494 AN INVESTIGATION OF THE LIFE CYCLE OF MACROZAMIA SPIRALIS MIQ. By P. Brough, M.A., D.Sc, F.R.S.E., and Maejoeie H. Taylor, B.Sc, Botany Department, University of Sydney. (Plates xiv-xvii; ninety-three Text-figures.) [Read 30th October, 1940.] An investigation of tlie life-history of Macrozamia spiralis was begun early in 1938. Two main reasons governed the decision to embark on the work, first, the fact that up to that time little had been published regarding this particular genus, and second, not-withstanding the voluminous literature on cycads in general, many important phases in their life histories remain to be described. In 1939 the authors presented a preliminary account of megasporogenesis in Macrozamia spiralis, and since then Baird, A. M. (1939), has published the results of her researches on Macrozamia Reidlei. Other investigators, namely. Chamberlain (1913) on Macrozamia Moorei and Light (1924) on Macrozamia Fraseri, have made contributions to our knowledge of the genus, but it is believed that the present comprehensive account embodies many facts of particular interest, relative not only to Macrozamia, but to cycads in general. Only those features which are new, or of special significance, are stressed, although other facts necessary to preserve continuity, and to make comparison with other genera are included. Distribution. The genus Macrozamia is confined to Australia and, in those districts in which it is most abundant, is the dominant plant over very considerable areas. It then forms a much more prominent feature of the flora than either of the other endemic genera, namely, Bowenia and Cycas. Macrozamia spiralis is widely distributed throughout the eastern coastal areas, extending from southern Queensland almost to the southern limit of New South Wales, a distance of approximately a thousand miles, and in number of individual plants probably exceeds that of any other cycadean species. Typically, it occurs in vast numbers in open eucalyptus forests from just above sea-level to a distance of several hundred yards inland. Occasionally, the species is encountered in isolated areas, each supporting some hundreds of plants, at a distance up to ten or fifteen miles from the coast, but, beyond that, this species is rare, although several small societies have been found as much as thirty miles inland. Habit and Habitat. Macrozamia spiralis finds its maximum expression on sand-dunes adjacent to the sea, or on ridges of light sandy soil formed by the disintegration of the underlying sand-stone, or by wind-borne shore sand. In such an environment only the major portions of the leaves and the cones appear above ground. The lower parts of the petioles, the younger leaves, and the organic apex are buried in the soil, as are, of course, the thick tuberous stem and deep root system (PI. xiv, figs. 2, 3). More rarely a society flourishes on hard quartzite or sandstone ridges, but then the resistant natui"e of the subsoil — chiefly rock fragments — retards penetration, and the stem, encased in an armour of leaf-bases, rises above the ground exposing a trunk up to four feet high (PI. xiv, fig. 4). Such plants are almost as massive and well-developed as those on softer soils. A comparative study of plants at various stages of development indicates that the continued burying of the apex in the softer soils is due to the action of contractile roots (Text-figs. 89-93). In hard stony situations this contractile force is evidently unable to overcome the resistance of the sub-soil, and so the stems protrude well above ground level (PI. xiv, figs. 4, 5).
BioStor
