372 K. J. AIJiEN AND K. W. NKLSON. 



broken-down chromatophores. AVliether regeneration can be 

 successfully obtained from a single chroinatophore, which 

 must presumably be contained within a cell-wall of some 

 kind, has not been definitely decided, but results seem to 

 point in this direction. 



At the start of a culture a tendency to teratological forms 

 is often exhibited, but when the growth is well advanced, the 

 shape of the frustules is nsually quite normal. 



(b) English ChannelWater ("Outside Water").— In 

 a large number of our experiments sea-water brought in from 

 outside the Plymouth breakAvater, and therefore taken at some 

 distance from the shore, has been used. This is referred to as 

 "outside water." It has an average salinity of about 35'0 °/qq 

 and the temperature range for the year is from 8° to 10° C. 



If a sample of "outside water" is inoculated from a persis- 

 tent culture of a plankton diatom, a small growth is obtained 

 in from five to fifteen days. But soon minute bottom forms of 

 diatoms, other algaj, flagellates, infusoria, etc., ap])ear, and the 

 inoculated species is lost. The total growth of any form is 

 never large. If the growth of these foreign forms is pre- 

 vented by sterilising the water before inoculation, a consider- 

 ably better growth of the plankton form is obtained. The 

 water was, as a rule, sterilised by simply heating to 70° C, 

 which temperature was found to be quite adequate. Boiling 

 gave equally good results, but the former was preferred, as 

 less concentration due to evaporation took place. Even 

 under these conditions no permanent culture can be obtained, 

 the diatoms soon beginning to lose colour and getting into an 

 exhausted condition. Death takes place in from two to three 

 mouths after tlie culture has been started, and in manv cases 

 considerably sooner. Long before inability to start new 

 cultures, the test of death, has been established, the valves 

 appear on examination quite colourless and practically empty. 



Samples of outside water, taken at times when the quantity 

 of plankton was widely different, gave no appreciable varia- 

 tion in the results obtained by culture methods. It is, how- 

 ever, doubtful whether differences in the amounts of growth 



