287 



Remarks on the Geographical and Ecological 

 distribution. 



In the list on pp. 231 — 253 1 have given an account of the 

 general distribution of the Diatoms from Danish v^'aters. The 

 reason why, in this list and in the tables given therewith, I coni- 

 pare Europe with the other parts of the world and do not take 

 Denmark as a starting-point, is that the agreement between Den- 

 mark and Europe is so close, — of the Danish species 96 per cent 

 occur in the rest of Europe — that it seems natural, with regard 

 to Diatoms, to consider Denmark with Europe. Under the headings 

 *'Arctic" and "Antarctic" are enumerated those species which, with- 

 out regard to their distribution over other parts of the world, are 

 found far north and far south. The southern boundary for ^Arctic" 

 I have considered to be at about the Arctic circle, and the northern 

 boundary for "Antartic" at about the southern and of America. I 

 have not been able to fmd other more adequate short terms than 

 those [ have used, and I want therefore particularly to point out 

 the unusual use to which these terms have been put. 



Whenever in the list " is in parentheses it signifies that it is 

 not the species itself but a variety of it which occurs in the part 

 of the world in question, and therefore that variety is not included 

 in the percentages. Neither are the very few plankton-forms from 

 salt water included in the percentages. The new forms are absent 

 from the list, and so also, as a rule, are the variaties. Only in 

 cases where the type has not been found in Denmark, has the 

 variety been included in the list. 



I am well aware that this list of the general distribution of 

 the Diatoms may undergo alteration from time to time as new 

 works on the Diatoms appear. I have nevertheless included it be- 

 cause 1 thought it might perhaps be a help to others who, in the 

 future, may occupy themselves in investigations of a similar nature. 



If in the table II in connection with the list Australia is not 

 taken into consideration, nor the Antartic regions, which on account 

 of their as yet imperfectly known Diatom-flora yeld strongly divergent 

 percentages, theu it will be seen that the variations in the per- 

 centage-differences for the different habitats, is least (19) between 

 Europe and America, while it is greater and almost the same (25 

 — 28) between Europe and Africa, Asia and the Arctic Re- 



