114 
THE SEAWEEDS 
a type of Red is Batrachospermwm , a mass of branching gelatinous filaments 
bearing verticils of brownish to greenish branchlets. In salt-water, how- 
ever, this state of affairs is reversed, and whilst in a cursory examination 
of a marine flora the coarser Browns are the most strikingly obvious, yet 
as far as the number of different species is concerned, the Reds pre- 
dominate. Lucas estimates that the percentage proportions of the various 
classes in Australian waters are approximately: Greens 11 per cent, Browns 
19 per cent, Reds 70 per cent ; so that it may be seen that the Reds contain 
more than twice as many species as the Greens and Browns together. 
Among the Reds there is great range and diversity of the form of the 
thallus, and whilst some adult thalli hardly cover a sixpence, some, e.g., 
Cathy menia, have a spread of up to 4-5 square feet, but none reaches the 
immense proportions of some of the coarser brown kelps, e.g., Sarcophycus 
(bull kelp of Tasmania). In structure the thallus is multicellular, dendroid 
or forming flat leaf-like expansions, the filaments of cells being united in 
a gelatinous matrix or closely compacted with an inter-cellular cementing 
substance so that in section the frond assumes a pseudo-parenchymatous 
appearance. Unfortunately there are so many variations in the organiza- 
tion of the thallus that a superficial examination of the form and 
appearance of the plant may give no clue whatsoever to its true taxonomic 
position; hence to establish a complete specific identification, in addition 
to its morphological features some embryological data are also required. 
The group suffers, too, from the fact that a large number of species are 
very ill-defined, and seem to merge into one another in a series of gradations, 
and also that a large number of the species enumerated by early workers 
in this field are very incomplete or leave much to be desired in their species 
description, so that positive identification of these plants is often well-nigh 
impossible. 
Although the Algae are generally regarded as a primitive and fairly 
simple group, the cytology of the Reds is by no means simple, and many 
of the metabolic and respiratory processes of the cell are still practically 
unknown, but this is principally due to the fact that so little exact work has 
been done on them. The innermost cells of the thallus are nucleate, clear 
and colourless, sometimes apparently empty and sometimes containing 
storage products, e.g., Floridean starch, while the outermost cells contain 
the pink chromatophores, and are the assimilators, deriving their food 
supplies directly from the surrounding water, and these apparently are 
the seat of synthesis of metabolic products required by the plant. In the 
chromatophores, in addition to phycoerythrin, the chlorophylls a and /3, 
xanthophyll and carotene are present while in addition, in some species, 
there are small amounts of phycocyanin which chemically is closely related 
to phycoerythrin. As yet there is conflicting evidence regarding the precise 
role of phycoerythrin in the algae, and although it is possible that it plays 
some vital role in the life of the plant, just what this is exactly is not 
known. It has been suggested that it is the determining factor enabling 
the red alga to carry on its processes of photosynthesis under conditions 
