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F. E. Fritsch 
by the Phaeophyceae and Florideae. The same statements apply to 
the Cyanophyceae and, except as regards relative abundance, also 
to the Diatoms 1 . In short all those phyla which have been really 
successful in freshwater and terrestrial habitats exhibit no greater 
development in the sea than on land and are in fact, except in the 
case of Diatoms, relatively poorly represented in the former. Even 
the Siphonales, which exhibit a comparatively high vegetative 
development, are, in their reproductive features, on a lower plane 
of development than many Brown and all Red forms and in this 
respect are at a lower level than the freshwater representatives. 
These, Vaucheria and Dichotomosiphon , are the only oogamous 
members of the series 2 . Such forms as Trentepohlia, Draparnaldia, 
and Coleochaete, in one feature or another, show indications of higher 
equipment than is found in any marine Green Alga. 
In view of the dominance of Chlorophyceae and Cyanophyceae 
in freshwater and terrestrial habitats it appears warranted to 
conclude that for them conditions of life in such situations have been 
more favourable than in the sea, where perhaps they have been 
unable to hold their own against the more successful Brown and Red 
forms. These latter do not appear to take kindly to freshwater, and 
such few examples as are known ( Hildenbrandtia , Lemanea , Batra- 
chospermum , Lithoderma , etc.) are largely characteristic of rapid 
streams, many of the Red forms betraying their extreme light¬ 
sensitiveness by frequenting the underside of overhanging rocks and 
other shaded habitats. There is considerable probability in these 
cases of direct estuarine migration (Church, loc. cit. p. 8). 
Church holds the view that “the Green Algae surviving in 
freshwater are somatically the merest depauperated relics in the last 
phases of deterioration, as reduced filamentous and disc-types” 
(p. 8). Presumably he would apply the same explanation to the 
Blue-green Algae, for on p. 32 he speaks of “the flora of freshwater 
ponds and freshwater Algae, presenting types of organism so far 
removed from their original condition.” That series of reduction of 
filamentous forms can be recognised in some of the lines of Chloro¬ 
phyceae is unquestionable, but there is no evidence of reduction in 
the group as a whole, that is to say there is nothing to show reduction 
from forms organised on a higher somatic basis. The groups Chloro- 
1 Church (loc. cit. p. 47) cites the marine Schizonemas and Licmophova as 
instances of higher organisation amongst marine Diatoms, but the difference 
as compared with some of the freshwater colonial forms is not very great. 
2 Sphaeroplea might be added, but it is doubtful whether it belongs to 
this series. 
