OF SOUTH AUSTRALIA. 
13 
Cymodocea (also belonging to the family Potamogetonaceae) has a 
creeping rootstock, which sends up erect leafy stems at intervals. The 
stems are hard, almost ligneous, branched, 15-30 cm. high, the stem and 
branches naked below, marked with the scars of fallen leaves, and 
terminating in leafy pinnate bunches. The leaves are alternate, stiff, 
linear, 2. 5-7.5 cm. long, truncate at the end and sheathing at the base, the 
junction of the lamina with the sheath being marked with a transverse 
line, along which the lamina falls off. The flowers are solitary, the male 
and the female separate, hidden in the leaf-axils without a proper perianth. 
Male flowers of 2 sessile, two-celled, anthers. Female flowers of 2 distinct 
carpels, each capering into a slender bilobed style, each bearing one ovule. 
Fructification various and in some species unknown. 
C. antarctica Bndlicher (G. zosterifolia F.v.M.) is the species found on 
the South coast of Australia. It grows gregariously in deeper rock pools 
and in shallow waters. Its stems and branches are often beset with many 
varieties of seaweeds, especially the Corallines, Corallina, Jania, and 
Metagoniolithon. Its fructification is almost viviparous, the embryo ger- 
minating within the carpel and producing a young plant which finally 
breaks away and anchors itself by its ‘ 1 comb ’ ’ to the bottom of the sea. 
THE TRUE SEAWEEDS OR ALGAE. 
Seaweeds play a part of the utmost importance in the scheme of Nature, 
and incidentally may be of great direct service to Man. 
THE WORK OF SEAWEEDS IN NATURE. 
The larger seaweeds abound in the debatable ground of the foreshores 
of the whole world; microscopic forms exist in untold myriads on the 
surface layers of the oceans. All form and contain chlorophyll, that 
wonderful substance, the only substance known which, under the action 
of light, can manufacture food out of inorganic material. Seaweeds draw 
all their supplies from the seawater which surrounds them — water, 
oxygen, carbon dioxide, and mineral salts. In the light, the chlorophyll 
decomposes the carbon dioxide, setting free a large part of the oxygen 
and retaining the carbon for the uses of the plant. The exhalation of 
this oxygen into the surrounding water keeps the balance of the dissolved 
gases, so that the sea animals can obtain plenty of oxygen for respiration. 
Further, Galaxaura, Halimeda, and the Corallines absorb the carbonic 
acid, and form carbonate of lime which they incorporate in their tissues, 
thus removing it permanently from the sea water. Thus the seaweeds 
keep our harbour waters pure, and available for the life of fish and 
invertebrates; they absorb the excess of the detrimental carbon dioxide 
which is always being given off in the respiration and decay of animals, 
