KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 57. NIO 7. 5 



Skag. 4. 58° 13' N., 11° O' E. 



Alsbäck (Skag. 16) 58° 19' N., ll u 33' E. (in the Gullmarefjord). 



SmörkuMen 58° 24' N., 11° 38' E. (in the Gullmarefjord). 



Kalvö fjord. 



Torsby. 



Skag. 14. 58° 50' N., 11° 7' E. 



Skag. 15. 58° 16' N., 11° 27' E. 



Before going further, I might briefly call attention to the limits of the method, 

 discussed already by Mr Gran. Firstly there is to be noted, that crustacea and other 

 plankton-animals capable of notable self-motion are very seldom caught with the water- 

 bottle, for which reason their frequency cannot be made out in this way. Secondly, 

 the numbers obtained for forms, that live only sparingly intermingled among masses of 

 dominating algae, above all diatoms, must necessarily be relatively very inexact, as more 

 exact determinations would require quantities of water, leaving after centrifugation rests, 

 too abundant for being examined under the microscope. A frequency of about 10 in- 

 dividuals per litre is the lowest limit practically discernible by the method, n. b. in a 

 comparatively poor water. Concerning all sparingly distributed forms, that may be pre- 

 sent in single specimens, from metre to metre for instance, or at much larger distances 

 still, the counting does not give any practicable result. Still, such erring and rare speci- 

 mens may be of great importance as imps for the coming regeneration of many of crop. 

 Now, in this case, valuable and completing information may sometimes be had by stu- 

 dying a material, caught at the same time with the tow-net from incomparably larger 

 water-masses; namely as far as regards big forms, being unable to pass through the mashes. 

 This partly explains the often very great discordance 1 between quantitative figures, 

 giving a somewhat adequate expression of the real frequency of a form above the already 

 quoted minimum limit, and the corresponding qualitative tables, where the same rough 

 evaluation of the frequency has been tried, as in most earlier plankton lists, and where 

 a big form, as for instance Biddulphia sinensis, or a Ceratium, may figure with a c 

 (comraon), though absent in centrifugated material. 



But in other cases, when dealing with smaller plankton-organisms, that escape 

 from the net completely or almost so, we practically know nötning for the present about 

 the biology of the rarer forms. Many small peridinia especially count among this group. 

 From their sporadic appearance in spread water-samples, no positive conclusions may be 

 drawn as yet regarding their migrations and cycle of life. These restrictions, perceptible 

 enough, when the special biology of the diff erent forms is to be treated, as will be attempt- 

 ed in part II of this work, are, however, of no practical importance for the question 

 concerned in this first part, the principal aim of which will be to give some chief data 

 relative to the amount of organic substance, produced under different circumstances 

 by our coastal waters. 



Now, the ideal thing would be to be able to calculate the total production of phyto- 



1 The incongruence is, on the other hand, often due to the presencc of masses of small nude tintinnids, 

 such as Laboea and Mesodinium, in the surface-layers. Elastic and of alterahle form, the said infusoria are 

 never caught with the net. 



