34 



C A H LINE I j F, E G A A R II. 



STATION F 41. 



This station was interesting on account of the very rieh occurrence of Achnanthes 

 taeniata, which showed the maximum of 3905000 cells pr. litre in the depth of 5 mètres. 



This station was distinguished ftom the other stations by the différence, which 

 existed hetween the upper and the deeper layers of the water. This fact is not shown 

 very distinctly by the température, which decreases from 3,60" (0 mètres) to 1.31° 

 (20 mètres) and then increases to 3,26° (50 mètres). But the salinity makes it very 

 apparent heing rather low (3,68 %o — 3,84 %o) from to 10 mètres and considerably 

 higher (5,32 %o — 6,35 Voo) fr° m 20 to 50 mètres. No observations of oxygen-tension 

 were made. 



The plankton-mass is found in the upper layers to the depth of 20 mètres. We 

 find, that the plankton-limit lies somewhat deeper than the hydrographical limit. This 

 fact can be explained by the sinking of the plankton-organisms. 



The water of the upper layers with low salinity lias corne from the river Neva, 

 which lias very nutritive water. It is probable that the flourishing state of the diatoms 

 is owing to this rieh supply of food from land. 



The plankton was very poor in the water-layers deeper than 20 mètres. Achnan- 

 thes taeniata was found in rather large numbers, but still reduced in eomparison with 

 those of the upper layers. 



The following species were dominating: 



Achnanthes taeniata with and without resting-spores. 



Chaetoceras Wighami 



Diatoma tenue 



Fragilaria cylindrus 



Melosira hyperborea with and without resting-spores. 



Gonyaulax catenata. 



Chaetoceras Wighami has not yet formed resting-spores. This diatom is probably 

 increasing, while Achnanthes taeniata and Melosira hyperborea, which have formed 

 resting-spores, are decreasing. 



In order to illustrate the conditions of this station better. we will tabulate the num- 

 bers of the total sum of diatoms pr. litre and the numbers of Gonyaulax catenata pr. 

 litre (table III): 



Table III. St. F 41. Number of cells pr. litre. 



Tom. XLVni. 



