426 ON THE AKTIFICIAL CULTURE OF MARINE PLANKTON ORGANISMS.' 



Chcctoccrris densiim, Cleve. 



Chcctoccras dccipiens, Cleve. 



Chcetoceras constridum, Gran. 



Cocconcis scutellum, Ehr. var. minutissima, Grun. 



Coscinodiscus exccntricus, Ehr.^ 



Coscinodiscus Granii, Goush. 



Dityliiim BrightweUii (West), Grun. 



Landcria horcalis, Gran. 



Nitzschia clostcrinm, W. Sm. 



Nitzschia dosterimn^. ^m.., forma minutissima. 



Nitzsdiia seriata, Cleve. 



Rhizosolcnia stolterfothii, H. Perag. 



Skdetonema costatum (Grev.) 



Streptotheca thamensis, Shrubs. 



T/ialassiosira deciijiens, Grun.* 



It is hardly necessary to add that in dealing with tliese cultures^ 

 similar precautions to those used in bacteriological work must be 

 taken, all vessels and instruments being carefully sterilized before they 

 are brought into contact with the prepared sea-water. The cultures 

 are best made in small, wide-mouthed flasks, which may be plugged 

 with cotton wool, or simply covered with watch-glasses. The flasks. 

 should be kept at as uniform a temperature as possible (from 12°-17° 

 C.) and should be exposed to strong daylight, direct sunlight being 

 avoided. A flask should not be more than half filled with culture 

 fluid, so that the surface exposed to the air may be large in pro- 

 portion to the volume of fluid. 



Other Methods. The addition of the solutions devised by Miquel ta 

 sea-water has in all cases given us good cultures of diatoms, and the 

 method is certain in its action. We have, however, made numerous 

 experiments by treating sea-water in other ways, with a view to 

 finding out what are the best conditions under which plankton 

 diatoms will grow, and of arriving at some explanation of the action 

 of the different salts contained in Miquel's solutions. 



2. Hoiighton Gill's Method. H. Houghton Gill (5), a contemporary 

 of Miquel, made use of a culture medium not essentially difl'erent 

 from that employed by the latter. Unfortunately he died before pub- 

 lishing his work, but an account of his principal results is given by 

 Van Heurck. In his final method Houghton Gill made use of four 

 distinct solutions, as follows : — 



* See p. 460. 



