436 ON THE AETIFICIAL CULTURE OF MARINE PLANKTON ORGANISMS. 



B. Experiments with a View to Determining the Conditions 



AVHICH underlie THE SUCCESSFUL CULTURE OF Dl ATOMS. 



The attempt to make cultures of diatoms for use as food, when 

 rearing pelagic larvte, led naturally to an effort to determine the best 

 culture medium and the most favourable conditions for the rapid and 

 continuous growth of diatoms. Before success can be attained in this 

 direction exact knowledge as to the nature of the essential food-stuffs — 

 and in fact as to the general physiology of the Diatomacese — is 

 necessary.* Numerous experiments, extending over the last three 

 years, have been carried out, with a view to obtaining such knowledge, 

 and the results, though still by no means complete or conclusive, are 

 perhaps worth recording. 



A great difficulty which has to be met in carrying out such investi- 

 gations on marine diatoms is caused by the fact that, when sea-water is 

 used as a basis for the culture media, we are dealing with a solution 

 of a very complex and very variable character, the exact nature 

 of which it is extremely difficult to determine. The most direct 

 method of research, namely, chemical analysis, has not proved of much 

 service, owing to the uncertainty and in many cases impossibility 

 of accurate determinations, in sea-water, of such minute quantities 

 of substances as those upon which the growth of plankton diatoms has 

 been found to depend. 



We have had, therefore, to rely, for the most part, on the lengthy 

 and tedious process of analysis by " trial and error," the experiments 

 being largely conducted on lines suggested by Liebig's well-known 

 *' law of minimums " (Pfeffer, vol. i., p. 413). The ideal at which we 

 aim is to find a culture medium, with artificially prepared sea-water as 

 its basis, such that the absence, or diminution in quantity, of any one 

 of its constituents would have a profound effect upon the growth 

 of diatoms in it. Whether the conditions regulating growth in such a 

 medium would be at all comparable to the natural conditions of life in 

 the sea is a question that would have to be decided by experiment, but 

 in any case this could be made a starting point for much more definite 

 research than has yet been attempted. Up to the present time we 

 have not, unfortunately, succeeded in finding such a culture medium. 

 Throughout the work we have had very great diificulty, in spite 

 of much care and many precautions, in obtaining consistent results. 

 It may even happen that, in two flasks containing the same culture 

 medium, inoculated with the same culture of diatom and standing side 



* For general references to literature sec Bibliography, especially Miquel (12), 



Rinhter (18). 



