KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND. 20. N:0 5. org) 
to be perfectly similar in habit to such as have grown farther southwards, where they 
have yet been exposed to external conditions essentially different from those of the 
arctic regions. Specimens of Rhodymenia palmata or Rhodomela lycopodioides f. typica 
that have lived in deep water on the coasts of Spitzbergen or Novaya Zemlya, are 
found to agree so completely as to external and internal anatomical characters with 
specimens of the same species growing within the litoral zone on the west coast of 
Norway, that even the most sharpened eye cannot detect other than merely individual 
differences between them. This holds good also of several other species. Hence it follows, 
that the alge in general, and particularly the arctic forms, have a great ability to 
adapt themselves to different external conditions without being influenced by them in 
any sensible degree. The pressure to which a Rhodymenia palmata is exposed in the 
Greenland Sea, the temperature at which it lives here, and the quantity of light that 
is afforded to it, are all most essentially different from those ou the coast of Norway, 
without any alteration being discernible in the exterior of the plant. With other spe- 
cies the case is different. Spongomorpha arctu and green alge in general, as well as 
several others, certainly agree in morphological characters with their southern co-species, 
but they never attain the same luxuriancy, strength, and richness as farther to the 
south. Again, other species agree with their co-species in the south as to the form 
and development of the organs, but differ from them in biology, or the differences of 
conditions have effected even morphological differences. For instance, Odonthalia den- 
tata from the coasts of Spitzbergen resembles the same species from the coast of Bohus- 
lan with regard to all exterior parts, but while developing in the former locality its 
tetrasporangia at the middle of summer, viz. at the end of July, it is found with such 
organs at Bohuslin in the winter-months. Polyides rotundus offers a pretty similar 
instance. At Bohuslan its fructification takes assuredly place chiefly in winter, on the 
coast of Novaya Zemlya, where it occurs in a less luxuriant form, in summer. Rhodo- 
mela lycopodioides f. tenuissima on the north coast of Spitzbergen needs continue its 
development throughout the whole year, in the Ochotsh Sea as well as on the north- 
eastern coast of Siberia part of the year suffices for it. After having here at the end 
of the season thrown off part of the side-organs formed, it rests for some time. Then 
it begins again to develop new parts from the surviving rests of the stem and the 
branches. This difference in the mode of life causes such a considerable difference in 
the external form, that one would not hesitate to regard the Spitzbergen form as spe- 
cifically different from the Siberian, if the falseness of such a view were not demon- 
strated by following the plant from latitude to latitude. Such is the case also with 
Chetopteris plumosa, so common in the arctic region. On the coasts of Spitzbergen as 
well as on the west coast of Sweden, the period when it forms its zoospores (gamets) 
is in winter. At this time the aspect of the plant in the two localities is very diffe- 
rent. At Spitzbergen it has preserved all its assimilating external organs, that is to 
say, it resembles the summer form at Bohuslan; at the latter place, on the contrary, 
the formation of those side-parts by which the zoosporangia (gametangia) are supported 
and particularly developed, is preceded by a far gone decomposition of all the organs 
— we may call them leaves — developed during the period of vegetation more espe- 
