276 DISCOVERY REPORTS 



In a note on the effect of environment on form, Hendey (pp. 224-5) records his 

 general impression that conditions in warm seas favour the development of a flora of 

 relatively thin-walled diatoms of small surface : volume ratio, while diatoms in colder 

 waters have stronger frustules and a larger proportion of surface to volume. Such 

 scanty concrete observations as are available (Wimpenny, 1936; Hart, 1937, p. 444) 

 certainly favour the view that this difference in form must be ultimately correlated with 

 environmental influences. The idea raises several problems of the first importance in 

 connexion with the physiology of plankton diatoms. 



DISCUSSION OF THE METHODS EMPLOYED IN RELATION 

 TO RECENT ADVANCES IN PHYTOPLANKTON TECHNIQUE 



In recent years the main pioneer methods of studying the phytoplankton, examination 

 of routine vertical hauls with fine silk nets and of centrifuged water samples, have been 

 severely criticized by Nielsen (1933, 1938). Their probable shortcomings had long been 

 realized by their principal protagonists, and had indeed been clearly demonstrated by 

 the classic dilution experiment of E. J. Allen (1919). Nielsen apparently considers 

 them so unreliable that even observations on the broad distributional changes, involving 

 quantitative variations of many hundreds per cent, to which they have previously been 

 regarded as an adequate guide, may prove misleading. The present work has been 

 accomplished by these older methods, or modifications of them, for Nielsen's improve- 

 ments have little application in long-range work of this type, and we have some evidence 

 that conditions in the Antarctic zone are such that the errors are at a minimum. In 

 view of Nielsen's recent work, however, it is felt that the limitations of our methods 

 should be fully considered. 



The whole problem of methods in marine phytoplankton investigations is an ex- 

 ceedingly difficult one. Both Gran (1932, p. 346) and W. E. Allen (1934) point out 

 that it is very necessary that methods be adapted to the scope and aims of the particular 

 investigation. Allen says that while it is important to strive for as high a degree of 

 uniformity of method as possible, a certain degree of elasticity will nearly always prove 

 to be essential. This statement aptly defines in abstract terms the difficulties confronting 

 us in planning our programme. Antarctic surface waters occupy over twelve million 

 square miles. This is over 6% of the total surface of the earth, and some 8|% of the 

 total sea surface. For this reason alone it was essential to obtain the very largest number 

 of observations possible in order to make out even the grosser differences in the dis- 

 tribution, in time and space, of the phytoplankton. Our cruises involve absence from 

 shore laboratories for long periods, and for this reason also it seemed necessary to use 

 methods that could be completed at sea. Hence the attempt to achieve the most useful 

 working compromise between the strongly conflicting desiderata of magnitude and 

 exactitude, resolved itself into the observation of the phytoplankton by the methods 

 already described. 



The modified Harvey method has been our main standby for the study of the wider 



