OF SOUTH AUSTRALIA. 
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of poor light, but the evidence is by no means clear cut. Due to the presence 
of phvcocyanin in some of the Reds, and of phycoerythrin in some of the 
Blue-greens, it has been suggested that the two groups arose side by side, 
possibly even from some common stock, but while the close relationships 
of the two groups are stoutly affirmed by some pliycologists, others are 
equally dogmatic in denying them upon grounds of lack of other con- 
firmatory evidence. 
Among the higher Reds (Euflorideae) there is also a complicated system 
of protoplasmic connections between adjacent cells. This generally takes 
the form of a central pit on the transverse walls closed over by a thin 
membrane, on either side of which the protoplasm forms denser, gel-like 
plates with strands passing directly through minute perforations. In this 
way the protoplasm of the filament is really continuous rather than the 
individual cells forming separate identities, resulting in the formation of 
a symplast in which there is a direct interchange of dissolved solutes, 
although cell inclusions, nucleus, chromatopliores, etc., are unable to pass the 
barrier. This state of affairs is reminiscent of the connections of the sieve 
tube elements of the phloem (bast) of higher plants. Growth of the thallus 
occurs as an increase in length of the individual filaments from apical 
growing points. 
Marine algae are subject to more even environmental conditions than 
many groups of higher plants. The open ocean provides a remarkably 
constant set of physical conditions over the whole globe. The surface 
temperature is never lower than 1° C. nor higher than 28° C., while at 
greater depths the temperature shows even less variation. The alkalinity 
(pH) of sea-water is remarkably constant as is the salinity which in turn 
determines its osmotic pressure. Along the coast where rivers flow into the 
sea there is a constant dilution of the sea-water, and the salinity is not quite 
as high. Here also the heating and cooling of the land masses will give rise 
to slightly greater fluctuations in temperature, but even so the sea provides 
a remarkably constant environment for life. The Rhodophyeeae are com- 
paratively insensitive to temperature variations, being world wide in 
distribution and occurring in abundance in both tropical and polar seas, 
although it is in the latter that they reach their maximum development . On 
the other hand, the Chlorophyceae are more sensitive to temperature and 
predominate in tropical oceans, while they are conspicuous by their absence 
in the polar seas which are essentially Rhoclophycean. The Rhodophyeeae 
are essentially plants inhabiting gloomy regions where little light penetrates, 
and so predominate in the depths of the ocean or in marine caverns and 
rock holes, and do not form as a rule any marked littoral zone which 
is such a prominent feature of the Browns. Some Reds do, however, 
flourish even above the high-tide limit, e.g Catcmella, Caloglossa and 
Bosirychia, where they are only occasionally wetted by ocean spray. As 
yet little work has been done upon the marine ecology of the algae, but 
in a shaded rock pool or marine cavern there is quite a marked change from 
the common littoral flora to one predominantly of Reds more usually 
