190 
Simmons, Remarks about the Relations of the Floras etc. 
and the otlier genera must rest a matter of speculation, at all 
events Laminaria must be regarded as a young genus, where 
the differentiation of species lias not yet reaclied its end. % That 
L. solidungula really is the first Laminaria may be possible, 
even if there are other species that can be regarded as equally 
primitive, but the ancestor of the wliole family it can hardly 
be. It must be assumed that the origin of the Laminariaceae 
is polypliyletic as far back as \ve have any possibility to follow 
their phylembryons — of course their lineage will converge 
somewliere down against the base of organic life, perhaps among 
the Flagellatae. 
Having now tried to show how the two families, which are 
especially characteristic for the northern waters contribute with 
regard to their distribution in an unmistakeable manner to con- 
firm the opinion previously arrived to by examination of greater 
parts of the fioras, I will summarize the results as follows. 
The now existing joint appearance of species in the North 
Atlantic and the North Pacific must be due to the emigration 
to botli sides from the tertiary Polar Sea. Only in very few 
cases this Community of species allows another explication. 
The liistory of the floras of the northern seas must be 
summarized as follows; 
In the early tertiary time there was a distinct flora in the 
Polar Sea, limited by a now disappeared landbridge from the 
atlantic flora — probably also barred from the Pacific , as the 
great difference from the present flora of that ocean indicates, 
or at least possessing very small possibilities for an interchange 
of species with that sea. Then the landbridges were broken 
and the algae of the Polar Sea got possession of ways of mi- 
gration to the south. Tlfis migration was accelerated in the 
preglacial time and the Atlantic received a considerable number 
of new citizens from the north, the Pacific a smaller one. 
When the Iceage carne the progress of glaciation drove still 
more and more species out from the Polar Sea, which became, 
if not entirely void of algae, at least very poor in species. 
After the maximal glaciation was over the algae again wandered 
into the polar regions, and this migration must still be in pro- 
gress as far as the natural conditions allow. Many of the ter- 
tiary-polar genera and species have not again been able to enter 
their old homesteads, as the present conditions there are averse 
to it. Consequently we have a number of algae, now purely 
atlantic or besides also pacific and also some solely pacific ones, 
which have their original home in the Polar Sea but are now 
lacking there. On the other hand there were old atlantic algae, 
that during the Iceage had adapted themselves to glacial con- 
ditions and after the end of the glaciation entered the Polar 
Sea together with the reimmigration of the tertiary-polar species. 
On the pacific side this kind of species seems entirely lacking, 
but notwithstanding the result must be that the present flora 
