KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 57. N:0 7. 



15 



The ruling Ceratium also at S. Skag. 9 is C. tripos. Prorocentrum micans re- 

 appears, and the total quantity of Peridiniales is rather high in the surface, reaching a 

 maximum of 3170 ind. per 1 and thus surpassing in frequency the corresponding vegeta- 

 tion at the Swedish-danish stations. Among these flagellates, small Gymnodinia etc. 

 are numerous. Cyttarocylis is quite single. 



Finally, the figures in tab. 13 will give an account of the total numbers of organisms 

 at the successive levels of the stations dealt with, as far as can be made ont with the me- 

 thod used. As regards the phytoplankton, the list may be considered fairly complete,» 

 but such plankton-animals as Crustaceans, Vermes, Ccelenterata etc. are rarely caught. 



Series II. November 6th-8th 1912. 



A series of samples, taken över the same section of the Skager Rak nearly three 

 months after the preceding one, shows, on the whole, a feeble increase in frequency as 

 regards the totality of the planktons, though there is hardly any form present in rich 

 quantities with the exception of Paralia. But if the råte of frequency is for the various 

 species generally a low one, the number of forms is on the contrary remarkably great. 

 The flora is a mixture of exponents for all kinds of plankton-types, among which the 

 southern oncs are prevailing, but there is for the time being no mass-development. 



This is also the season, when the temperature of the water-masses is most uniform 

 throughout, owing to vertical currents of convection, that are given rise to by the cooling 

 off of the surface- water. Also the salinity shows only small variations at most stations. 

 As might be expected, these vertical currents have, by mixing the superposed layers, 

 caused a rather uniform spreading of the plankton through the whole watercolumn. 

 Deep-water forms, as f. i. Biddulphia sinensis, reach the surface, and the homogenous 

 distribution does not get disturbed by any more rapid multiplying in the uppermost 

 layers. The season cannot be favourable to a strong growth, because of the feeble light. 



Table 14. S. Extra II. 57° 43' N., 



11° 7' 



E. 6. XI. 1912. 



c- 



0) 



p 



CB 



a, 

 g ca 



il 



o 



o 



o 



>» 



[a 



"3 



>> 



s 



c 



a 



C3 d 



"ii 



Guinardia 

 flaccida 



Thalassiosira 

 gravida 



Thalassiosira 

 Norden- 

 skiöldii 



Hyalodiscus 

 stelliger 



Rhizosolenia 

 alata, with 

 f. gracillima 



Rhizosolenia 

 fragilissima 



Thalassio- 



thrix nitz- 



sehioides 



Biddulphia 

 sinensis 



Naviculoid 



diatoms 

 + Nitzschiae 



Diatoms 



total 

 numbers 







7,69 



32,52 



25,39 



760 





60 



80 



50 



30 



150 



260 



10 



230 



1,740 



10 



7,75 



32,63 



25,48 



750 





90 



20 



10 



30 



200 



290 



20 



280 



1,885 



20 



8,59 



33,12 



25,73 



1,470 





30 





70 



30 



60 



330 



30 



580 



2,750 



30 



8,62 



— 



— 



1,290 



10 



20 



10 



10 





20 



230 





370 



2,070 



38 



8,96 



33,39 



25,88 



2,200 



20 



60 



80 



60 



1 





180 



10 



410 



3,130 



There is to note, at S. Extra II, a marked increase in the number of diatoms since 

 August. Paralia is now the dominating form here as otherwhere; it is gently augmenting 



1 The CoccoUthopltoridece here, as always, omitted. 



