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to surface, and oiie nf tlie Scaiidiuavian fjords of 1 — 200 fathoms' deptli. It is 

 only iu tlie uppennost lavers of tlie water tliat tlie latter iu summertime caa 

 reach the same degree of heat as the Liinfjord-water, and as they are always 

 rather deep quite uear the shore, the warm volumes of water will, so to speak, 

 never touch the bottom of these fjords, but only dash against the shores on a 

 very narrow tract. The bottom of the fjord, on the other haiid, is covered 

 with water, which all the year round has a temperature of c. 6 — 8 " C. It is 

 easy to understand that the couditions of the growth of animal and vegetable 

 life down liere are so different from what we see in the Limfjord, but why 

 the upper layers of water in the Scandiuavian fjords have not so rich (dense) 

 a planklon as the Limfjord, is not so readily percived, particularly because 

 the same organisms are found at both piaces, though not in the same quanti- 

 ties. We might imagine that the diatomaceæ found better conditious of food 

 iu the Limfjord-water than in the deep northern fjords, as many substances, 

 compounds of nitrogen for iustance, no doubt are carried into the Limfjord 

 from the surrounding fertile land. This thought has been expressed before by 

 V. Hensen in order to explain the different densities of Ihe plankton in gene- 

 ral. We might imagine also that the deep fjords actually produced as much 

 plankton in the surface-layers as the shallow ones, but that part of the orga- 

 nisms by little and little sink down through the cold layers below, while in 

 the shallow fjords the motion of the water compels them to keep floating 

 somewhat longer over the bottom, to that there are actually, at any given time, 

 more organisms (particularly dia omaceæ) in the mass of water. It would be 

 necessary then to point out such surface-forms in the deeper water of the deep 

 fjords, and wheu this has not been done, the reason might be that so few in- 

 vestigations with closingnets have been iindertaken, partly also, that these 

 forms will occur very scantily. because they are to be distributed in such great 

 masses of water, and perhaps quickly sink through them, perhaps are even 

 dissolved in them. It is indeed strange to see, how little we find on the bot- 

 tom, even in the Limfjord, of the masses of diatomaceæ that have lived iu its 

 water. We might expect to find its bottom covered with silicious shells, but 

 there are next to none. I must snppose that they are again dissolved in the 

 water, for they are neither carried out east nor west. It is possible, however, 

 that neither of the two said hypotheses to explaiu the different densities of 

 the plankton is correct; we must have f urther investigatious, before it is worth 

 the while to discuss the question more closely. ^^'^hen we see the water from 

 the Skager Rack, with its plankton of slight density, enter the Cattegat as a 

 bottom current, and here immediately obtain a very dense plankton, it cer- 



