ON THE AKTIFICIAL CULTURE OF MARINE PLANKTON ORGANISMS. 431 



Edocaiyus, GladiypJiora, Entcromorpha, Vauchcria, and unicellular algfe 

 are the commonest forms. The large seaweeds, such as Fucus and 

 Laminaria, do not live long if introduced. Plankton diatoms, although 

 a great number must be pumped up when the reservoirs are being 

 filled, are not represented. 



As in the case of outside water, a sample of " tank-water," in- 

 oculated from a persistent culture, will only give a very small growth, 

 minute forms, etc., soon multiplying and choking out the plankton form. 

 The ultimate growth of minute unicellular algse other than diatoms is 

 often considerable, and many quite unknown and unidentified forms 

 have been obtained. The total growth of vegetable forms is always 

 found to be greater than in the case of outside water. 



In cultures of plankton diatoms made with sterilized tank water, 

 a very great improvement on outside sterilized water was always 

 noted. The culture of the diatom used to inoculate this medium 

 persists for a considerable period, and the colour of the frustules 

 remains normal for two to three months. 



{(l) Aniinal- Charcoal Water. — The use of animal charcoal, as a means 

 of purifying the water in small aquaria, has for a long time been 

 known and practised by those who have kept such aquaria in 

 inland places. At an early stage in our experiments, water from 

 a tank, which was not in a satisfactory condition, was treated with 

 some powdered animal charcoal and filtered. It was noticed that 

 a good growth of diatoms took place in this water. Systematic 

 experiments with the use of animal charcoal were then conmienced, 

 and these have resulted in a method of great value, both for the 

 culture of diatoms and for the rearing of pelagic larvae. 



Animal charcoal is made by the carbonization of bones,* and is 

 «old in two grades known as "pure" and "commercial." Our earlier 

 experiments were all made with " pure " animal charcoal, but 

 subsequently the " commercial " animal charcoal was largely used and 

 appears to give equally good, if not better results. In both cases the 

 animal charcoal is used in the powdered form. Animal-charcoal water 

 is prepared as follows : — 



1. A quantity of sea-water is sterilized by heating it in a fiask to 



* Analysis of Animal Charcoal, from Thorpe's Dictionary of Applied Chcviistnj : — 

 Carbon . . . . . . . 10"51 



Ca., Mg. phosjihates, Ca. fluoride, etc. . SO "21 

 Calcium carbonate ..... 8'30 



Other mineral matter . . . . 0'98 



100-00 



