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



41 



already propagating in a more lively measure in the uppermost, Baltic layers, the maxi- 

 mum for the Protozoa being about 6,000 per 1 in the surface of S. Skag. 0. Also at S. Skag. 

 9, they are not rare, but at the outer stations 5 — 8 there is very little of tliem. They will 

 thus be found to follow the Sira-plankton. At the southeastern stations were registered 

 up to 7,600 ind. per 1 of the dubious small Bion mullispmosum, which seems to me to 

 present a great resemblance to vegetal spores or pollen. 



Series VI. April 17th 18th 1914. 



Taken about seven weeks af ter the February series just dealt with, this last collec- 

 tion will above all serve to give an idea of the development of that diatomaceous spring 

 vegetation, which succeeds to the winter-flora still ruling unrivalled in February. Here 

 as well as in April 1913, the leading form, that we will ha ve to follow more attentively, 

 is Leptocylindrus danicus. This species was eertainly present in small quantities already 

 in February, but it was then hardly showing any signs as yet of beginning multiplication 

 even at the southernmost stations. 



Table 63. S. Extra II. 57° 43' N., 11 C T E. 17. IV. 1914. 



■13 



Q 



c - 



Salinity °/<"> 

 Density s t 



Thalassiosira 

 grovida 



■z 

 t. 



o ä 12 



._ C5 -C 

 "' t. :C 



— ° 12 



Lauderin 

 borealis 



Coscinodis- 

 cus con- 



Sceletonema 

 costatum 



Paralia 

 suloata 



Cerataulina 

 Bergonii 



Guinardia 

 flaccida 



Biddulphia 

 sinensis 



Eucampia 

 zodiacus 



Asterionella 

 japonica 



Leptocylin- 

 drus danicus 



Rhizosolenia 

 semispina 



to 



s l 



<D 3 

 o ■*> 



° fe 



-u o 



C3 C 



J3 O 



O ° 



Diatoms 



total 

 numbers 















31) 



560 



320 



520 











1,260 



980 



280 



5,390 



7,54 



22.63 



17,68 



10 



5,03 



31,15 



24,64 



40 



60 



85 



3,600 





130 



340 



20 



300 





66,800 



6,250 



10,400 

 + 1,100 



118,580 



20 



5,45 



32,66 



25,80 



55it 

 1,000 



100 

 50 



85(1 



800 25! I 

 + 100 ] 



1,030 

 3,450 



400 



150 

 450 



500 

 550 





350 

 1,250 300 



16,150 

 2,300 



3,350 

 2,750 



10,550 



2,750 



53,210 

 28,875 



30 



5,38 



32,75 



25,88 



38 



5,36 



33,69 



20,61 



1,650 



450 



2,350 50 



27,650 



1,600 



400 



1,000 



10(1 



100 



950 



2,750 



2,050 



5,550 



68,450 



The more uniformly dilute February-water has now given plaee to a somewhat 

 salter and 2° warmer medium up to less than 10 m, where there is a sharp limit, the thin 

 surface-layer being strongly diluted. Southern forms, such as Guinardia and Cerataulina, 

 are almost unchanged since February and reach up to the 10 m-level, Cerataulina and 

 Paralia even to the surface; the latter is gradually leaving the waters. Biddulphia si- 

 nensis at 10 m and relatively much of Eucampia zodiacus demonstrate a continued in- 

 flow of southern bank-water. The remnants of the winterly Sira-plankton are distinctlv 

 sedimenting towards the bottom, while the Leptocyl indrus-f ormation of spring-diatoms 

 is developing chiefly in the 10 — 20 m layer, just getting cleared from the former. Yet, 

 Leptocylindrus seems to be far from its maximum, as its frequency does not exceed 66,800 

 ind. per 1, a very low number, compared to that found in April the year before. It is 

 most doubtful, if Leptocylindrus this year will ever come to attain the frequency of the 

 year before, the relatively high proportion of Southern North-Sea-water, now present 

 at S. Extra II up to so high a level as 10 m, being eertainly hinderly to its propagation. 



K. Sv. Vet. Akad. Handl. Band 57. N:o 7. 6 



