v: 



''*-.' 



—I— wiiifc— Amii ihi I ifi iimii rilrrj 



21 



As all these species are really coastal forms, as Cleve him- 

 selt has found out, is it a jjriori very improbable that not one 

 Single species belongs to the shores of the Skagerak. And on 

 closer observation of the individual types this shews itself still 

 more clearly. 



Tl^e first Neritic community, the Didymus-Plankton (Nm), occurs 

 m the Skagerak during summer and autumn when the water is warm. 

 Ill hke manner we meet with the Sira-Plankton (Si) when the 

 temperature is at its lowest in the months February to April. 



There are thus two annual maxima in the Neritic Plankton. 

 J^ne one, during the warmest time of the year, formed of species 

 '^vliich are most widely diffused on more southern shores (Chwtoceros 

 didymum, Schiittii, Weissflogii, Ditylum Briyhtwelli, BiddulpUa 

 mobiliensis &c.); the other, which attains its maximum during the 

 coldest season of the year, formed of northern species, Thalassiosira 

 gravida, Norde^tsMoldii, Coscinodisous polycJiurdus, Chwtoceros debile, 

 diadema, sociale, Biddulphia crurita. On the colder, northern shores 

 (b-reenland, Spitzbergeii), where tliese species may be met with in 

 great numbers, they attain tlieir maximum daring the warmest 

 months of summer. 



If is not alone the Plankton Diatoms that have two such 

 annual periods. A like phenomenon is to be found amongst, for 

 instance, the higher Marine Algaj. 



The annuals amongst these are, either the summer forms which 



•develop during the summer, and fructify during the autumn (for 



instance Nemnlion midtifidum, Dictyota diehotoma, Cutleria nmlti- 



I ^ «, JJelesseria ruscifolia, Cystodonmm purpurascens, PolysipJwnia 



jsso'ides), or the winter forms which fructify during the spring 



( ^ytosiphon lomentarins, Dumontia fiUformis, and the Monostroma 



*^pecies). Also in respect to these it is certain that the Winter Flora 



icny consists of northcirn species; the Summer Flora, of foi-ms 



icii attain their maximum development in warmer seas. 



ine Stationary Diatoms too attain their greatest development 



of J-! 



ne same seasons, and can then cover the algse of the littoral 

 ^"th a close brown felt. 



All these forms are undoul)tedly stationary. As crusty cove- 

 S*^ to stones and rocks, they lie dormant during the unfavour- 

 alile seasons. 



itppears to us to be most natural to assume the like in 



spect to the Neritic Diatoms, when we know that they have 



e power of forming spoi-es which fall to the bottom. Through 



ESJiKs investigations 'n the Lim Fjord we have besides proof 



'■' the Neritic Diatoms may be stationarv. 

 Pi " 



LEVE sType 2 (Ns), is composed of forms, which, in liis opinion, 



^"■ne from the West Coast of Norway. He, however, says ([97] 



' ' fn'^it he is not from personal experience, acquainted with 



dnkton of the Norwegian coast, but only draws his conclusions 



the a])pearance of the species in the Skagerak. Cleve does 



give any reason on which to base this assumption, which is, 



J case, erroneous, as none of those species are typical of the 



^^'••«egian West Coast. They are all to be met with there at 



seasons, but only as subordinate constituents of the Plankton. 



Tl 



Cleve's 



ns can be seen froui 



our Tables (1, 3 & 5) and from 



Work [98]. 



later researches, mentioned in Petteksson and Ei^'Man's 



The typical forms on the AVest Coast of Norway are, as we have 

 already indicated, on the whole the same as those of the Skagerak. 

 As is usually the case with the fauna and flora of neighbouring 

 coasts, the Neritic Plankton in both places contains most of the 

 species in common, and the difference mainly consists in the rela- 

 tive numbers of the species being altered. The 4 species that 

 are named are at least as common in the Skagerak as on the 

 West Coast, and there, therefore, exists no reason for withdrawing 

 them from the others and placing them in a separate group. 



'J'his theoretically constructed Plankton group must, therefore, 

 in any case in its present form, be abandoned. If it is to be 

 replaced by any other, the West Coast Flora must be divided into 

 many communities, as the Plankton there, just as in the Skagerak, 

 changes with the seasons. 



Such a division we however consider to be of little consequence 

 so long as we do not know more of the development and life of 

 the Neritic Plankton. 



Cleve's other three types, the Arctic Neritic Plankton, Con- 

 cinnus-Plankton and Halosphsera-Plankton we will treat of shortly. 

 The first is a well defined community of high Arctic forms which 

 vegetate during winter along the whole of our Nortliern Ocean 

 shores (southern limit at Stadt), and which during summer are but 

 met with on the coasts of Greenland and Spitzbergen. 



The Concinnus-Plankton and ffalosphsera-Plankton are pre- 

 sumed to belong especially to the North Sea. We do not possess 

 sufficient materials to form an opinion on the correctness or other- 

 wise of adjudging these to be separate communities. 



The Coscinodiscus concinnus we have deemed to be Oceanic 

 on account of its close relationship to C oculus iridis. From G. 

 Mlrbay's investigations, which wo unfortunately are only acquainted 

 with from the preliminary treatise in the Fishery Boards Keport 

 [97], it appears to have spores, so that it may be regarded as 

 truly Neritic. 



Halospli(Bra too, appears to possess a sort of cyst formation*), 

 which, however, has not been more fully investigated. Its range 

 is very great, being met with from the Mediterranean, where it 

 was first discovered, to the Lofotens, and in to the very quays of 

 Christiania. 



We cannot here enter more fully into the various forms of 

 the Neritic Plankton. If these organisms are to be divided into 

 communities, one would have to arrange the species in groups, 

 according to each stretch of coast, requiring similar conditions of 

 existence, and attaining their maximum at similar seasons. In order 

 to do this we have yet too little material to go upon, but we do 

 not doubt that this can be done, and, when it is accomplished, 

 that, by comparing the development of the corresponding groups at 

 the various places, we should obtain important contributions towards 

 comprehending the climate of the ocean. 



The Neritic Diatom Plankton can, to still less an extent than 

 the Oceanic, give any basis for hypotheses concerning the flow of 

 waters from distant parts. 



The Sira-Plankton disappears, for instance, from the shores 

 of Greenland in September, appearing in the Skagerak first in 



*) Sliortly described in a preliminary note by Cleve. We also hav 

 occasionally met with such formations. 



