9 



(hpth of the fjord, was greater than that of tJie planldon of tJie North Sea and in 

 the narroiv eastern part of the Limfjord (stations 9 — 10). We cannot imagine, 

 therefore, or at any rate ouly witli great difEiculty, tliat this dense plankton 

 of the western part of the Limfjord, in its present form can have heen carried 

 into the fjord by a current from the east; but it is peculiar to the fjord on 

 nccount of its c/rcat deiisiti/. It was not positively proved by this, to be sure, 

 that tlie plankton in the Limfjord is deuser than in the Norwegian and Swe- 

 dish fjords, but only that it was of less density in the North Sea and Cattegat. 

 When one has seen, however, liow transparent the water is in tlie deep Scan- 

 dinavian fjords, just as in tiie Skager Rack and tlie North Sea, one cannot 

 after tliis doubt any more that our shallow fjords liave the densest plankton; 

 but they have such a plankton only at certain times of the year. (See later on.) 

 A closer iuvestigation of the comj)onent parts of the Limfjord-plankton shows 

 further (See the table) that other species are predominant here than in the 

 plankton of the North Sea or the eastern part of the Limfjord. 



On our first excursion tims Chætoceros debile formed the main mass of 

 the plankton of the western Limfjord, but it was not found in the North Sea 

 where, on the other haud, Bhizosolenia styliformis was dominant. Li the eastern 

 part of the Limfjord Ch. debile was quite rare, and the mass of the plankton 

 was here very insignificaut. In the Cattegat, finally, quite, another diatom re- 

 placed it, viz. Rhizosolenia alafa. The first station in the Limfjord (No. 2) was 

 very mucli like the North Sea, but it is here also that the water pours into 

 the fjord. 



Ou the second excursion, station 2 also resembles the North Sea verj' 

 much; for the rest, it is strauge to see that i\o peridinieae at all oceur in the 

 fjord at this time of the j^ear; they do not appear till we reach Nr. 11 immedi- 

 ately by the Cattegat. 



On our thii'd excursion, in July, we &.nå peridinieae throughout the whole 

 fjord, and not a few diatoms are found also in the North Sea, but the common 

 Chætoceros debile, Ch. contortum, and Skeletonema costatum do not occur tliere, 

 nor are they found in the narrow eastern part of the Limfjord. 



As the iveight of the planldon per D meter showed iis, so it is shotvn also 

 by the component parts of the planldon: the occurrence of the diatom-planliton in 

 the western part of tlie Limfjord cannot be exjdained simply by its pouring in 

 tvith the ivater from the North Sea or from the Cattegat; it must breed, in au 

 indepeudent \\'ay, in the Limfjord, so that, as a rule, it has neither the same 

 density, appearance, or composition as the plankton in the neighbouring wa- 

 ters; it occurs, in short, as a peculiar diatom-plankton. 



