(a) Branching from almost every hollow segment.∗∗ “Hollow segment” is the term used by Fritsch (1945) in contrast with “solid tissue.” As pointed out by Mollet (1880) node and internode are not very appropriate names for the parts. The swollen portion has been referred to as the receptacle (Osborn. 1948). But this term is hardly suitable where no functional conceptaeles are present. (b) Multiple branching much more common than dichotomous; a dozen buds may arise from one segment. (c) Branching from solid stalks as well as from hollow segments. (d) Incomplete division of hollow segments giving odd shapes and some flattening. (e) Renewed branching from mature parts, both solid and hollow. (f) No equivalent of the spirality seen in salt marsh fucoids (Baker, 1912). 3. Vegetative multiplication. With such close polychotomous branching, the decay of a hollow segment as when embedded in mud, or the breaking of any one of the solid nodes owing to the great weight of the proliferating thallus, leads to division into at least two parts, often more. Detached pieces continue to grow, at times showing some tendency to bipolarity, as when young segments develop from the broken end of a solid node (Pl. 9. Fig. 3). 4. Floats. The cavities in the thallus contain watery mucilage, but in normal plants a number of them contain also some gas, and float easily. No part of the loose-lying plants shows any tendency to float up in sea water and only a few of the cavities contain any gas. This lack of buoyancy combined with prolific budding and crowded branching results in the formation of plate-like clumps thicker at the edges and with the majority of the young buds round the periphery, facing upwards. Outwards and downwards (Pl. 9, Fig. 2). 5. Size. Hollow segments of 7 × 6 mm. to 13 × 12 mm. fall well within the ranger of size usual in Hormosira banksii; occasionally an old flattened central segment is as much as 25 mm. across. Plants, however, reach a much greater bulk than is usual. A portion of one clump, probably less than half of it, weighed more than 6000 grams when drained; its single branch systems measured up to 25 cm. or 22 segments long. The number of segments increases of course in geometrical progression from within outwards. And this portion alone had several thousand budding tips. 6. Sterility. Hair-pits are visible in some, but not all hollow segments. They are few in number, small, with narrow cavity, small ostiole, and few hairs arising in part at least from the bottom of the cavity (Pl. 9. Fig. 2B). They probably represent the “cryptostoma” stage in the development of the conceptacle described by Osborn (1948), No well-developed conceptacles were seen, and the plants appear to be sterile.