ARTIFICIAL CULTURE OF MARINE PLANKTON ORGANISMS. 363 



knowing what organisms were introdnced into the acjuaria in 

 which the larva? were to be reared, either in the original sea- 

 water or along with the food supply. 



It appeared, therefore, at an early stage of the work, worth 

 while to make an attempt to carry out rearing experiments 

 on a more definite and precise plan, to endeavour, in fact, to 

 introduce the larvae to be reared into sterile sea-water, and 

 to feed them with pure cultures of a suitable food. This was 

 the ideal to be aimed at. As a matter of fact it has seldom, 

 if ever, been attained in practice ; nevertheless, a consider- 

 able measure of success has been achieved by working upon 

 these lines, and during the course of the Avork innumerable 

 problems relating to the physical conditions under which 

 plankton organisms can best flourish have presented them- 

 selves. Some account of the experiments made may be of 

 interest to other workers, although nmny of the problems 

 raised are not yet solved, notwithstanding tlie fact that some 

 1500 cultural experiments have been under observation. It 

 is rather with a view of stimulating other work upon similar 

 lines than of bringing forward conclusive results, that this 

 paper is being published. 



In the summer of 1907 Mr. E. W. Nelson became associated 

 with the investigation, and since that date the experimental 

 work has been carried out by him. The discussions in this 

 paper of a more chemical character, particularly the section 

 on alkalinity, are almost entirely the work of Mr. Nelson, and 

 we have both had throughout the advantage of the constant 

 advice and help of Mr. D. J. Matthews on all such matters. 



I. Culture op Plankton DiatomsI 



(a) Practical Culture Methods. 



1. MiquePs Method. — Attention was first directed to 

 the culture of plankton diatoms ; and the methods, which 

 had been elaborated by Miquel (11) for fresh-water diatoms 

 a.nd had been found by him to succeed with marine bottom 

 diatoms, were tried. 



