ARTIFICIAL CULTURE OF MARINE PLANKTON ORGANISMS. 367 



a single species would not be obtained. The above method is 

 similar to one described by Miquel, excepting that he placed 

 gelatinous silica at the bottom of the vessel. Some very 

 successful persistent cultures were obtained from the follow- 

 ing experiment, which will serve to illustrate the method : A 

 sample of plankton, from a very fine-mesh bolting-silk tow-net, 

 was diluted down with sterile sea-water, until a single drop 

 examined under a f in. objective contained on an averag-e 

 ten organisms, chiefly diatoms, of various species. Petri 

 dishes (4 in.), containing 60 c.c. each of Miquel sea-water, 

 were then inoculated Avith various numbers of drops of the 

 diluted plankton. The two dishes, to which two and three 

 drops respectively were added, gave the best results, and 

 from these persistent cultures of several species of diatoms 

 were obtained. Hence we may conclude that the most advan- 

 tageous number of single cells or short chains of cells to be 

 added to a 4 in. Petri dish, containing 60 c.c. culture medium, 

 is about twenty to thirty. 



We have succeeded in obtaining the following species of 

 plankton diatoms in persistent cultures : 



Aster ionella japonica Cleve. 



Biddulphia mobiliensis (Bail.) Crrun. 



Biddulphia regia (M. Schultze).^ 



Chaetoceras densum Cleve. 



Cheetoceras decipiens Cleve. 



Chsetoceras constrictum Gran. 



Cocconeis scutellum Ehr. var. minutissima Grun. , 



Coscinodiscus excentricus Ehr.^ i 



Coscinodiscus Granii Gough. 



Ditylium Brightwellii (West) Grun. 



Lauderia borealis Gran. 



Nitzschia closterium W. Sm. 



Nitzschia closterium W. Sm. forma minutissima. 



Nitzschia seriata Cleve. 



Rhizosolenia stolterfothii H. Perag. 



1 See p. 413. 

 » See p. 412, 



