17 



species are coloured blue, the Neritic red (Southern), brown (Nor- 

 thern) and green (Arctic). 



The tones of the colours denote the approximate quantity of 

 the corresponding species, the name of which will be found at the left, 

 just beyond the horizontal lines. The tones correspond with the 4 

 markings given by CLEVE, r (lightest), -f- (2 tones), c (3 tones), 

 cc darkest tints. Of the green colouring there will be found but 

 the two lightest shades, and of the brown but the three lightest. 



It must be stated that CLEVE'S markings, which we have, 

 hitherto, adopted in all our investigations, but form a very small 

 scale for the comparison of the quantitative distribution of the species 

 in the samples. The indication cc, corresponds to a frequency which 

 is at least 1000 times greater than denoted by r. Neither the 

 Tables, nor the graphic deliniation on PI. 4, give, therefore, an 

 adequate idea of the diversity, which, in reality, is very great. 



On PI. 4, it will be seen that the temperature in 1896, in- 

 creases from the coast outwards towards the bodies of water in 

 the Gulf Stream, after which it gradually decreases as it approaches 

 the Polar current. The same was the case in 1897, with the 

 exception that the temperature was, throughout, about 2 lower, 

 owing to the greater development of the Polar current. 



In 1896, the Oceanic Diatoms were so distributed that Clice- 

 toceros decipiens attained its maximum at St. V (surface tempera- 

 ture 9.6), Thalassiothrix longissima between St's. VII and VIII 

 (Temperature respectively 6 and 5.2), and Coscinodiscus oculus 

 iridis at St. VIII (Temperature 5.2). The Rhizosolenia styliformis 

 was not met with at any of the stations in great numbers. It 

 attains its greatest development somewhat later in the summer 

 when the water has become more heated. 



In May 1897, none of the species had become developed to 

 any appreciable extent. 



We thus see that each individual species attains its maximum 

 at different places, and under different conditions of life. Probably 

 it is the temperature which has the greatest influence on their 

 development. 



As the various Oceanic currents do not afford the organisms 

 like conditions of existence, the Plankton may, in many instances, 

 be employed as a means of distinguishing waters of different origin. 



The Diatoms may easily be observed, especially on account of 

 their occurrence in masses, and their various appearances at various 

 spots may, in many instances, stamp the Oceanic currents. 



This is illustrated, too, on PL 4, Fig. 1. The Stations II 

 IV*) are near the Norwegian coast, and the coastal currents with 

 their low salinity go from the surface down to a depth of 60 to 

 100 metres. 



The Plankton contains scarcely any diatoms, only some indi- 

 viduals of Oceanic species, but, on the other hand, great quantities 

 of peridins , (especially Ceratium tripos and the variety longipes, 

 which however is not separated from the main species). 



Stations V VII**) are situated in the waters of the Gulf 

 Stream, as will be seen from the dark blue colours on the profile 

 (salinity exceeding 35 % ). 



*) On the Tables, Stations 4245. 

 **) On the Tables, Stations 46, 50, 54. 



The samples of Plankton contained masses of Diatoms, and 

 no appreciable difference existed between the surface Plankton (1st 

 column) and that of the deep (2nd column). Amongst the Oceanic 

 species, not a few Neritic species were met with, which in such 

 salt water found favourable conditions of growth. They would pro- 

 bably, however, have proceeded further with the current for a short 

 time, as most of them possessed numerous spores. (Chcetoceros 

 cinctum, constrictum, diadema). 



At Stations VIII IX, the Atlantic water was covered by 

 fresher Arctic Ocean water (light blue colouring), which, however, 

 then formed but a layer of about 80 metres in thickness. The 

 Plankton there was poorer both in quantity and quality. The 

 Neritic Diatoms were entirely wanting, and the Oceanic were some- 

 what scarce on the surface, whilst met with still in great numbers 

 in the samples taken from a depth of 100 metres to the surface. 

 In procuring these samples the net was thus drawn through partly 

 Atlantic water. 



Stations X XI, furnished an excessively poor Plankton yielding 

 but quite few individuals of the most hardy forms. In the Arctic 

 Ocean water therefore, the Diatoms had not at that period of the 

 year commenced their development. 



In May 1897 (PI. 4, Fig. 2) the Arctic Ocean water was still 

 very deficient in organisms, and even in the Gulf Stream, the 

 development was delayed on account of the cooling influence of 

 the Polar current. 



From these examples it will be seen that a study of the 

 Plankton, together with purely hydrographical investigations, may 

 be of great value in discerning layers of water of different sources 

 of origin, in the present instance too, the water in the Norwegian 

 coastal currents, the Gulf Stream and the Polar current. 



In other instances, however, the Plankton gives but little in- 

 formation concerning the Ocean currents. Thus, for instance, both 

 the Gulf Stream and Polar current are very deficient in Diatoms. 

 This will be seen, for instance, if Table 7 be compared with the 

 corresponding Table B III (Fig. 11), or with the profile PI. 5, 

 Fig. 1. The species which occur are the same in both currents, 

 while no considerable quantitative difference can be observed. 



If the investigations in respect to the Plankton are to be em- 

 ployed to any great extent as hydrographical aids, the life and 

 distribution of the Plankton organisms must be first thoroughly 

 known, as, otherwise, hasty conclusions might be drawn from them. 



Firstly, the Oceanic Plankton changes its character with 

 the seasons, just as does the life of plants and animals on the 

 coasts, so that the same current at different periods of the year 

 can convey with it different organisms, for instance into the 

 North Sea. 



Secondly, the very same current becomes gradually chilled or 

 heated during its course; possibly also undergoes slight changes in 

 its salinity and gaseous contents. On PI. 4, Fig. 1, it will thus be 

 seen that the temperature and salinity of the Gulf Stream decrease 

 as its waters approach the Polar current. 



Such changes will, no matter how gradually they occur, affect 

 the nature of the Plankton, as they retard the development of some 

 species, and promote that of others which possibly may have, pre- 

 viously, appeared in such small numbers, as to have escaped 



