sydney, 1889) .