KONGL. SV. VET. AKADEMIENS HANULINGAU. BAND. 20. N:0 5. 83 



to be perfectly similar in habit to sitch as have grown farther soiithwards, where they 

 have yet been exposed to exterual conditions essentially different from those of the 

 arctic regions. Specimens of Rhodymenia palmata or Rhodomela lycojiodioides 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 

 diiferences between them. This holds good also of several other species. Hence it follows, 

 that the a]ga3 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 on the coast of Norway, 

 without any alteration being discernible in the exteriör of the plant. With other spe- 

 cies the case is different. SjJOiic/omorpha arcta and green algas 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 biolog}', or the difterences of 

 conditions have eftected even morphological difterences. For instance, Odonthalia den- 

 tata from the coasts of Spitzbergen resembles the same species from the coast of Bohus- 

 län with regard to all exteriör 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 Bohuslän in the winter-months. Polyides rotundus ofiers a pretty similar 

 instance. At Bohuslän its fructihcation takes assuredly place chiefiy in winter, on the 

 coast of Novaya Zemlya, where it occurs in a less luxuriant form, in summer. Rhodo- 

 mela lycopodioides f. tenuissi7na 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 oft' 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 steni 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 foUowing the plant from latitude to latitude. Such is the case also with 

 Chcetopteris 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 (garnets) 

 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 Bohuslän; 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 decompösition of all the organs 

 — we may call them leaves — developed during the period of vegetation more espe- 



