268 DISCOVERY REPORTS 



no hard and fast lines can~ be drawn in nature — some gradual merging of conditions is 

 always evident — but in practice it is essential to draw boundaries somewhere in order 

 to reduce the problems to manageable proportions. It will be realized also that the 

 averages in themselves have no ' absolute ' value owing to the observational errors, and 

 the varying numbers of observations available at different times and places. They repre- 

 sent a convenient figure summarizing the existing data, and provided that due note is 

 taken of the mmiber of observations upon which they are based, should not prove 

 liable to misinterpretation. The full data from individual stations have been tabulated 

 in the Appendix. 



Results obtained in diff"erent seasons have had to be considered together, in most of 

 the areas, and this can obviously lead to serious discrepancies, but the whole region is 

 so vast that it is impossible to make any headway with our main problem without doing 

 so. I believe that our previous work, and our last big series of repeated observations 

 in one area, go far towards enabling us to detect any serious distortion due to this 

 cause. 



A few series of hydrological data, derived from the work of our hydrologists, Messrs 

 Herdman, Clowes and Deacon, with their assistant, Mr Saunders, have been considered 

 here. These were selected as fairly illustrative of the type of interrelations that have 

 been suspected from our previous work, and which should be demonstrable on a larger 

 scale when the full hydrological data are published. Incidentally, they provide strong 

 independent proof of the adequacy of our methods for following the grosser changes in 

 phytoplankton population. 



In describing hydrological features I have used the terms introduced mainly by 

 Deacon (1933, 1937) and retained the conception of the 'age' of the surface water, 

 previously found so useful in describing changes within the Antarctic zone (Hart, 1934, 

 p. 10), and which has subsequently proved helpful in the consideration of observations 

 in northern waters also (Nielsen, 1937, p. 151). 



Differences in phytoplankton population have been expressed so far as possible in 

 the terms advocated by Gran and Braarud (1935, p. 332). I have eschewed the use of 

 the words 'association' and 'succession' as applied in my earlier work on account of 

 their specialized connotation in terrestrial plant ecology.. One must agree with these 

 authors on this point, but I venture to suggest that with the rapid increase of speciali- 

 zation in all branches of ecology, there is grave danger that any language will soon be 

 bereft of suitable descriptive terms that one can use in a general sense, without tres- 

 passing upon the jargon of this or that branch. The difficulty of describing new pheno- 

 mena, or known phenomena taking place on a hitherto unrecognized scale, is thereby 

 enormously increased. 



The phrases ' main phytoplankton increase ' or ' main increase ', to describe the period 

 of maximum production, have been used in preference to the ' spring diatom growth ', 

 'diatom flowering' or 'spring increase' of workers in the northern hemisphere. This 

 has been found more convenient because in the southern hemisphere, with its very 

 much lower temperatures in corresponding latitudes, the increase takes place later in 



